Grapevine comparative early transcriptomic profiling suggests that Flavescence dorée phytoplasma represses plant responses induced by vector feeding in susceptible varieties

Abstract

Background 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 . 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. Results The 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. Conclusions The 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. Electronic supplementary material The online version of this article (10.1186/s12864-019-5908-6) contains supplementary material, which is available to authorized users.

Pre-symptomatic modified phytohormone profile is associated with lower phytoplasma titres in an Arabidopsis seor1ko line

“…The fact that the phytohormone levels are identical in H-Ev and no-Ev plants strongly supports the conclusion that the phytohormone modulation in CY-Ev plants is solely due to phytoplasma infection. This is in agreement with the observation that 6 days after Scaphoideus titanus infestation in grapevine, the expression level of genes involved in JA and ABA pathways were similar to those found in non-infested control leaves, while they had been upregulated 3 days after infestation 46 .…”

“…Jasmonates, but not salicylic acid seem to be involved in the response of Atseor1ko line to phytoplasma infection. There are several indications for phytohormone involvement in diverse phytoplasma-plant interactions 4 , but few studies have addressed plant responses at the early stage of infection 40,46 .…”

Flavescence Dorée-Derived Leaf Yellowing in Grapevine (Vitis vinifera L.) Is Associated to a General Repression of Isoprenoid Biosynthetic Pathways

“…Indeed, in Arabidopsis, among the five NCED genes involved in ABA biosynthesis, only AtNCED3 was highly induced by dehydration (Iuchi et al, 2001;Tan et al, 2003;Reviewed by Nambara and Marion-Poll, 2005). This thesis could be supported by the evidence that an up regulation of one NCED member has been detected by a transcriptomic approach on two Italian grapevine varieties (Chardonnay and T. friulano), although in this case no metabolite analyses on ABA have been carried out (Bertazzon et al, 2019).…”

“…Another hypothesis is that the ABA accumulation, as consequence of the FD infection that could mimic the senescence status, could be achieved by the existence of control mechanisms acting on transcript levels of downstream genes with respect to NCED (as already described by Bertazzon et al, 2019), or at post-transcriptional rather than at RNA level; this latter hypothesis would be supported by previous studies which have shown the existence of post-transcriptional regulation especially at ABA signaling gene level (Yang et al, 2017). GGPP could also be channeled to the ubiquinone and other quinone biosynthesis by the action of different key enzymes depicted in Figure 5, but results showed that the expression of VvVTE1, VvVTE3 and VvVTE4 was not repressed in response to FD-infection, although different end products were reduced; they included plastoquinone and ubiquinone-9/-10, which act as carriers of electrons in the chloroplast thylakoids and mitochondrial inner membranes, respectively (Yoshida et al, 2010).…”

“…'Barbera', proteins involved in the dark and light-dependent reactions of PS II were also less abundant (Margaria et al, 2013). Recent Next Generation Sequencing (NGS) analysis of in vitro micro propagated-infected Chardonnay plantlets showed that several genes involved in photosynthesis-related processes of both light and dark phases were down regulated (Bertazzon et al, 2019).…”