Expression of disease resistance in genetically modified grapevines correlates with the contents of viral sequences in the T-DNA and global genome methylation

Abstract

Increased tolerance to pathogens is an important goal in conventional and biotechnology-assisted grapevine breeding programs worldwide. Fungal and viral pathogens cause direct losses in berry production, but also affect the quality of the final products. Precision breeding strategies allow the introduction of resistance characters in elite cultivars, although the factors determining the plant's overall performance are not fully characterized. Grapevine plants expressing defense proteins, from fungal or plant origins, or of the coat protein gene of grapevine leafroll-associated virus 3 (GLRaV-3) were generated by Agrobacterium-mediated transformation of somatic embryos and shoot apical meristems. The responses of the transformed lines to pathogen challenges were investigated by biochemical, phytopathological and molecular methods. The expression of a Metarhizium anisopliae chitinase gene delayed pathogenesis and disease progression against the necrotrophic pathogen Botrytis cinerea. Modified lines expressing a Solanum nigrum osmotin-like protein also exhibited slower disease progression, but to a smaller extent. Grapevine lines carrying two hairpin-inducing constructs had lower GLRaV-3 titers when challenged by grafting, although disease symptoms and viral multiplication were detected. The levels of global genome methylation were determined for the genetically engineered lines, and correlation analyses demonstrated the association between higher levels of methylated DNA and larger portions of virus-derived sequences. Resistance expression was also negatively correlated with the contents of introduced viral sequences and genome methylation, indicating that the effectiveness of resistance strategies employing sequences of viral origin is subject to epigenetic regulation in grapevine.

Scion Breeding for Resistance to Biotic Stresses

“…Several transgenic cultivars expressing CP or MP were produced including the wine grape cultivars 'Chardonnay' (Mauro et al 1995;Dal Bosco et al 2018), 'Nebbiolo', 'Lumassina' and 'Blaufränkish' (Gambino et al 2005, and the table grape cultivars 'Thompson Seedless' (Scorza et al 1996), 'Superior Seedless' (Martinelli et al 2000) and 'Russalka' (Gölles et al 2000;Maghuly et al 2006). These cultivars were engineered for resistance to Arabis mosaic virus, grapevine fanleaf virus (GFLV), tomato ringspot virus, grapevine leafroll-associated virus 3, grapevine virus A and grapevine virus B (Laimer et al 2009;Saporta et al 2016;Dal Bosco et al 2018). The insertion and expression of CP or MP genes, as well as the level of methylation of transgenes and their regulatory sequence elements, were extensively characterized in transgenic cultivars.…”

Emerging Roles of Epigenetics in Grapevine and Winegrowing

“…Most of the research on this topic suggests that reduced DNA methylation increases the responsiveness of the plant immune system [ 12 ]. Indeed, in grapevine, the resistance conferred to leafroll-associated virus 3 (GLRaV-3) in transgenic plants expressing the coat protein GLRaV-3 was negatively correlated with the overall levels of genome methylation [ 87 ].…”

Comparative transcriptome analyses between cultivated and wild grapes reveal conservation of expressed genes but extensive rewiring of co-expression networks

“…However, a broader characterization of the mechanisms underlying the resistance responses of wild grapes has only recently began to emerge (Marrano et al 2018;Wang et al 2019;Daldoul et al 2020). Genetic diversity and differential regulation of gene expression are largely responsible for the phenotypic plasticity and resistance mechanisms in grapes (Dal Santo et al 2013;Cramer et al 2014;Fennell et al 2015;Ghan et al 2017;Zhou et al 2019), although higher order regulatory processes, such as epigenetic modifications and genome-environment interactions, also have been demonstrated to modulate grapevine responses to the environment (Dal Bosco et al 2018;Magris et al 2019).…”