Abstract
The Eurasian grapevine (Vitis vinifera), a species cultivated worldwide for high-quality wine production, is extremely susceptible to the agent of downy mildew, Plasmopara viticola. Nevertheless, germplasm from Georgia (Southern Caucasus, the first grapevine domestication centre), characterized by a high genetic variability, showed resistance traits to P. viticola. The cultivar Mgaloblishvili exhibited the most promising phenotype in terms of resistance against P. viticola. Its defence response results in: i) low disease intensity; ii) low sporulation; iii) damaged mycelium; iv) production of antimicrobial compounds such as volatile organic compounds (VOCs), whose effectiveness on the pathogen was evaluated by leafdisc assays. At the transcriptomic level, its resistance mechanism is determined by the differential expression of both resistance and susceptible genes. The resistance genes are related to: i) pathogen recognition through PAMP, DAMP and effector receptors; ii) ethylene signalling pathway; iii) synthesis of antimicrobial compounds (VOCs) and fungal wall degrading enzymes; iv) development of structural barriers (cell wall reinforcement). The first putative susceptible gene was the transcription factor VviLBDIf7 gene, whose validation was carried out by dsRNA (double-stranded RNA) assay. In this work, these unique results on plant-pathogen interaction are reviewed with the aim of developing new strategies to control the disease.
Highlights
Archaeological and palaeobotanical findings pointed out the Caucasus as the first grapevine (Vitis vinifera) domestication centre [1]
Transcriptional analysis revealed an overexpression of genes related to the biosynthesis of Volatile organic compounds (VOCs), such as valencene synthase and several cytochrome P450s, in Mgaloblishvili leaves inoculated with P. viticola [16]
Solid-phase microextraction gas chromatography-mass spectrometry analysis and the expression of terpene synthases ((E)-β-caryophyllene synthase, (E)-α-bergamotene synthase, (E, E)-αfarnesene synthase, (E)-β-ocimene synthase, α-terpineol synthase and valencene synthase), revealed the biosynthesis of VOC in Mgaloblishvili leaves inoculated with P. viticola
Summary
Volatile organic compounds (VOCs), such as terpenes, norisoprenoids, alcohols and aldehydes, are frequently emitted by plants in response to attack by pathogens [18]. A candidate S gene for P. viticola resistance has been suggested This gene, named VviLBDIf7, was found to be overexpressed in the susceptible cultivar Pinot noir 24 hours after the inoculation with P. viticola, while its expression was found to be decreased in the resistant Mgaloblishvili cultivar [17]. RNA interference (RNAi) by exogenous doublestranded RNA (dsRNA) is a transient way to knockdown target genes [30] This strategy has been used to knockdown the VviLBDIf7 gene in a highly susceptible grapevine cultivar (Pinot noir) to control P. viticola infections. Clear alterations to both vegetative (hyphae and haustoria) and reproductive structures (sporangiophores) have been identified on leaves treated with dsRNA, resulting in a stunted growth and reduced sporulation [31] These observations prove that VviLBDIf7 gene is a candidate gene to be silenced to reduce susceptibility to P. viticola
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