A transcriptome atlas of Striga hermonthica germination

Societal Impact StatementWitchweeds, parasitic plants of the genus Striga, are nicknamed "cereal killers" because of their devasting destruction of Africas most staple cereals, including maize, sorghum, millets, and upland rice. The parasite relies on biomolecules emitted from the host roots to germinate and therefore initiate its infectious lifecycle. Some sorghum varieties have evolved to not produce effective germination stimulants, making them resistant to the parasite. Here, we assess genetic factors that underpin Striga germination. We discuss how such knowledge can be used to develop new Striga management strategies through the disruption of host-parasite communication exchange. SummaryO_LISeeds of the parasitic plant Striga are dormant. They only germinate in response to biomolecules emitted from the hosts root exudate, strigolactones (SL). But, it is now emerging that Striga germination is a much more complex process regulated by crosstalk of hormone signaling pathways. C_LIO_LITo further understand the genetic basis of the communication exchange between Striga and its host sorghum, we performed a comparative transcriptomic analysis. We sought to identify major transcriptomic changes that define the germination process in Striga and a set of genes that may contribute to the differences in germination rates. C_LIO_LIResults showed that germination proceeds immediately after SL perception and is marked by a wave of transcriptional reprogramming to allow for metabolic processes of energy mobilization. Cluster analysis using self-organizing maps (SOMs) revealed a time-phased and genotype-differentiated response to germination stimulation. The variation in germination was also a function of hormonal crosstalk. The early germination stage was associated with significant repression of genes in the abscisic acid (ABA) biosynthesis pathway. Other hormones influenced germination as follows: (i) ABA and auxin repressed germination, (ii) brassinosteroid, ethylene and jasmonic acid promoted germination, and (iii) cytokinin had a more prominent role post-germination rather than during germination. Perception of SL sets the germination programme leading to different rates of germination in sorghum followed by a complex hormonal regulation network that acts to either repress or enhance germination. These results have far-reaching implications for developing Striga management strategies by disrupting hormonal communication exchange. C_LI