Orobanche cumana (sunflower broomrape) is an obligate parasitic plant that specifically infects sunflower (Helianthus annuus). It is one of the main limiting factors of sunflower crop in Eastern Europe, Spain and Asia. In 2007, the first infested fields have been reported in France. Breeding for resistance in sunflower was successful but new more virulent races of O. cumana often overcame the resistance genes. The first developmental stages of O. cumana occur underground. The germination of the seeds is first stimulated by sunflower root exudates before entering the host root through a haustorium. Without roots nor chlorophyll, O. cumana depends on sunflower for water and nutrients supply. It connects to the vascular system of the sunflower root and store metabolites in a tubercle before emerging a flowering shoot. The inactivation of these developmental stages is a key resistance mechanism in sunflower. A better understanding of the biology of O. cumana will help to identify new resistance processes and resistance genes in sunflower. In the frame of a collaborative project between French and Spanish research institutes, we have produced a first version of the 1.42 Gb genome sequence of O. cumana by combining PacBio sequencing, optical mapping and genetic map. More than twenty transcriptomic RNA-seq experiments from O. cumana were used for annotating the genome sequence. This first sequence assembly (622 scaffolds, 1.38Gb, N50=5.9Mb) and its annotation will be provided through a Web Genome Browser to the public research community. Our strategy to obtain and finalize the genome assembly as well as results on population diversity will be presented. The genome sequence of O. cumana will enable the characterization of its physiology and development. Avirulence genes should be identified more efficiently and, as putative interactor with sunflower proteins, should help in identifying new resistance genes in sunflower. This resource will help in understanding parasitic plants’ biology and evolution, like parasitism capacity acquisition.

Trabajo presentado en el 14th World Congress on Parasitic Plants (From genome to field), celebrado en Asilomar (California) el 24 y 25 de junio de 2017.

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