Dissecting the dual role of light regarding the plasticity of grape physiology and gene regulation through daylength simulation in a semi-arid region

Abstract

Context and purpose of the study. Daylength is a key climatic factor within the terroir concept. However, the complex interplay of multiple variables in regions with varying daylengths makes it challenging to isolate and investigate this specific factor. To address this, a three-year experiment (2021-2023) was conducted in a semi-arid region of China with the longest natural daylength (CK).

Material and methods. To simulate the daylengths of central (20% reduction, MD) and eastern (30% reduction, SD) regions, daily artificial shading was applied to entire grapevines from anthesis to harvest. Microclimatic conditions at the grapevine scale, gas exchange parameters, targeted grape metabolites, and RNA-seq data were collected and analyzed to investigate the physiological and metabolic responses of the grapevines.

Results. The results revealed that shading reduced incident light by 80%, leading to a decline in net assimilation rate, stomatal conductance, and transpiration rate. Phenological stages were delayed, and the main shoot leaf area increased in MD and SD treatments, as evidenced by slower accumulation of total soluble solids and delayed degradation of total acidity. However, these differences in phenological stages and physicochemical parameters diminished before harvest. Compared with CK, MD and SD grapes exhibited delayed anthocyanin accumulation, significantly lower flavonol levels, and higher concentrations of C6/C9 compounds, terpenes, and norisoprenoids. Notably, compensation effects were observed, as the significant differences in metabolites disappeared by harvest. RNA-seq was performed on grape berries sampled at four time points during the day during three key phenological periods. The differential expressed genes were more abundant at veraison and pre harvest, especially half an hour after shading and half an hour after net removing. The regulated pathways included carbon metabolism, amino acids, starch and sucrose metabolism, and phenylpropanoid biosynthesis. The WGCNA and network analysis revealed the key genes and transcription factors (TF) responsible for the daylength changes including VviWRKY3, VviNF-YB3, and VviNF-YC9. The binding sites of these candidate TFs were identified through DNA affinity purification sequencing, and the Dual-luciferase reporter assay was applied to investigate the transactivation of these TFs.