A transcriptome atlas ofStriga hermonthicagermination

Abstract

AbstractSocietal Impact StatementWitchweeds, parasitic plants of the genusStriga, are nicknamed “cereal killers” because of their devasting destruction of Africa’s 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 underpinStrigagermination. We discuss how such knowledge can be used to develop newStrigamanagement strategies through the disruption of host-parasite communication exchange.SummarySeeds of the parasitic plantStrigaare dormant. They only germinate in response to biomolecules emitted from the host’s root exudate, strigolactones (SL). But, it is now emerging thatStrigagermination is a much more complex process regulated by crosstalk of hormone signaling pathways.To further understand the genetic basis of the communication exchange betweenStrigaand its host sorghum, we performed a comparative transcriptomic analysis. We sought to identify major transcriptomic changes that define the germination process inStrigaand a set of genes that may contribute to the differences in germination rates.Results 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 developingStrigamanagement strategies by disrupting hormonal communication exchange.