Transcriptional profiling of underground interaction of two contrasting sunflower cultivars with the root parasitic weed Orobanche cumana

Orobanche cumana is an obligate root parasite which specifically infects roots of Helianthus annuus L., causing severe yield and economic losses in agricultural fields worldwide. For an efficient control strategy, it is necessary to understand specialized host defense mechanisms and the pathogenesis of O. cumana during underground interaction with the host. RNA-Seq was used to simultaneously assess the transcriptome of each of two contrasting sunflower cultivars with O. cumana during their post-attachment interactions. Secretome prediction was applied to identify O. cumana proteins from its transcriptome. Infection of O. cumana triggered insufficient defense responses in the susceptible cultivar as compared to the resistant one, probably due to the failure to fully recognize parasite effectors. Secretome prediction from the O. cumana transcriptome enabled robust identification of 180 proteins associated with O. cumana penetration and infection. Functional annotation of these proteins revealed that they were associated with cell wall degradation, nutrient acquisition and pathogenesis. Additionally, a candidate effector containing a PAR1 domain from O. cumana was preliminarily identified as a potential suppressor of plant defense responses. Secretome prediction shed lights on the molecular mechanisms that O. cumana deployed to manipulate host defense. Successful infection of O. cumana inhibited host defense responses and turned host roots from a sink to a source for efficient nutrient flux towards the parasite. In summary, these findings provide insight into the mechanism underlying O. cumana infection and are important in understanding parasitic-host plant interaction.