Planta

Leaf meristem is a cell proliferative zone present in the lateral organ primordia. In this study, we investigated how the proliferative zone affects the final morphology of the lateral organs. We examined how cell proliferative zones differ in the primordia of planar floral organs and polar auxin transport inhibitor (PATI)-treated leaves from normal foliage leaf primordia of Arabidopsis thaliana with a focus on the spatial accumulation pattern of ANGUSTIFOLIA3 (AN3), a key element for leaf meristem positioning. We found that organ shape changes by PATI treatment were correlated to the angle of the cell division plane relative to the leaf primordia axis in the leaf meristem (cell division angle), but not with leaf-meristem positioning, size of the leaf meristem, or the localization pattern of AN3 protein. In contrast, different shapes between sepals and petals compared with foliage leaves were associated with both altered meristem position associated with altered AN3 expression patterns and different distributions of cell division angles. These results suggest that lateral organ shapes are regulated via two aspects: position of meristem and cell division angles Summary statementDifferent lateral organs with different morphology possess different properties of meristems; cell division angles, position of cell proliferative area and AN3 localization patterns.

The physiological status of differentiated somatic plant cells and kinetics of re-entering in cell cycle were investigated in the case of Medicago sativa leaf protoplasts after the application of oxidative stress-inducing agents. Excess copper (30 M) and alloxan (0.5 mM) accelerated cell cycle re-entry at an exogenous auxin concentration that alone was insufficient to induce cell activation. Application of stress-inducing agents accelerated changes in the nuclei landscape with further faster re-entry in DNA replication and cytokinesis. This acceleration was accompanied by a lower level of reactive oxygen species (ROS) accumulations. At later stages, stress-agents treated cells resemble stem cells in planta with a smaller size, higher cell viability, lower ROS level, and lower activities of major ROS scavenging enzymes. A similar cellular response could be achieved by increasing the exogenous auxin concentration. Based on these experimental results, it is suggested that sub-lethal stress treatments evoke a transient cell state that accelerates cellular reprogramming. We also speculate that this transient cell state serves as an effective mechanism for protection against oxidative stress.

We have previously reported that different stresses can lead to substantial DNA methylation changes in strawberry. Here, we wanted to assess the heritability of heat-stress induced DNA methylation and transcriptional changes following asexual and sexual reproduction in a plant. Woodland strawberry (Fragaria vesca) is an ideal model to study epigenetic inheritance in plants because it presents two modes of reproduction: sexual and asexual. Here we wanted to assess if heat-stress induced DNA methylation changes can be transmitted via asexual reproduction and whether past stresses can also affect sexually propagated progenies. Our genome-wide study provides evidence for a memory acquisition and maintenance in F. vesca. We found that certain DNA methylation changes can stably be transmitted over at least three asexual generations. Finally, the first sexual generation by selfing from stressed maternal and their respective non-stressed asexual daughter plants showed both shared and unique stress responses. This suggests that an acquired molecular memory from the previous heat-stress event was transmitted. This molecular memory might be involved in functional plasticity and stress adaption, an important aspects that will have to be investigated in future studies. Finally, these findings may contribute to novel approaches that may contribute to the breeding of climate-ready plants. IN A NUTSHELLO_ST_ABSBackgroundC_ST_ABSWith ongoing climate change, natural plant populations and crops are facing stress situations more frequently and at higher intensity. These unfavorable growing conditions force plants to develop strategies to adapt to persist. One of these strategies involves epigenetic mechanisms which can affect the activity of genes without altering the actual DNA sequence. These molecular modifications can be retained by plants as a molecular "memory" which might be used later to better respond to a stressful event. QuestionIs there multi-generational persistence of heat-stress induced epigenetic patterns in strawberry and are heritable epigenetic changes associated with stress adaptation? FindingsWe found that the strawberry methylome and transcriptome respond with a high level of flexibility to heat-stress. In addition, we took advantage of the two reproductive modes of strawberry (asexual and sexual) to evaluate the acquisition and maintenance of molecular stress memory. We showed how specific DNA methylation and gene expression changes can persist for a long time in progeny plants. We found that the asexual, and seemingly also sexual progenies can retain information in the genome of a past stressful condition that was encountered by its progenitor. Next stepsOur work presents valuable epigenetic and transcriptional screening data to understand plant memory maintenance and transmission over generations. The most important next step will be to assess if heritable stress-induced epigenetic changes can contribute to stress adaptation through a plant competition experiment in natural environments. One sentence summaryStrawberry can transmit molecular stress-memory at the DNA methylation and transcriptional level over multiple generations which may play an important role in stress adaptation.

Maize is a staple food all over the world. Models for climate change suggest that, in the future, cloud formation might be reduced in the tropics increasing the exposure to Ultraviolet-B (UV-B) radiation, a DNA-damaging agent. UV-B (290 to 320 nm) has been shown to affect yield in maize. In this project we have determined the differences in DNA repair efficiencies between U.S. inbred lines B73 and Mo17, and Central American purple landraces from Guatemala and Costa Rica. Our results from single cell electrophoresis experiments (Comet Assay) suggest that the landrace Pujagua Santa Cruz (P1, Costa Rican) was resistant to damage caused by the radiomimetic agent zeocin (24h/100 micrograms per mL), while landrace Pujagua La Cruz (P2, Costa Rican) was able to repair DNA damage after one hour. On the other hand, line Mo17 (Missouri, USA) was unable to repair the damage, while B73 (Iowa, USA) and the landraces Jocopilas (Guatemalan), Orotina Congo (Costa Rican) and Talamanca (Costa Rican) were partially able to repair DNA damage. High Resolution Melting (HRM) curve analysis of putative homologous DNA repair gene ZeaATM1 showed that both P1 and P2 had differences in the melting temperatures for this gene compared to B73 and Mo17, while P1 showed additional differences in ZeaSOG1, ZeaRAD51 and ZeaBRCA1, suggesting that in this landrace the presence of polymorphisms may be common among key genes for this pathway. Taken together our results suggest that key adaptive differences in DNA repair efficiencies exist between inbred lines and landraces of maize and that some Central America landraces could be used as a valuable pool of alleles for plant breeding aiming to increase tolerance to radiation.

Understanding the molecular basis of plant heat tolerance helps to predict the consequences of climate warming on plant performance, particularly in vulnerable environments. Our current understanding comes primarily from studies in Arabidopsis thaliana (Arabidopsis) and select crops exposed to short and intense periods of heat stress. In this study we sought to characterise the transcriptomic responses of Wahlenbergia ceracea (W. ceracea), an Australian alpine herb, to growth under sustained moderate warming. We compared responses of pre-defined tolerant and sensitive lines, based on measures of photosynthetic thermostability, to growth under cool (24/15 {degrees}C day/night) or warm (30/20 {degrees}C day/night) temperatures to identify the pathways involved in heat tolerance and acclimation. Under warmer growth temperatures, W. ceracea up-regulated genes involved in RNA metabolism, while down-regulating those involved in photosynthesis and pigment metabolism. In tolerant lines, genes related to photosystem II and light-dependent photosynthetic reactions were more strongly down- regulated. This suggests that the regulation of electron transport and its components may be involved in thermal acclimation. Our results also highlight the importance of hormonal gene networks, particularly those responsive to ethylene, during longer-term moderate warming. In conclusion, our results point to post-transcriptional processes and the stabilisation of the electron transport chain as candidate mechanisms for thermal acclimation in heat-tolerant W. ceracea. The study also revealed many temperature-responsive genes with no detectable ortholog in Arabidopsis, whose characterization may enhance our understanding of physiological acclimation and have relevance for the biotechnological improvement of threatened species and crops.

O_LIBackground and Aims Germination is a vital stage in a plants life cycle, and a different germination behavior of offspring in comparison to their parents can have fitness consequences. In studies on hybridization between Rhinanthus minor and R. major, low germination rates of F1 hybrids with R. major as the maternal parent have often been reported. In contrast, the F1m hybrid, with R. minor as the maternal parent, germinates readily and rapidly. C_LIO_LIMethods In order to find the cause of this difference, we used RNA-Seq to obtain transcriptome profiles of F1a and F1m seeds during stratification at 4{degrees}C and just after germination, after 40 days of stratification for the F1m seeds and 60 days for the F1a seeds. C_LIO_LIKey Results A comparison of the transcriptome of F1a seeds that had just germinated (60 days) with non-germinated F1a seeds after 40 and 60 days revealed 2918 and 1349 differentially expressed (DE) genes, respectively. For F1m seeds, 958 genes showed differential expression in germinated and non-germinated seeds after 40 days. The DE genes of F1a and F1m hybrids clustered into two separate groups, even though they had the same parents, and no differentially expression was found for plastid genes. Non-germinated F1a seeds had an abundance of enzymes and proteins associated with peroxidase activity, peroxiredoxin activity and nutrient reservoir activity. Expression of genes related to seed germination and seed development increased in non-germinated F1a hybrid seeds between 40 and 60 days of cold stratification. F1a seeds that had germinated showed an upregulation of genes related to the gibberellic acid-mediated signaling pathway and response to gibberellin, along with a low expression of DELLA superfamily. C_LIO_LIConclusions Although the results demonstrated strong differences in gene expression during stratification between the reciprocal hybrids, we could not identify its cause, since no plastid genes were differentially expressed. It is possible that differences in embryo development after seed formation and before stratification play a role, including epigenetic imprinting. C_LI

Published studies have reported species-variance between profiles of Calvin-Benson cycle (CBC) intermediates, not only between C4 species and C3 species, but also within C3 species (Arrivault et al., 2019, Borghi et al. 2019). It was proposed that this variance reflects lineage-dependent changes in the balance between different reactions, or poising, of the CBC. These earlier studies investigated phylogenetically-unrelated C3 species. In the current study, CBC intermediates were profiled in five closely-related species from Solanum sect. lycopersicon subsect. Lycopersicum. The levels of individual CBC intermediates showed many significant differences. In a principal component analysis, whilst three species (Solanum lycopersicum, Solanum cheesmaniae, Solanum neorickii) overlapped, Solanum pimpinellifolium and especially Solanum pennellii grouped separately, and were at opposing ends of the distribution. When combined with published data, whilst the separation between Solanum species was retained, they formed a group that was separated from five other C3 species, as well as two C4 species. It is discussed that the observed variation in CBC metabolites profiles within Solanum, together with their separation from other C3 species, supports the idea that CBC evolution is shaped both by phylogenetic relatedness and lineage-specific adaptation. HighlightVariance of intermediate levels points to poising of the Calvin-Benson cycle varying between closely-related species in the tomato clade Solanum sect. lycopersicon subsect. Lycopersicum

Currently, the role of reactive oxygen species (ROS) in plant growth is a topic of interest. In this study, we discuss the role of ROS in cell division. We analyzed ROS impact on the stiffness of plant cell walls and whether ROS play an important role in Brassica napus ability to adapt to cold stress. Cultivated sterile seedlings and calli of cold-tolerant cultivar 16NTS309 were subjected to cold stress at 25{degrees}C and 4{degrees}C, respectively. Under normal conditions, O2.- mainly accumulated in the leaf edges, shoot apical meristem, leaf primordia, root tips, lateral root primordia, calli of meristematic nodular tissues, cambia, vascular bundles and root primordia, which are characterized by high division rates. After exposure to cold stress, the malondialdehyde and ROS (O2.-) contents in roots, stems and leaves of cultivar 16NTS309 were significantly higher than under non-cold conditions (P < 0.05). ROS (O2.-) were not only distributed in these zones, but also in other cells, at higher levels than under normal conditions. A strong ROS-based staining appeared in the cell wall. The results support a dual role for apoplastic ROS, in which they have direct effects on the stiffness of the cell wall, because ROS cleave cell-wall, and act as wall loosening agents, thereby either promoting or restricting cellular division. This promotes the appearance of new shoots and a strong root system, allowing plants to adapt to cold stress.

DICER-LIKE (DCL) proteins have a central role in plant small RNA (sRNA) biogenesis. The Marchantia polymorpha genome encodes four DCL proteins: two DCL1 homologs, MpDCL1a and MpDCL1b, MpDCL3 and MpDCL4. While MpDCL1a, MpDCL3 and MpDCL4 show high similarities to their orthologs in Physcomitrium patens and Arabidopsis thaliana, MpDCL1b shares only a limited homology with PpDCL1b, but it is very similar, in terms of functional domains, to orthologs in Anthoceros agrestis and Salvinia cucullata. We generated Mpdclge mutant lines via the CRISPR/Cas9 system and performed comprehensive phenotypic analyses of these mutant lines, under control and salt stress conditions as well as upon exogenous naphthaleneacetic acid (NAA) and abscisic acid (ABA) treatments to gain insights into the respective MpDCL functions. While Mpdcl1age mutants display severe developmental aberrations throughout their development, no adverse phenotypic changes are detectable in Mpdcl1bge and Mpdcl4ge mutants except the development of less and smaller male sexual organs (antheridiophores) when they are cultivated under photoperiod conditions supplemented with far-red light. Mpdcl3ge mutants display rosette-shaped thallus formation and overall faster development, but are not able to form antheridiophores. The rosette-shaped thallus development of Mpdcl3ge can be reverted to a wild-type-like thallus growth upon NAA treatment. Mpdcl1bge mutants can tolerate high levels of salt, whereas Mpdcl4ge mutants show higher salt sensitivity. Moreover, Mpdcl1age and Mpdcl3ge mutants show an ABA-hypersensitive phenotype. It can be concluded that the observed phenotypic alterations, under normal or treatment conditions, are linked to the mutations in the respective MpDCLs and hence to defective or altered sRNA biogenesis pathways in M. polymorpha. In conclusion, MpDCLs and their associated sRNAs regulate development, abiotic stress and phytohormonal response in M. polymorpha.

BackgroundControlled degradation of genomic DNA is a common phenomenon observed in all known cases of programmed cell death (PCD) in both animals and plants. In plants, nucleic acid degradation during PCD facilitates the redistribution of their constituent building blocks. Previous studies have shown that nucleases from the S1/P1 family are involved in this process; however, due to its complexity, it has been hypothesized that nucleases from other families, including staphylococcal-like nucleases (SNc), may also participate. In Arabidopsis, this family comprises two nucleases with an atypical plasma membrane localization for this type of enzymes: AtCAN1 and AtCAN2. ResultsUsing the promoter-driven GUS reporter assay, we showed that the genes encoding SNc nucleases are expressed in tissues that can be grouped into three main categories. The first category includes plant structures that are clear examples of organs undergoing PCD, such as the root cap, vascular bundle elements, the tapetum, maturing seed pods, and senescent leaves. The second category comprises cells whose function involves interaction with the external environment and which are susceptible to pathogen attack. This group includes root hairs, stomatal guard cells, and hydathodes. The third group of plant structures showing SNc nuclease activity consists of elements characterized by endoreduplication, i.e., stipules, trichomes, and the basal parts of the hypocotyl. ConclusionsOur studies show that SNc nucleases are as broadly involved in the DNA degradation during plant PCD as the previously reported S1/P1 proteins. The frequent overlap in their expression profiles suggests cooperative action. Whereas SNc nucleases localize to the plasma membrane, S1/P1 nucleases are nuclear, indicating distinct yet complementary nucleolytic pathways. We further demonstrate that SNc nucleases are specifically expressed in organs not undergoing PCD but characterized by endoreduplication, implicating them in an unexplored mechanism for redistributing polyploid DNA components.

Papaya (Carica papaya Linn.) is a tropical plant whose draft genome has been sequenced. Papaya produces large fruits rich in vitamins A and C and is an important cash crop in developing countries. Nonetheless, little is known about how the female gametophyte develops, how it is fertilized and how it develops into a mature seed containing an embryo and an endosperm. The Papaya female gametophyte displays a Polygonum-type architecture consisting of two synergid cells, an egg cell, a central cell, and three antipodal cells. Reports are available of the presumed existence of varieties in which cross fertilization is bypassed and autonomous development of embryos occurs (e.g., apomixis). In this study, we analyzed the development of female gametophytes in a commercial Hawaiian parental line and in the presumed apomictic Costa Rican line L1. Samples were collected before and after anthesis to compare the overall structure, size and transcriptional patterns of several genes that may be involved in egg and endosperm cell fate and proliferation. These genes were the putative papaya homologs of ARGONAUTE9 (AGO9), MEDEA (MEA), RETINOBLASTOMA RELATED-1 (RBR1), and SLOW WALKER-1 (SWA1). Our results suggest that its feasibly to identify structural features of Polygonum-type development, and that in bagged female flowers of line L1 we might have observed autonomous development of embryo-like structures. Possible downregulation of papaya homologs for AGO9, MEA, RBR1 and SWA1 was observed in embryo sacs from line L1 before and after anthesis, which may suggest a link between suspected apomixis and transcriptional downregulation of genes for RNA-directed DNA methylation, histone remodelers, and rRNA processing. Most notably, the large size of the papaya embryo sac suggests that it could be a cytological alternative to Arabidopsis thaliana for study. Significant variation in embryo sac size was observed between the varieties under study, suggesting wide differences in the genetic regulation of anatomical features.

O_LIRoot hair growth is tuned in response to the environment surrounding plants. While most of previous studies focused on the enhancement of root hair growth during nutrient starvation, few studies investigated the root hair response in the presence of excess nutrients. C_LIO_LIWe report that the post-embryonic growth of wild-type Arabidopsis plants is strongly suppressed with increasing nutrient availability, particularly in the case of root hair growth. We further used gene expression profiling to analyze how excess nutrient availability affects root hair growth, and found that RHD6 subfamily genes, which are positive regulators of root hair growth, are down-regulated in this condition. C_LIO_LIOn the other hand, defects in GTL1 and DF1, which are negative regulators of root hair growth, cause frail and swollen root hairs to form when excess nutrients are supplied. Additionally, we observed that the RHD6 subfamily genes are mis-expressed in gtl1-1 df1-1. Furthermore, overexpression of RSL4, an RHD6 subfamily gene, induces swollen root hairs in the face of a nutrient overload, while mutation of RSL4 in gtl1-1 df1-1 restore root hair swelling phenotype. C_LIO_LIIn conclusion, our data suggest that GTL1 and DF1 prevent unnecessary root hair formation by repressing RSL4 under excess nutrient conditions. C_LI

Plants possess well-developed light sensing mechanisms and signal transduction systems for regulating photomorphogenesis. ELONGATED HYOCOTYL 5 (HY5), a basic leucine zipper transcription factor, has been extensively characterized in dicot plants. In this study, we have shown that OsbZIP1 is a functional homolog of Arabidopsis HY5 (AtHY5) and is important for light-mediated regulation of seedling and mature plant development in rice. Ectopic expression of OsbZIP1 in rice reduces plant height and leaf length without affecting plant fertility, which is in contrast to OsbZIP48, another HY5 homolog we characterised earlier. OsbZIP1 is alternatively spliced and the isoform OsbZIP1.2 lacking COP1 binding domain regulates seedling development in dark; this is unique since AtHY5 lacking COP1 binding domain does not display such a phenotype. Rice seedlings overexpressing OsbZIP1 were found to be shorter than vector control under white and monochromatic light conditions whereas RNAi seedlings displayed completely opposite phenotype. While OsbZIP1.1 is light regulated, OsbZIP1.2 shows similar protein profile in both light and dark conditions. Due to its interaction with OsCOP1, OsbZIP1.1 undergoes degradation via 26S proteasome under dark conditions. Also, OsbZIP1.1 interacts with CASEIN KINASE 2 (OsCK2[a]3) and consequently undergoes phosphorylation. In comparison, OsbZIP1.2 did not show any interaction with COP1 and OsCK2[a]3. We propose that OsbZIP1.1 most likely works under low fluence of blue light (15 mol/m{superscript 2}/s) while OsbZIP1.2 becomes dominant as the fluence is increased to 30 mol/m{superscript 2}/s. Data presented in this study reveal that AtHY5 homologs in rice have undergone neofunctionalization and alternative splicing (AS) of OsbZIP1 has increased the repertoire of its functions. One sentence summaryAlternative spliced forms of OsbZIP1, an AtHY5 homolog in rice, regulate seedling development in response to light and dark

- Plant architecture is controlled by several endogenous signals including hormones and sugars. However, only little is known about the nature and roles of the sugar signalling pathways in this process. Here we test whether the sugar pathway mediated by HEXOKINASE1 (HXK1) is involved in the control of shoot branching. - To test the involvement of HXK1 in the control of shoot architecture we modulated the HXK1 pathway using physiological and genetic approaches in diverse plants, rose, arabidopsis and pea and evaluated impacts of hormonal pathways. - We show that triggering a hexokinase-dependent pathway was able to promote bud outgrowth in pea and rose. In arabidopsis, both HXK1 deficiency and defoliation led to decreased shoot branching and conferred hypersensitivity to auxin. HXK1 expression was positively correlated with sugar availability. HXK1-deficient plants displayed decreased cytokinin levels and increased expression of MAX2 which is required for strigolactone signalling. The branching phenotype of HXK1-deficient plants could be partly restored by cytokinin treatment and strigolactone deficiency could override the negative impact of HXK1 deficiency on shoot branching. - Our observations demonstrate that a HXK1-dependent pathway contributes to the regulation of shoot branching and interact with hormones to modulate plant architecture.

Hybridization and introgression between cork oak (Quercus suber) and holm oak (Q. ilex) have traditionally been reckoned as undesirable processes, since hybrid individuals lack the profitable bark characteristics of cork oak. Nevertheless, a systematic and quantitative description of the bark of these hybrids at the microscopic level based on a significant number of individuals was not available to date. In this work we provide such a qualitative and quantitative description, identifying the most relevant variables for their classification. Hybrids show certain features intermediate between those of the parent species, as well as other unique features, as the general suberization of inactive phloem, reported here for the first time. These results suggest a relevant hybridization-induced modification of the genetic expression patterns. Therefore, hybrid individuals provide a valuable material to disentangle the molecular mechanisms underpinning bark development in angiosperms.

ContextAbiotic stress, and particularly drought, is a major threat to plant growth generally and world food security specifically and it is important for humanity to come up with ways to reduce the impact of drought and abiotic stress on plant growth. This is particularly important in the context of global climate change. Earlier research by a range of researchers has hinted that the use of cheap citric acid in treating plants may induce enhanced stress response pathways which may assist in enhancing drought tolerance. However, how altered stress response pathways affect plant growth patterns, and how these may affect drought tolerance, has not been well researched. MethodsSpotted Gum seedlings were grown with and without initial treatment with citric acid, and with and without simulated drought. Key resultsTreatment with citric acid resulted in plants growing larger and more fibrous root systems compared to control plants. The effect was stronger under moderate drought. ImplicationsExogenous treatment of cotyledon roots with citric acid has tremendous potential for enhancing plant root systems under moderate drought. Resulting enhanced root systems could be expected to enhance a plants access to soil water and thus improve drought tolerance. Reduced shoot to root ratios could also be expected to improve drought tolerance of young plants in the early growth phase. SummaryIn addition to potentially having a negative effect on mine revegetation drought remains one of the major causes of agricultural loss globally, threatening food security. A range of research has hinted at the role of citric acid in plant stress response and particularly in drought tolerance (Godbold et al. 1984; Shlizerman et al. 2007; Sun and Hong 2011). It was reported that Arctic tundra soils contain high levels of citric acid (Jones 1998). Jones posed the question as to the relevance of citric acid in plant stress response and particularly to drought tolerance in environments where liquid water is limited. In order to discover whether citric acid might be used to enhance plant growth patterns leading to enhanced drought tolerance in woody species used in large scale mine rehabilitation, a series of trials were established. In these, the roots of cotyledons of commonly used species including Spotted Gum (Corymbia maculata) were soaked in various concentrations of citric acid in order to examine the effect on early plant growth. This paper discusses the results of one of these experiments conducted at the University of Newcastle as part of the authors PhD program. A range of responses were noted in treated seedlings including the development of larger and more fibrous root systems. This response was stronger in plants subject to moderate drought and suggested that treatment enhanced an existing stress response pathway that affected root growth. This significantly enhanced root effect had not been previously noted in response to treatment with citric acid. Other beneficial effects were noted including the enhancement of shoot to root ratio and subsequent enhanced shoot growth as a result of larger and more fibrous root systems. Results from the study raised the question as to how widespread these effects are in the broader plant kingdom and what might be the relevance to food crop production? In this context, further research was undertaken on seeds and tissue culture of key crop species and the results, including significant effects on leaf gas exchange, and this will be reported in later papers. As such, it should be noted that this paper is part of a much larger research program in which the effect of citric acid treatment on cotyledons, seed and tissue culture of a range of woody C3 species is examined. Summary text for journal table of contentsDrought, induced through global climate change and other factors, is likely to cause major conflict through its effect on plant establishment and food security in particular. Using Australian Spotted Gum trees as a subject, this experiment shows that the use of cheap citric acid on seedlings can produce growth effects such as enhanced fibrous root growth that, among other benefits, may make them significantly more drought-tolerant. The results may be beneficial to commercial forestry but may also have major implications for food security worldwide if observed effects are relevant to food crop species. Table of contents graphic O_FIG O_LINKSMALLFIG WIDTH=177 HEIGHT=200 SRC="FIGDIR/small/513958v1_ufig1.gif" ALT="Figure 1"> View larger version (126K): org.highwire.dtl.DTLVardef@947a3org.highwire.dtl.DTLVardef@13e4347org.highwire.dtl.DTLVardef@b31817org.highwire.dtl.DTLVardef@1f29170_HPS_FORMAT_FIGEXP M_FIG C_FIG

Triterpene saponins (TS) are a structurally diverse group of metabolites that are widely distributed in plants. They primarily serve as defense compounds and their production is often triggered by biotic stresses through signaling cascades that are modulated by phytohormones such as the jasmonates (JA). Two JA-modulated basic helix-loop-helix (bHLH) transcription factors (TFs), TRITERPENE SAPONIN BIOSYNTHESIS ACTIVATING REGULATOR 1 (TSAR1) and TSAR2, have been previously identified as direct activators of TS biosynthesis in the model legume Medicago truncatula. Here, we report on the involvement of the core endoplasmic reticulum (ER) stress basic leucine zipper (bZIP) TFs bZIP17 and bZIP60 in the regulation of TS biosynthesis. Expression and processing of M. truncatula bZIP17 and bZIP60 proteins was altered in roots with perturbed TS biosynthesis or treated with JA. Accordingly, such roots displayed an altered ER network structure. M. truncatula bZIP17 and bZIP60 proteins were shown to be capable of interfering with the TSAR-mediated transactivation of TS biosynthesis genes, particularly under ER stress conditions, when they translocate from the ER to the nucleus. Furthermore, the inhibitory role of ER stress bZIP TFs in the regulation of JA-dependent terpene biosynthetic pathways appears to be widespread in the plant kingdom, as we demonstrate that it also occurs in the regulation of monoterpene indole alkaloid biosynthesis in the medicinal plant Catharanthus roseus. We postulate that activation of ER stress bZIP TFs provides the plant with a mechanism to balance metabolic activities and thereby adequately govern modulation of growth, development and defense processes in defined stress situations. One sentence summaryER stress bZIP transcription factors can interfere with the activity of jasmonate-inducible bHLH transcription factors to modulate the elicitation of plant specialized metabolism in stress conditions.

Hormesis refers to the adaptive mechanism of organisms in response to environmental challenges where a lower dose of a toxic compound induce an improvement in functionality and overall development and a higher dose endangers even the existence of the organism. The recent developments in hormetic studies are of paramount importance in plant research as they help in risk assessment of environmental contaminants, protect the vegetation against pollution, and improve crop productivity. As one of the most toxic contaminants, cadmium is considered to have detrimental effects on the growth and development of plants. However, recent studies have revealed the beneficial effects of cadmium in plants at low levels of exposure however the exact mechanism behind this phenomenon is poorly deciphered. In this study, we have focused on observing the response of tomato seedlings under different concentrations of cadmium. The morphological, biochemical, and histochemical characterization of these seedlings under low cadmium exposure has confirmed their hormetic effects. The differential gene expression by transcriptomic profiling in low cadmium showed that, apart from genes involved in oxidoreductase activity, and signaling, several lncRNAs, also differentially expressed. The lncRNAs are known to regulate gene expression on the chromatin level and post-transcriptional regulation. First time we are reporting the expression of lncRNAs in hormesis as important factor for enhanced growth. In-silico analysis revealed the functions of lncRNAs, involving the prediction of cis-targets, mi-RNA precursors, and their targets. Two miRNAs; sly-MIR396a and sly-MIR1063g were seen to have a direct role in improving the growth of plants treated with low cadmium provided an insight into the molecular mechanisms of their role in cadmium hormesis. These findings provided important understanding of the molecular basis of the hormetic phenomenon which can pave a path for generating crops with improved agronomic characteristics. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=149 SRC="FIGDIR/small/663119v1_ufig1.gif" ALT="Figure 1"> View larger version (27K): org.highwire.dtl.DTLVardef@8de5b0org.highwire.dtl.DTLVardef@1e2ad13org.highwire.dtl.DTLVardef@d0f7e2org.highwire.dtl.DTLVardef@14238b3_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LILow cadmium exposure on Solanum lycopersicum seedlings showed more promising outcomes in terms of growth and development. C_LIO_LIThe plants exposed to 1{micro}M Cd treatment continued to exhibit superior growth responses despite removing the cadmium from the media after 5 days of treatment. C_LIO_LIThe GO analysis of Differentially Expressed Genes (DEGs) suggested several lncRNAs differentially expressed in 1 {micro}M Cd condition. C_LIO_LIDifferentially expressed LncRNAs Solyc01g006780.4 and Solyc12g019150.1 generated the miRNAs, sly-MIR396a and sly-MIR1063g respectively. C_LIO_LIUpregulation of sly-MIR396a and sly-MIR1063g resulted in the downregulation of GRF12 and NET4B-like proteins respectively leading to increased growth of tomato plants. C_LI

O_LIReactive oxygen species (ROS) regulate plant growth, development, and responses to the environment. ROS production by the RESPIRATORY BURST OXIDASE PROTEIN D (RBOHD) protein was recently shown to be regulated by PHYTOCHROME B (phyB), and phyB was found to be phosphorylated by FERONIA, highlighting the possibility that these three proteins interact to regulate ROS levels during stress. C_LIO_LIImmunoprecipitation and proximity labelling, followed by split-luciferase and functional validation assays, were used to study the interactions between FERONIA, phyB, and RBOHD during excess light (EL) stress in Arabidopsis thaliana. C_LIO_LIWe reveal that phyB and FERONIA interact with RBOHD, that phosphorylation of phyB by FERONIA, as well as the kinase activity of FERONIA, are required for RBOHD-driven ROS production in response to EL stress, and that CYSTEINE-RICH RECEPTOR LIKE KINASE 10 (CRK10) and PLASMA MEMBRANE INTRINSIC PROTEIN 2;6 (PIP2;6) interact with RBOHD and phyB and are also required for EL-driven RBOHD ROS production. C_LIO_LIOur findings uncover the existence of a putative plasma membrane complex between FERONIA, RBOHD, CRK10, and PIP2;6 that interacts with phyB to regulate ROS production in Arabidopsis in response to stress. This complex could play a canonical role in the integration and regulation of multiple signaling pathways in plants. C_LI Plain Language SummaryWe identified a complex between several different proteins at the plasma membrane that interacts with the light and temperature receptor protein phytochrome B to regulate reactive oxygen species formation during stress in plants. This complex could be involved in the regulation and integration of multiple abiotic and biotic signals in plants. tenten

Anthocyanins are flavonoids responsible for the color of berries in skin-pigmented grapevine (Vitis vinifera L.). Due to the widely adopted vegetative propagation of this species, somatic mutations occurring in meristematic cell layers can be fixed and passed into the rest of the plant when cloned. In this study we focused on the transcriptomic and metabolic differences between two color somatic variants. Using microscopic, metabolic and mRNA profiling analyses we compared the table grape cultivar (cv.) Red Globe (RG, with purplish berry skin) and cv. Chimenti Globe (CG, with a contrasting reddish berry skin color). As expected, significant differences were found in the composition of flavonoids and other phenylpropanoids, but also in their upstream precursors shikimate and phenylalanine. Among primary metabolites, sugar phosphates related with sucrose biosynthesis were less accumulated in cv. CG. The red-skinned cv. CG only contained di-hydroxylated anthocyanins (i.e. peonidin and cyanidin) while the tri-hydroxylated derivatives malvidin, delphinidin and petunidin were absent, in correlation to the reddish cv. CG skin coloration. Transcriptomic analysis showed alteration in flavonoid metabolism and terpenoid pathways and in primary metabolism such as sugar content. Eleven flavonoid 35-hydroxylase gene copies were down-regulated in cv. CG. This family of cytochrome P450 oxidoreductases are key in the biosynthesis of tri-hydroxylated anthocyanins. Many transcription factors appeared down-regulated in cv. CG in correlation to the metabolic and transcriptomic changes observed. The use of molecular markers and its confirmation with our RNA-seq data showed the exclusive presence of the null MYBA2 white allele (i.e. homozygous in both L1 and L2 layers) in the two somatic variants. Therefore, the differences in MYBA1 expression seem sufficient for the skin pigmentation differences and the changes in MYBA target gene expression in cv. Chimenti Globe.