Regulation of Cell Metabolism and Changes in Berry Shape of Shine Muscat Grapevines Under the Influence of Different Treatments with the Plant Growth Regulators Gibberellin A3 and N-(2-Chloro-4-Pyridyl)-N′-Phenylurea

Plant growth regulators Gibberellin A3 (GA3) and N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU) are widely used in ‘Shine Muscat’ cultivation to regulate berry shape and size. However, the molecular mechanisms underlying their regulation of berry shape remain poorly understood. This study was designed to elucidate the cytological processes and molecular basis through which GA3 and CPPU modulate berry morphology in ‘Shine Muscat’. The results showed that spraying GA3 or CPPU alone increases the hormone levels of endogenous auxin (IAA) and GA3 and reduces the levels of endogenous 6-benzyladenine (6-BA). GA3 treatment resulted in the number of cells per unit area being significantly reduced and the cell transverse and longitudinal diameters being significantly increased. CPPU treatment increases the number of cells per unit area, cell transverse and longitudinal diameters. In the results of CKvsG2 and CKvsC2 transcriptome sequencing, 2793 and 1082 differentially expressed genes (DEGs) were identified, respectively. These DEGs are significantly enriched in Gene Ontology (GO) terms related to plant hormones; the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that the zeatin biosynthesis pathway (ko03030) is significantly enriched. The Arabidopsis response regulator (ARR) is down-regulated in response to GA3 application and up-regulated in response to CPPU application. Transient overexpression of VvARR (OE-VvARR) in ‘Shine Muscat’ berry increased the number of berry cells and cell transverse and longitudinal diameters. Furthermore, virus-induced gene silencing of VvARR (VIGS-VvARR) reduced the number of berry cells but increased cell transverse and longitudinal diameters. The OE-VvARR grape hormone levels of endogenous GA3, 6-BA, and IAA were significantly increased. In VIGS-VvARR grape, the levels of endogenous IAA and 6-BA are significantly increased, but there is no significant difference in endogenous GA3. These findings offer novel insights into the molecular mechanisms by which GA3 and CPPU govern berry development, corroborating the hypothesis that VvARR acts as a pivotal regulator mediating the effects of these plant growth regulators on berry cell morphology and, consequently, berry shape.