Abstract
BackgroundFlavescence dorée is the most serious grapevine yellows disease in Europe. It is caused by phytoplasmas which are transmitted from grapevine to grapevine by the leafhopper Scaphoideus titanus. Differences in susceptibility among grapevine varieties suggest the existence of specific genetic features associated with resistance to the phytoplasma and/or possibly with its vector. In this work, RNA-Seq was used to compare early transcriptional changes occurring during the three-trophic interaction between the phytoplasma, its vector and the grapevine, represented by two different cultivars, one very susceptible to the disease and the other scarcely susceptible.ResultsThe comparative analysis of the constitutive transcriptomic profiles suggests the existence of passive defense strategies against the insect and/or the phytoplasma in the scarcely-susceptible cultivar. Moreover, the attack by the infective vector on the scarcely-susceptible variety prompted immediate and substantial transcriptomic changes that led to the rapid erection of further active defenses. On the other hand, in the most susceptible variety the response was delayed and mainly consisted of the induction of phytoalexin synthesis. Surprisingly, the jasmonic acid- and ethylene-mediated defense reactions, activated by the susceptible cultivar following FD-free insect feeding, were not detected in the presence of the phytoplasma-infected vector.ConclusionsThe comparison of the transcriptomic response in two grapevine varieties with different levels of susceptibility to Flavescence dorèe highlighted both passive and active defense mechanisms against the vector and/or the pathogen in the scarcely-susceptible variety, as well as the capacity of the phytoplasmas to repress the defense reaction against the insect in the susceptible variety.
Highlights
Flavescence dorée is the most serious grapevine yellows disease in Europe
The phytoplasma was found in 16 S. titanus specimens fed on Flavescence dorée (FD)-infected leaves, which corresponds to 28% of the insects collected from Response to the three-trophic grapevine-phytoplasma-insect interaction (FDSt) treatments
All the plantlets used in noSt and HSt treatments and analyzed by real-time PCR proved to be negative for the presence of the FD phytoplasma
Summary
Flavescence dorée is the most serious grapevine yellows disease in Europe It is caused by phytoplasmas which are transmitted from grapevine to grapevine by the leafhopper Scaphoideus titanus. Phytoplasmas are plant pathogenic wall-less grampositive bacteria associated with numerous diseases in wild and cultivated species worldwide [1]. They are phloem-obligate parasites, are very difficult to cultivate in an axenic medium [2] and are characterized by a transmission mediated by specific insect vectors or by grafting. FD, transmitted by the leafhopper Scaphoideus titanus (St) [4], is highly epidemic It is caused by several isolates of phytoplasmas classified in the phylogenetic group 16SrV, subgroups C and D [3]. With a view to create more sustainable agriculture, they should be combined with modern approaches, such as the elicitation of grapevine defenses and/or the selection of resistant plant material
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