Mots-Clés
Parasitic plants
seed germination
comparative transcriptomics
time-course RNAseq
Description
Broomrapes (Orobanche and Phelipanche spp., Orobanchaceae family) are obligate root-parasitic weeds causing severe yield losses on many crops, including sunflower and oilseed rape in France. Their survival relies on a tight synchronization with the host: seeds germinate only after perceiving germination stimulants (GS) exuded by host roots. These GS are chemically diverse and species-dependent: strigolactones for most broomrapes, but also isothiocyanates for Phelipanche ramosa populations adapted to oilseed rape, sesquiterpene lactones for Orobanche cumana (sunflower broomrape), or still-unknown molecules for O. hederae (ivy broomrape). They are perceived by a family of divergent KAI2 receptors (KAI2d), which has expanded independently in each species, and germination ultimately requires the induction of the ABA-catabolic gene CYP707A. Between perception and CYP707A activation, however, the signaling events remain largely unknown. A key question is whether chemically unrelated GS, perceived by different receptors in different species, converge on a common signaling pathway or activate distinct, species- and stimulant-specific responses. This internship is part of a broader ANR project aiming to decipher the diversity of GS perception and of the molecular actors recruited during the signaling pathway that leads to broomrape seed.
The aim of the internship is to identify convergent and divergent transcriptional signatures of germination across broomrape species and stimulants, using a comparative time-course RNA-seq approach. The intern will first characterize the temporal dynamics of the transcriptional response of seeds to their GS in P. ramosa, O. cumana and O. hederae. These responses will then be compared in order to distinguish a core response, shared by all species and stimulants, from species-specific and stimulant-specific responses. Finally, this comparison will highlight candidate regulators of the germination pathway, with a particular focus on the KAI2/MAX2/SMXL signaling module, transcription factors and CYP707A.