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Key message: The HaOr5 resistance gene is located in a large genomic insertion containing putative resistance genes and provides resistance to O. cumana, preventing successful connection to the sunflower root vascular system. Orobanche cumana (sunflower broomrape) is a parasitic plant that is part of the Orobanchaceae family and specifically infests sunflower crops. This weed is an obligate parasitic plant that does not carry out photosynthetic activity or develop roots and is fully dependent on its host for its development. It produces thousands of dust-like seeds per plant. It possesses a high spreading ability and has been shown to quickly overcome resistance genes successively introduced by selection in cultivated sunflower varieties. The first part of its life cycle occurs underground. The connection to the sunflower vascular system is essential for parasitic plant survival and development. The HaOr5 gene provides resistance to sunflower broomrape race E by preventing the connection of O. cumana to the root vascular system. We mapped a single position of the HaOr5 gene by quantitative trait locus mapping using two segregating populations. The same location of the HaOr5 gene was identified by genome-wide association. Using a large population of thousands of F2 plants, we restricted the location of the HaOr5 gene to a genomic region of 193 kb. By sequencing the whole genome of the resistant line harboring the major resistance gene HaOr5, we identified a large insertion of a complex genomic region containing a cluster of putative resistance genes. [ABSTRACT FROM AUTHOR]

Aims: 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. Methods: 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. Results: 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. Conclusions: 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. [ABSTRACT FROM AUTHOR]