Current understanding of grapevine defense mechanisms against the biotrophic fungus (Erysiphe necator), the causal agent of powdery mildew disease

The most economically important disease of cultivated grapevines worldwide is powdery mildew(PM)caused by the ascomycete fungus Erysiphe necator.The majority of grapevine cultivars used for wine,table grape,and dried fruit production are derived from the Eurasian grape species Vitis vinifera because of its superior aroma and flavor characteristics.However,this species has little genetic resistance against E.necator meaning that grape production is highly dependent on the frequent use of fungicides.The integration of effective genetic resistance into cultivated grapevines would lead to significant financial and environmental benefits and represents a major challenge for viticultural industries and researchers worldwide.This review will outline the strategies being used to increase our understanding of the molecular basis of V.vinifera susceptibility to this fungal pathogen.It will summarize our current knowledge of different resistance loci/genes that have evolved in wild grapevine species to restrict PM infection and assess the potential application of these defense genes in the generation of PM-resistant grapevine germplasm.Finally,it addresses future research priorities which will be important in the rapid identification,evaluation,and deployment of new PM resistance genes which are capable of conferring effective and durable resistance in the vineyard.

Transcriptional profiling reveals multiple defense responses in downy mildew-resistant transgenic grapevine expressing a TIR-NBS-LRR gene located at the MrRUN1/MrRPV1 locus

Grapevine downy mildew(DM)is a destructive oomycete disease of viticulture worldwide.MrRPV1 is a typical TIR-NBS-LRR type DM disease resistance gene cloned from the wild North American grapevine species Muscadinia rotundifolia.However,the molecular basis of resistance mediated by MrRPV1 remains poorly understood.Downy mildew-susceptible Vitis vinifera cv.Shiraz was transformed with a genomic fragment containing MrRPV1 to produce DM-resistant transgenic Shiraz lines.Comparative transcriptome analysis was used to compare the transcriptome profiles of the resistant and susceptible genotypes after DM infection.Transcriptome modulation during the response to P.viticola infection was more rapid,and more genes were induced in MrRPV1-transgenic Shiraz than in wild-type plants.In DM-infected MrRPV1-transgenic plants,activation of genes associated with Ca^(2+)release and ROS production was the earliest transcriptional response.Functional analysis of differentially expressed genes revealed that key genes related to multiple phytohormone signaling pathways and secondary metabolism were highly induced during infection.Coexpression network and motif enrichment analysis showed that WRKY and MYB transcription factors strongly coexpress with stilbene synthase(VvSTS)genes during defense against P.viticola in MrRPV1-transgenic plants.Taken together,these findings indicate that multiple pathways play important roles in MrRPV1-mediated resistance to downy mildew.