Functional Genomics applied to the study of resistance against Powdery Mildew in grapevine

Abstract

Grapevine (Vitis vinifera L.) is one of the most valuable non-climacteric fruit crops worldwide and is susceptible to several pathogens. Powdery Mildew (PM) is one of the most widespread diseases and is caused by the biotrophic fungus Erysiphe necator. This pathogen relies on the host metabolism to complete its life cycle. PM can affect all green tissues, such as leaves and green berries, frequently resulting in a negative effect on grape production. Despite the several studies performed so far, the mechanisms behind grapevine defense are very complex, and responses against PM remain unclear in infected fruits. In order to study the mechanisms involved in grape berries response to PM infection in the early stages of ripening, naturally infected and control grapes from ‘Carignan’ variety were collected at green (EL33) and véraison (EL35) stages and metabolic, transcriptomic and hormonal changes upon PM infection were analyzed. Results demonstrated that PM-susceptible grape berries were able to induce defense mechanisms and accumulate defense-associated metabolites, such as resveratrol, catechins, gallic acid, and long-chain saturated fatty acids, which could be explored as markers of infection at earlier ripening stages on field conditions. Induction of defenses was also previously observed in leaves, but certain responses seem to be organ-specific, such as the reprogramming of fatty acid metabolism and isoprenoid biosynthesis. This study was the first to quantify jasmonates’ levels in PM infected berries suggesting an involvement of specific jasmonates in response to PM. These growth regulators are classically associated with response to necrotrophic fungi. Some LATERAL ORGAN BOUNDARIES (LOB) domain (LBD) and GRAS genes were responsive to powdery mildew and/ or modulated at véraison stage. LBD constitute a family of plant-specific transcription factors with important roles in several plant processes. In this work, a genome-wide analysis was performed to identify and map the LBD genes in the grapevine genome. Fifty LBD genes were identified and grouped in two classes. Expression profiling suggests the involvement of LBD transcription factors in grapevine development, berry ripening and stress responses. GRAS transcription factor family has also been reported as involved in multiple processes; however, their role in fruit ripening is poorly studied. Tomato SlGRAS10 and its grapevine ortholog VviPAT6 were previously suggested as putative regulators of fruit ripening in both climacteric and non-climacteric plants. In this work, preliminary studies and targeted mutagenesis using CRISPR-Cas9 technology were developed in order to study the role of SlGRAS10 in fruit ripening.