Mgaloblishvili Rpv29 and Rpv31 loci reveal new insights on downy mildew resistance sources in Vitis vinifera

Downy mildew, a disease caused by Plasmopara viticola (Berk. et Curt.) Berl. and De Toni, is one of the strongest threats to grapevine (Vitis vinifera L.) production. Recently, sources of resistance to downy mildew were identified among Caucasian germplasm. Among them, the Georgian variety Mgaloblishvili revealed a unique resistance mechanism. A genome wide association study (GWAS) allowed the identification of the genetic bases of Mgaloblishvili resistance, the loci Rpv29, Rpv30 and Rpv31. To dissect the three resistance loci, Mgaloblishvili genome was sequenced using PacBio HiFi reads and assembled. A chromosome-scale diploid genome assembly consisting of ~ 986 Mb and a contig N50 length of 25.8 Mb was obtained. A total of 58,912 protein-coding genes were predicted on the two sets of phased chromosomes. A whole genome comparison with the genome of the susceptible reference accession PN40024 was performed. Mgaloblishvili resistance loci were in-depth analyzed in terms of structure, gene content, gene expression and impact of structural variants (SVs) and SNPs (Single Nucleotide Polymorphisms). Furthermore, using DNA sequencing data of Mgaloblishvili self-cross progeny, resistance haplotypes were identified for Rpv30 and Rpv31. The obtained data highlighted Mgaloblishvili resistant phenotype as a consequence of multiple small SVs and SNPs, that eventually results into differential transcriptional regulation. Altogether, these genetic resources will increase the knowledge about downy mildew-grapevine pathosystem. Moreover, they will be available for breeding programs aiming to develop grapevine resistant varieties.