Environmental and Experimental Botany

Stomata are the pores on plant surface, and these tiny pores are responsible for the flow of gas between plants and atmosphere. Currently, what effects of the broad and continuous increase in stomatal density achieved via genetic engineering on plant growth and development remain poorly understood. The 9 Arabidopsis transgenic lines with increased stomatal density were acquired through overexpressing FSTOMAGEN (the homologs of STOMAGEN, which are in Flaveria). The intermediate stomatal density (SD) lines exhibited increased trend in biomass. Compared with the lines with low SD, the biomass of Arabidopsis lines with intermediate SD (484 mm-2) significantly increased. There was a positive and significant correlation between biomass and relative water content. Across these transgenic lines, only during the earlier phase of growth, the leaf area exhibited a gradually increased trend as stomatal density increased, and there was both a significant linear relationship between SD and leaf growth rate and a strong linear relationship between SD and leaf area. In contrast, a clear relationship during the later phase wasnt observed. Under lower growth light intensity, there was an increased trend of biomass from other lines to the lines with intermediate SD, and the photosynthetic rate and stomatal conductance of the intermediate line were significantly increased. This study reveals plant-growth alterations that correspond to broad and near-continuous increases in stomatal density achieved via genetic engineering. Our study sheds light on the prerequisites for elevated stomatal density achieved via genetic engineering to promote plant growth.

Concurrent exposure to heat and drought stress compromises legume productivity, yet their combined effects are rarely quantified systematically. We compiled a database of 18 studies covering seven legume species. From these, we extracted 929 physiological, biochemical, and yield-related traits and calculated actual-to-additive ratios to classify heat-drought interactions as antagonistic (ratio < 1), additive (ratio = 1), or synergistic (ratio > 1). Additive heat-drought relationships accounted for 59 % of all classifiable observations, 37% relationships were antagonistic, and 4% synergistic. The relationship varied with species, genotype, trait, and experimental conditions highlighting the complexity of combined abiotic stress effects. The results challenge the common assumption that concurrent stresses invariably exacerbate damage and underscore the need for more realistic, quantitatively defined stress treatments as well as frameworks that integrate trait-level responses into predictive models of crop growth and development. Our synthesis provides a quantitative foundation to understand legume phenotypes under the increasingly frequent co-occurrence of heat and drought stress and identifies research areas where further work is needed to improve insight into combined stress responses. HighlightsO_LICombined heat and drought responses were mainly additive or antagonistic. C_LIO_LIEvidence is biased toward few legumes and controlled environments. C_LIO_LIField-based, multi-species studies are needed to identify adaptive traits. C_LI

Plant root cellular architecture and cell wall composition influence plant productivity, stress resilience, biotic interactions, and potentially soil carbon accumulation. This study establishes comprehensive compositional parameters for roots of a lowland switchgrass genotype, DVR3. Root traits were analyzed in 12.5 cm depth segments, from Zone 1 near the surface to Zone 4 down to 50 cm. Mean abundance ({micro}g/mg) for major cell wall components included cellulose 470 {+/-} 20, xylose 250 {+/-} 20, lignin 170 {+/-} 15, and total suberin 35 {+/-} 5. Composition and cellular anatomy varied with depth, in a partially coordinated manner. Cross sections showed extensive aerenchyma in mature root regions despite greater root mass density, corresponding to abundant lignin and cellulose. Deep roots were enriched for pectin-associated traits, including arabinogalactan II, homogalacturonan, and arabinose-associated linkages. Suberin content did not vary significantly, though Casparian strip formation, endoderm and exoderm thickening, and suberin surface staining progressed with development. Similar trends in root lignin and specific root length were observed for another lowland switchgrass genotype, AP13. These results suggest that it may be possible to genetically enhance native switchgrass root chemistry to promote soil penetration and below-ground carbon accumulation by reducing variability with development, potentially via cell-type specific adjustments. HighlightOlder, shallower switchgrass crown roots are enriched in lignin and cellulose, and deeper, younger roots are pectin-rich with juvenile cellular anatomy. A more uniform compositional distribution might enhance below-ground traits. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=120 SRC="FIGDIR/small/744798v1_ufig1.gif" ALT="Figure 1"> View larger version (47K): org.highwire.dtl.DTLVardef@159de98org.highwire.dtl.DTLVardef@124d714org.highwire.dtl.DTLVardef@1a49c14org.highwire.dtl.DTLVardef@2fa67_HPS_FORMAT_FIGEXP M_FIG C_FIG Schematic summary of switchgrass root anatomy and composition across four 12.5-cm depth zones of a 50-cm root system. Zone 1 represents older, shallow roots and Zone 4 includes younger roots and root tips. Representative cross-sections show greater aerenchyma development in older roots than in young root tips. The compositional heatmap shows higher cellulose, lignin, and xylose in Zone 1, higher pectin and nitrogen in Zone 4, and relatively little variation in suberin across zones.

Utricularia gibba L. is an aquatic carnivorous plant with a diverse set of capabilities. Reddening of traps frequently occurs in old in vitro cultures. While anthocyanins are often responsible for red coloration in plants, not every plant turns red. Stress factors like high light or excess sucrose have previously been shown to induce the formation of anthocyanins. Here, we hypothesized the red trap formation to be dependent on nutrient deprivation and tested nitrogen deprivation. The results suggest, that only in combination with light, nitrogen deficiency leads to the activation of the complete anthocyanin biosynthesis pathway and visible red coloration. However, in darkness, anthocyanin biosynthesis appears generally less active compared to light conditions and expression of most anthocyanin biosynthesis genes is not significantly upregulated under nitrogen deficiency.

Salinity stress affects rice productivity due to reduced growth and sodium ion toxicity. Previously, we identified a splice variant of RADIATION SENSITIVE23a (RAD23a) as the potential basis for variation in salt-tolerance in rice germplasm. RAD23 is a known moonlighting protein associated with protein degradation. To validate the role of RAD23a in salt stress response, we characterized gene edited mutant lines that targeted the UBL and UBA2 domains of this protein. Mutation in either domain promoted shoot growth under saline and control conditions. The mutants also differed from wildtype plants in Na and K accumulation in roots and shoots under salt stress. Transcriptome analysis of mutants versus wildtype showed differential transcript abundance of multiple inorganic phosphate (Pi) starvation related genes, including OsSPX2 and OsPHO2. As a result, mutants accumulate higher Pi compared to wildtype plants. The two allelic groups for RAD23a locus also differ in root and shoot phosphorus (P) content. Further, we show that RAD23a interacts with OsSPX2, a negative post-translational regulator of OsPHR2, the master regulator of Pi starvation response. Mutants have higher shoot growth and Pi levels under low Pi conditions, linking enhanced growth of mutants to increased Pi uptake. The UBA2 domain specific mutants have higher single grain weight and per plant grain weight than wildtype. In summary, we show that the RAD23a regulates differential growth, salt response and Pi uptake in rice in a domain-specific manner supporting the moonlighting roles of RAD23a in salt tolerance and phosphorus-dependent shoot growth.

Bluebunch wheatgrass (Pseudoroegneria spicata) exhibits substantial variation in its response to salt stress, making it a valuable model for studying salinity-tolerance mechanisms for use in crop improvement. In this study, we identified two P. spicata genotypes with contrasting responses to salt stress: the tolerant W6 56551, which maintained growth with green foliage under saline conditions, and the susceptible PI693916, which exhibited severe leaf chlorosis and stunted growth. To better understand the molecular basis of salt tolerance in blue-bunch wheatgrass, we conducted RNA-sequencing at 0, 1, and 4 days (D0, D1, and D4) after salt treatment at 160 mM level to examine changes in gene expression of salt-tolerant and salt-susceptible genotypes. Comparative analysis across time points identified 6,154 and 1,086 differentially expressed genes (DEGs) at D4 and D1 in PI693916, and 4,638 and 3,302 DEGs at D4 and D1 in W6 56551, respectively, relative to control (D0). Functional analysis of these DEGs showed that the salt-tolerant geno-type displayed an early and broad transcriptional reprogramming, including induction of photosynthesis, carbon metabolism, and flavonoid biosynthesis pathways, whereas the salt-susceptible genotype exhibited delayed and less coordinated responses, with enrichment of cyanoamino acid metabolism and repression of antioxidant-associated pathways. Notably, calcium signaling, ion transporter regulation, and osmolyte biosynthesis genes showed contrasting expression between genotypes, highlighting distinct strategies for ionic and osmotic homeostasis. Collectively, these results demonstrate that salt tolerance in P. spicata is associated with rapid metabolic adjustment, enhanced photosynthetic stability, and differential regulation of ion transport and osmoprotectant pathways.

Accelerating photoprotective regulation to improve carbon assimilation is a promising strategy to increase crop productivity. Although rapid non-photochemical quenching (NPQ) relaxation has been validated as a target through metabolic engineering, it remains unclear whether conventional breeding has improved this trait. Here, we investigated whether more than a century of soybean breeding enhanced NPQ relaxation alongside light-saturated carbon assimilation and seed traits. We evaluated a historical panel of 24 soybean genotypes across vegetative and reproductive developmental stages by integrating NPQ relaxation, gas exchange parameters, xanthophyll-cycle pigment profiles, expression of key photoprotective genes (VDE, PsbS, and ZEP), seed number and seed weight. NPQ relaxation parameters were not consistently associated with genotype release year, seed number, or seed weight at either developmental stage. The only exception was the amplitude of the rapidly relaxing NPQ component (AqE), which was negatively correlated with all three variables during the reproductive stage. In contrast, genotype release year was positively associated with maximum net CO2 assimilation rate (Amax), maximum carboxylation rate of Rubisco (Vcmax), maximum electron transport rate (Jmax), seed number, and seed weight, while Amax and Vcmax were positively correlated with seed number and seed weight. These findings indicate that the greater photosynthetic capacity of modern genotypes was not accompanied by faster photoprotective response. Thus, photoprotective regulation has not kept pace with gains in photosynthetic capacity under field conditions. We conclude that rapid NPQ relaxation remains an important target for synchronizing photoprotection with the high photosynthetic capacity of modern soybean lines.

Optimum irrigation and fertilizer nitrogen (N) rates are important to improve crop yield at reduced environmental risks in the form of NO3-N leaching losses, without any financial loss. The study aimed to investigate the impact of rational irrigation and nitrogen management on wheat and maize crop yield vs. NO3-N leaching losses, with field experiments conducted at the experimental station, University of Agriculture Faisalabad, Pakistan, for two years, with wheat-fallow-corn seasons each year. Suction lysimeter were installed for collection of leachates while soil water balance was computed using the HYDRUS-1D model. We explored the various management strategies, including three irrigation and N levels (sub-optimal, optimal, and supra-optimal, referred to as I1, I2, and I3 for irrigation, and N1, N2, and N3 for nitrogen, respectively) for wheat and maize crops. The three irrigation levels were 325, 400, and 475 mm for wheat, and 375, 525, and 675 mm for maize crops. The three N-levels were 100, 130, and 160 kg ha-1 for wheat, and 220, 270, and 320 kg ha-1 for maize. The results indicated that increasing the irrigation and nitrogen levels significantly improved the growth and yield of both crops during both seasons. The highest grain yield of wheat (4.0 t ha-1) and maize (7.8 t ha-1) was observed with I3N3; however, I2N3 showed statistically no difference in yield, while showing significantly reduced (28.6%) annual NO3-N leaching losses of 23.8 kg ha-1, and the highest financial benefits of 780$. Sub-optimal levels of irrigation and N, though reduced the NO3-N leaching losses, caused significant yield losses, generally unacceptable to the farmers. Irrigation water use efficiency (WUEi) also improved by 12% in wheat and 20% in maize under I2 than that of the I3 level. Besides, considering economic profit, the highest value cost ratio (1.64 and 2.04 in wheat and maize, respectively) was achieved under the I2N3 treatment, as opposed to the other treatments. Based on comprehensive analysis, the I2N3 treatment is recommended for sustainable yield and minimal environmental risk in the wheat-maize cropping system. Moreover, it was observed that the rainy fallow period contributes 14.0-31.5% of the total NO3-N leaching losses. Further investigation is needed to minimize NO3-N leaching losses, especially during the rainy fallow period, by early maize sowing and increasing the efficiency of N fertilizer (such as fertilizer coating) under the flood irrigation system, to achieve the potential goals of sustainable productivity and environmental security.

Drought stress is the major yield limiting factor in upland rice production where the moisture availability is highly variable. Understanding and evaluating how upland rice responds to drought stress is critical to improving resilience and yield stability. In this study performance of sixteen upland rice varieties were evaluated under non-stressed, moderately stressed and highly stressed conditions. Drought stress was introduced by irrigating upland rice at 70% and 50% field capacity (FC) whereas non-stress treatment was irrigated at 100% FC. Irrigation in moderately stressed and highly stressed conditions was also withheld for six days at lateral crop stages to observe temporary wilting by inducing a stress interval. Data on agronomic traits of upland rice was collected in three experimental replications. Results indicated that performance of upland rice varieties was significantly altered under stress conditions and highest performance was observed under non-stressed conditions. Yield losses for short duration and long duration varieties ranged 35-60% and 24-62% under moderate stress whereas it ranged 43-78% and 52-73% under highly stressed conditions, respectively. Overall varieties Dawk Kha, Khao/ Sai and Dawk Pa-yawm, indicated higher stability under stressed conditions therefore, these long duration varieties could be used for obtaining better yields under diverse agroclimatic conditions and under unpredicted weather patterns. Short duration Ma-led-nai-fai and long duration Goo Meung Lung and Bow Leb Nahag could be used for acquiring traits for higher tillering and panicle bearing capacity. Short heighted varieties such as Jao Daeng, Sahm Deuan and Ma-led-nai-fai could be used in breeding for short heighted new varieties to overcome lodging concerns. Strong significant association of GMP, STI, MPRO, MHAR with grain yield under non-stressed, moderately stressed and highly stressed conditions indicated that these indices were appropriate for their use as selection criteria for drought resilience.

Context. Barley production requires advanced knowledge of its response to changing environmental conditions in order to keep it competitive and sustainable. Aim. Advance in the understanding of barley phenology and foliar development under South American field conditions. Methods. 8 spring barley genotypes with differential phenology were studied in four field experiments under different temperature (through years and sowing dates) and photoperiod (through sowing dates) conditions. Time to anthesis, emergence to onset of stem elongation, stem elongation to anthesis, photoperiod response (PR) in these three traits, number of final leaves at anthesis (FLN) and phyllochron were measured. Key Results. Time to anthesis and its subphases were shorter in late plantings but under similar photoperiod, temperature increased them. Cultivars have differential responses but with magnitude interactions and not crossover ones. Cultivar effects defined PR with no interaction with year (temperature). Temperature and photoperiod affected FLN, phyllochron and their relationship with time to anthesis. Under the shorter photoperiod, FLN and phyllochron were negatively correlated, FLN was higher in the warmer year and positively correlated with time to anthesis while phyllochron was not affected by temperature and had no correlation with time to anthesis. Under longer photoperiod, phyllochron was higher in the warmer year and time to anthesis was positively correlated with both FLN and phyllochron. Conclusions. Cultivar basal thermal requirements and PR were consistent under the different studied conditions. Changes in temperature and photoperiod affected the relationship between time to anthesis, FLN and phyllochron suggesting that, although the three traits are arithmetically related, environmental conditions affect their balance.

Salinity tolerance is commonly associated with whole leaf Na exclusion and maintenance of K homeostasis, but whether spatial ion partitioning among functional leaf compartments contributes to stress adaptation remains unclear. Here, we investigated the relationship between bulk leaf and stomatal complex ionomes and gas exchange performance under salinity using two contrasting genotypes in both maize and faba bean crops. Maize generally maintained higher photosynthesis and stomatal conductance than faba bean under salt stress, which was associated with lower Na accumulation, stronger K retention and distinct ion partitioning patterns between bulk leaf tissue and the stomatal complex. Enrichment analysis revealed that stomatal complex ion composition provided information beyond bulk leaf ion concentrations, with Na and Cl- showing distinct distribution patterns associated with photosynthetic performance. Integrating physiological and ionomic traits further demonstrated that stomatal-complex ion traits captured additional variation in salinity responses. These findings identify the stomatal complex as a functionally distinct ionomic compartment and reveal compartment-specific ion partitioning as an important mechanism underlying species-specific salinity tolerance.

Plant roots exhibit remarkable developmental plasticity, resulting in the adaptation of growth direction and architecture upon environmental changes. Previously, we demonstrated that inorganic phosphate (Pi) triggers Arabidopsis roots to skew to the left when grown on tilted agar plates. This so-called 'phosphate-dependent skewing' (PDS) is caused by a right-handed (clockwise, CW) circumnutation of the root tip, which is driven by a left-handed (counterclockwise, CCW) cell file rotation (CFR) of epidermal cells in the root elongation zone, and involves the cortical microtubule cytoskeleton (Sheng et al., 2024). In the present study, we demonstrate that NaCl triggers a skewing response in the opposite direction and that all other helical movements are also reversed. Thus, 'Salt-Induced Rightward Skewing' (SIRS) is accompanied by a right-handed (CW) epidermal CFR, a left-handed (CCW) circumnutation of the root tip, and hence, a left-handed (CCW) helical root growth. Comparing different Na+- and Cl- salts revealed that SIRS is predominantly caused by cations, and can be induced by K+ and osmotic stress as well, although Na+ is most efficient. To get further insight into the mechanism underlying this response, we tested candidate genes from an earlier GWAS on root responses to salt stress (Deolu-Ajayi et al., 2019) for their potential involvement. This identified GLT1 and DOB1 as being involved in the root skewing response to Pi and NaCl, respectively. Our findings reveal that Pi and salinity elicit opposing effects on root circumnutation, and hence root skewing and growth direction. Understanding the molecular machinery driving this helical behaviour may help explain adaptive mechanisms, including changes in the spatial architecture of roots, and may facilitate the optimization of crop yield under abiotic stress conditions through breeding or crop management strategies. Our results also shed new light on halotropism, which is typically measured as a change in root growth direction to the right, which in the present study has been identified to represent SIRS.

Efficient nutrient and water management is crucial for enhancing crop productivity, soil health, and mitigating environmental losses in cereal cropping systems of semi-arid regions. A two-year field experiment was conducted to evaluate the effects of dairy manure annual application of 50 Mg ha-1 to maintain recommended fertilizer N, compared to sole urea application with two different irrigation regimes (100% and 75% ETc) on crop yield, water use efficiency, deep percolation, nitrate leaching, and soil quality within a wheat-fallow-maize rotation in Pakistan. Suction lysimeters installed at a depth of 1.2 m were used to collect nitrate-N leachates, while HYDRUS-1D was used to assess daily deep percolation losses. Results indicate that the interaction between manure and irrigation was significant for yield, nitrate-N leaching, and soil health. Manure with deficit irrigation showed wheat and maize yield of 4.36 and 7.80 Mg/ha, irrigation water use efficiency (WUEi) of 1.09 and 1.59 kg/ha/mm, respectively, with no significant increase observed with full irrigation; while a significant decrease was observed in the absence of manure, either with full irrigation or deficit irrigation. Manure with deficit irrigation averaged annual nitrate-N leaching of 17.45 kg/ha, while urea and manure with full irrigation averaged 11.46 and 55.59% increases in nitrate-N leaching losses, respectively, without any yield benefits. Our results indicate that deficit irrigation with manure produces optimum yield with reduced nitrate-N leaching risk and improved soil physical properties.

Soybean, a widely cultivated leguminous crop valued for its protein, amino acids, and oil, faces the challenge of maintaining protein levels, which have an inverse correlation with yield. Reducing leaf chlorophyll levels could increase seed protein levels without compromising yield; however, this is yet to be tested. Therefore, to understand the impacts of low chlorophyll mutations on soybean yield and seed composition, we screened and compared 25 low chlorophyll soybean mutants to their 11 dark green parents. PI548210 (Lincoln mutant) demonstrates a higher concentration of protein without affecting yield compared to its dark green parent PI548362 (Lincoln), suggesting it as a good candidate for further large-scale field trials. PI547555 (Y11/y11, Clark mutant) demonstrates a lower concentration of oil without impacting yield, alongside lower gross photosynthesis, but with chlorophyll levels in the pod and seed tissues that are comparable to its dark green parent PI548533 (Clark). These findings are consistent with the oil concentration of the soybean being influenced by pod and seed photosynthesis, which is correlated with pod height and row spacing. Chlorophyll levels in the leaf do not necessarily correlate with those in the pod and seed of low chlorophyll mutants, possibly due to substantially lower expression of chlorophyll synthesis genes in the pod and seed. SIGNIFICANCEO_LIPI548210 (Lincoln mutant), one of twenty-five low chlorophyll soybean mutants, demonstrates a higher concentration of soybean protein without affecting yield compared to its dark green parent (Figure 1 and Table 1). C_LIO_LIPI547555 (Y11/y11, Clark mutant), a low chlorophyll soybean mutant, demonstrates a reduced concentration of soybean oil without impacting yield, alongside lower gross photosynthesis in pod and seed tissues compared to its dark green parent (Figures 3 and Table 2). These findings suggest that the oil concentration of the soybean is influenced by pod and seed photosynthesis, which is in turn influenced by pod height and row spacing (Figure 2). C_LIO_LIChlorophyll levels in the leaf do not necessarily correlate with those in the pod and seed of low chlorophyll mutants, possibly due to substantially lower expression of chlorophyll synthesis genes in the pod and seed (Figure 5-6). C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/744892v1_fig1.gif" ALT="Figure 1"> View larger version (55K): org.highwire.dtl.DTLVardef@4282dcorg.highwire.dtl.DTLVardef@9d565forg.highwire.dtl.DTLVardef@1918292org.highwire.dtl.DTLVardef@1359b1_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 1.C_FLOATNO Two low chlorophyll mutants are as healthy as their dark green parents. Lincoln and its low chlorophyll mutant, left; Clark and its low chlorophyll mutant, known as Y11/y11, right. It can be seen by eye that the plants have low chlorophyll (light green/yellow leaves) but a similar growth habit to their dark green parents. See Supplemental Figures 1-4 for contrast, where low chlorophyll mutants are stunted in growth compared to their dark green parents. C_FIG O_TBL View this table: org.highwire.dtl.DTLVardef@657ec9org.highwire.dtl.DTLVardef@166e75borg.highwire.dtl.DTLVardef@df23c7org.highwire.dtl.DTLVardef@1a60124org.highwire.dtl.DTLVardef@194ed96_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 1.C_FLOATNO O_TABLECAPTIONComparison of seed yield, weight, seed composition between low chlorophyll mutants and their dark green parents. ANOVA is used with linear mixed model (random effect = block, fixed effect = variety). Least squares mean is used to compare. For yield and seed composition, N=4 blocks. For leaf chlorophyll (SPAD), N=40. Yield is average yield per plant (g). n.s. = not significant. C_TABLECAPTION C_TBL O_FIG O_LINKSMALLFIG WIDTH=179 HEIGHT=200 SRC="FIGDIR/small/744892v1_fig3.gif" ALT="Figure 3"> View larger version (26K): org.highwire.dtl.DTLVardef@7a368aorg.highwire.dtl.DTLVardef@192b8f0org.highwire.dtl.DTLVardef@1abb738org.highwire.dtl.DTLVardef@89e978_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 3.C_FLOATNO Light response curve of low chlorophyll mutant (Y11/y11, PI547555) and its parent (Clark, PI548533). Rates of net and gross photosynthesis of low chlorophyll (white) and dark green parents (black) pods under field conditions. Each dot represents a value (n=4) {+/-}SE. We assumed that the seeds greatly inhibited the transmittance of light through the pod and used photosynthetic photon flux density for a single-side. C_FIG O_TBL View this table: org.highwire.dtl.DTLVardef@3f0528org.highwire.dtl.DTLVardef@16ba712org.highwire.dtl.DTLVardef@a5ab2aorg.highwire.dtl.DTLVardef@889254org.highwire.dtl.DTLVardef@3efa4f_HPS_FORMAT_FIGEXP M_TBL O_FLOATNOTable 2.C_FLOATNO O_TABLECAPTIONPod photosynthetic parameters for low chlorophyll mutant (Y11/y11, PI547555) and its parent (Clark, PI548533). Photosynthesis was measured 1 September through 15 September 2021 at the University of Illinois Energy Farm in Urbana, IL, USA. The statistical analysis was done using ANOVA with linear mixed model (alpha=0.05). N=4 {+/-} SEM for Clark and N=3 {+/-} SEM for Y11. C_TABLECAPTION C_TBL O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=130 SRC="FIGDIR/small/744892v1_fig2.gif" ALT="Figure 2"> View larger version (23K): org.highwire.dtl.DTLVardef@a36c26org.highwire.dtl.DTLVardef@1116c8forg.highwire.dtl.DTLVardef@ee5e61org.highwire.dtl.DTLVardef@1766712_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 2.C_FLOATNO Low chlorophyll mutant (Y11/y11, PI547555) and its parent (Clark, PI548533) differ in concentration of seed oil, which interacts with height of pod and row spacing. The box plots show the median (central line), the lower and upper quartiles (box) and the minimum and maximum values (whiskers). The statistical analysis was done using ANOVA with linear mixed model (n=3 blocks, alpha=0.05). Least squares mean is used to compare. N.s., non- significant in the analysis. A. Concentration of oil in low chlorophyll mutant seeds from the upper canopy decreased by 4% compared to the dark green parent (18.2% vs 19%) while there was no difference between them in the seeds from the lower canopy (20.2% vs 20.6%). B. Schematic layout of 2013 field setting showing two different row spacings. C. Concentration of oil in low chlorophyll mutant decreased by 2% in 38cm spacing (21.4% vs 22%) while there was no difference in 19cm spacing (21.3% vs 21.7%) in 2013 field. C_FIG O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=162 SRC="FIGDIR/small/744892v1_fig5.gif" ALT="Figure 5"> View larger version (22K): org.highwire.dtl.DTLVardef@68e508org.highwire.dtl.DTLVardef@94a6ccorg.highwire.dtl.DTLVardef@152a187org.highwire.dtl.DTLVardef@1eae137_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 5C_FLOATNO (greenhouse). Correlation between the level of leaf chlorophyll (x-axis: SPAD reading) and the level of immature pod or seed chlorophyll (y-axis, mg/g DW). Line represents the linear regression model. R-squared is a coefficient of determination, the percentage of the response variable variation that is explained by the linear model. Pod is labeled by the fresh weight of seeds it contained. A. Level of chlorophyll of 25-100mg pod (n=18). B. Level of chlorophyll of 100-200mg pod (n=17) . C. Level of chlorophyll of 25-100mg seed (n=17). D. Level of chlorophyll of 100-200mg seed (n=20). C_FIG O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=180 SRC="FIGDIR/small/744892v1_fig6.gif" ALT="Figure 6"> View larger version (28K): org.highwire.dtl.DTLVardef@167fd88org.highwire.dtl.DTLVardef@361472org.highwire.dtl.DTLVardef@786325org.highwire.dtl.DTLVardef@1b53855_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 6.C_FLOATNO Levels of gene expression in chlorophyll synthesis pathway. A. CHL common pathway genes; Glutamyl-tRNA reductase (GluTR). Glutamate 1- semialdehyde aminotransferase (GSA-AT). ALA dehydratase (ALAD). Uroporphyrinogen III synthase (UROS). Uroporphyrinogen III decarboxylase (UROD). Protoporphyrinogen IX oxidase (PPO). B. Mg branch; Mg-chelatase (Mgch). Magnesium-protoporphyrin IX monomethyl ester cyclase (MPEC). Protochlorophyllide reductase (POR). 3,8-divinyl protochlorophyllide a 8-vinyl-reductase (4VCR). Heme pathway; Ferrochelatase (FECH). Heme oxygenase (HO). Phytochromobilin synthase (HY). Data come from Severin et al (2010). RPKM, reads per kilobase per million mapped reads. DAF, days after flowering. The source seed is experimental line A81-356022 which was generated by introgressing G. soja (PI468916) into G. max (A81-356022). C_FIG

Chloroplasts comprise photosynthesis and other important processes. Plants protect chloroplasts from stresses including Cd accumulation. Common terrestrial plants, excluders apply a set of mechanisms to restrict Cd penetration to chloroplasts. Removal of accumulated Cd from chloroplasts should also be a beneficial strategy. However, we do not know whether excluder plant species have ability to remove Cd from chloroplasts. We used barley as a common excluder plant species. To barley plants, we applied a model with two stable isotopes 111Cd and 114Cd to distinguish Cd accumulated earlier and later. A portion of Cd absorbed by roots continued translocation to shoot for some days after the external source of Cd was changed from one isotope to another. Chloroplasts acquired new portions of Cd and lost part of Cd accumulated earlier; a total Cd content remained rather unchanged. Cd loss from thylakoids was detected in vivo and in vitro. Cd loss from stroma and envelope was observed in vivo but not in vitro. Therefore, barley has at least two distinct mechanisms for Cd removal from chloroplasts: one from thylakoids and another from stroma. We hypothesized diverse chlorophagy pathways as a potential mechanism for Cd removal from chloroplasts. Cd accumulation by chloroplasts was mainly light-independent. In chloroplasts, Cd accumulated in vivo was tightly bound and mainly located in thylakoids. In vitro, chloroplasts from Cd-treated plants accumulated much less Cd than chloroplasts from untreated plants in a previous study. This implies reorganization of transport across chloroplast envelope membranes. HighlightsO_LICd was removed from thylakoids both in vivo and in vitro C_LIO_LICd was removed from stroma and envelope in vivo but not in vitro C_LIO_LIIn chloroplasts, Cd accumulated in vivo was tightly bound C_LIO_LICd accumulation by chloroplasts was mainly light-independent C_LIO_LIRoot barrier slowed down Cd translocation to shoot but not halted it C_LI

Plants make diverse metabolites to outcompete neighboring organisms for space and resources. Some of these toxic metabolites broadly disrupt conserved molecular mechanisms, such as protein biosynthesis. Nonproteogenic amino acids (NPAAs) are a structurally diverse class of metabolites that interfere with protein biosynthesis. The proline (Pro) analog azetidine-2-carboxylic acid (Aze) inhibits plant growth through misincorporation during protein biosynthesis. However, it is unknown if a cascade of downstream stress responses is triggered following Aze misincorporation. Here, we investigate the morphological and stress responses in Arabidopsis grown on Aze. Investigation of root morphological responses show not only reduced root growth, but increased root branching following growth on Aze. Altered root morphology is coupled with a reduced gravitropic response. Aboveground organs were also affected by Aze, including reduced chlorophyll content, reduced photosynthetic efficiency, and increased anthocyanin content. We then tested whether Aze induces reactive oxygen species (ROS) accumulation using multiple approaches and observed both immediate and sustained accumulation of general ROS and H2O2 following treatment with Aze. When plants were grown on Aze supplemented with Pro, ROS levels were restored to normal levels, suggesting that reducing misincorporation events results in less downstream stress responses. In summary, we find that following Aze treatment a cascade of downstream stress responses is induced that exacerbates the effects of toxic NPAAs. This study sheds light on the mechanism of action of NPAAs and provides information on the downstream consequences of translational errors.

Cassava (Manihot esculenta Crantz) is a major staple crop across tropical and subtropical regions. Despite advances in genomic selection, delayed, non-flowering, and asynchronous flowering remain key bottlenecks in breeding programs. To better understand the molecular basis of flowering-time variation, we performed RNA sequencing across three genotypes with contrasting flowering phenotypes (early, late, and non-flowering) sampled at three developmental stages under contrasting light regimes in field conditions (natural light and three-hour night-break with white light). Comparative transcriptomic analysis revealed distinct gene expression patterns associated with flowering responses. Genotype comparisons with no light supplementation revealed stage-specific enrichment of biological processes. Light supplementation was associated with changes in the expression of key components of photoperiodic and circadian regulation, as well as pathways involved in flowering-time integration and hormone and sugar-related signaling. These findings suggest that coordinated changes across multiple biological pathways regulate flowering behavior in cassava. The candidate genes and expression patterns reported provide a foundation for functional studies and advance our understanding of molecular mechanisms governing flowering-time regulation in cassava.

A strategy to improve agricultural water productivity is to increase water use efficiency (WUE) at the level of plant transpiration through genetic selection. This requires detectable genetic variability in WUE and the ability to phenotype and select plants with higher WUE within a population. A proxy for phenotyping leaf level WUE by measuring carbon isotope signature ({delta}13Cleaf) has been supported by theory and data in C4 species. However, the functional relationship of {delta}13Cleaf and WUE in C4 species can be driven by genetics and environment. Therefore, a wide survey of existing natural variation is needed to quantify the heritability and identify various genetic factors that influence {delta}13Cleaf and WUE. In this study a genome-wide association panel was used to quantify the heritability of {delta}13Cleaf. We measured {delta}13Cleaf across a population of 360 genetically diverse lines of the C4 species Sorghum bicolor with single nucleotide polymorphic (SNP) markers determined from whole-genome resequencing. This analysis was conducted on two independent field environments where heritability of {delta}13Cleaf was evident and was driven by small genetic effects from loci that were consistently identified across environments. Candidate genes are presented that offer insights on future targets to manipulate and explore the functional relationship between {delta}13Cleaf and WUEi in C4 plants.

Tomato production, yield and fruit quality face major challenges due to several factors, including the complex polygenic inheritance of agronomically relevant traits, biotic and abiotic stresses, and increasingly stringent regulations limiting the use of phytosanitary products. In this context, bioinoculants have emerged as a sustainable strategy capable of enhancing yield without compromising fruit quality, conferring protection against different stresses and exerting a minimal or no impact on environment and human health. In this study, we evaluated the effects and the underlying mechanisms by which Streptomyces sp. N2A, an actinobacteria isolated from soybean rhizosphere, promotes seed germination, vegetative growth and yield in tomato, without modifying fruit quality. The obtained results demonstrated that the bacterial treatment significantly improved seedlin[g]s emergence and growth and development in vegetative stage. At harvest, yield was also significantly enhanced, mainly driven by increased individual fruit weight, which was positively correlated with a thicker pericarp in fruits from N2A-treated plants. Transcriptional analysis during fruit development revealed a coordinated induction of auxin and cytokinin signaling pathways before and after anthesis, providing a hormonal framework that underlies the promotion of pericarp growth. This study provides evidence of the beneficial effect of inoculation with Streptomyces sp. N2A on tomato yield and constitutes the first report describing the modification of fruit morphology and expression of genes involved in phytohormonal modulation during early growth and development, induced by a plant growth-promoting Streptomyces.

Genetic gains for yield and yield-contributing traits are low or stagnant in sorghum especially under low soil moisture environments which have contributed to a yield gap of 3.0 in Africa. Exploring the extent of variation for yield-determining traits in sorghum will effective variety design to boost production in drought-stressed environments. Therefore, the objective of this study was to determine genetic variability, heritability and genetic gains for agronomic and physiological traits in sorghum under varying drought stress conditions to guide cultivar and trait selection for breeding. The study was conducted as a three-way factorial treatment structure involving a genetically diverse panel of two hundred and twenty-five (225) sorghum genotypes which were grown under three drought conditions [i.e., non-stressed (NS), pre-anthesis drought stress (PrADS), and post-anthesis drought stress (PoADS)] and two environments (e.g., field and glasshouse environments) using a 15 x 15 alpha lattice design in two replicates. Data were collected on agronomic and physiological traits, namely: days to anthesis (DA), days to maturity (DM), plant height (PH), stay-green (SG), seed weight (TKW), biomass yield (BM), harvest Index (HI), grain yield (GY), leaf area (LA), leaf chlorophyll content (SPAD) and stomatal conductance (SC) and subjected to various statistical analyses. Combined analysis of variance showed highly significant (P < 0.001) genotype, drought condition and environment, and their interactions for most traits under assessment. Genotypic coefficient of variation (GCV) was lower than phenotypic coefficient of variation (PCV) for all traits. Heritability in the broad-sense (H2) was moderate for GY (40%) under PrADS condition, but high under NS (60%) and PoADS (65%) conditions. Similarly, high genetic advance was recorded for traits with high heritability. GY positively and significantly correlated with HI under NS (r = 0.88), PrADS (r = 0.62) and PoADS (r = 0.61). Other agronomic and physiological traits poorly correlated with GY. The following genotypes were selected based on high grain yield and suitable agronomic and physiological traits under NS conditions; DAN YARA (5.7 t/ha and SC = 335.5) and JARWA (GY = 5.6 t/ha, SC = 326.3); under PrADS CSRO1 (GY = 2.9 t/ha, SC = 275.2) and ICNSL2014-021-1 (GY = 2.7 t/ha, SC = 268.2) and under PoADS conditions DANYAR BANA (GY = 4.2 t/ha, SC = 237.2) and DAN YARA (3.9 t/ha. SC = 330.0). The selected genotypes with the desirable traits are useful genetic resources for breeding high-performing sorghum hybrids to boost sorghum productivity in drought-prone areas in Africa.