Abstract
AbstractMultiple grape powdery mildew (PM) genetic resistance (R) loci have been found in wild grape species. Little is known about the defense responses associated with eachRlocus. In this study, we compare the defense mechanisms associated with PM resistance in interspecific crosses segregating for a singleRlocus fromMuscadinia rotundifolia(Run1, Run1.2b, Run2.1, Run2.2),Vitis cinerea(Ren2),V. romanetii(Ren4DandRen4U), and the interspecific hybrid Villard blanc (Ren3). By combining optical microscopy, visual scoring, and biomass estimation, we show that the eightRloci confer resistance by limiting infection at different stages. We assessed the defense mechanisms triggered in response to PM at 1 and 5 days post inoculation (dpi) via RNA sequencing. To account for the genetic differences between species, we developed for each accession a diploid synthetic reference transcriptome by incorporating into thePN40024reference homozygous and heterozygous sequence variants andde novoassembled transcripts. Most of theRloci exhibited a higher number of differentially expressed genes (DEGs) associated with PM resistance at 1 dpi compared to 5 dpi, suggesting that PM resistance is mostly associated with an early transcriptional reprogramming. Comparison of the PM resistance-associated DEGs showed a limited overlap between pairs ofRloci, and nearly half of the DEGs were specific to a singleRlocus. The largest overlap of PM resistance-associated DEGs was found betweenRen3+,Ren4D+, andRen4U+genotypes at 1 dpi, and betweenRen4U+andRun1+accessions at 5 dpi. TheRen3+,Ren4D+, andRen4U+were also found to have the highest number ofRlocus-specific DEGs in response to PM. Both shared andRlocus-specific DEGs included genes from different defense-related categories, indicating that the presence ofE. necatortriggered distinct transcriptional responses in the eightRloci.
Publisher
Cold Spring Harbor Laboratory