Identifying Candidate Genes for Grape (<i>Vitis vinifera</i> L.) Fruit Firmness through Genome-Wide Association Studies

The firmness of grape berries is a critical factor influencing their commercial feasibility and is highly valued by both breeders and consumers. However, grape berry firmness is a complex quantitative trait governed by multiple genes, and our understanding of its genetic regulatory network remains incomplete. To elucidate the genetic mechanisms underlying grape berry firmness, this study employed genome-wide association studies (GWAS) to identify potential candidate genes associated with fruit firmness and cellulose content and to explore the gene regulatory network that controls their variation. The comprehensive GWAS results identified <i>CesA</i> as a candidate gene potentially regulating fruit firmness through its involvement in cellulose biosynthesis. To validate these findings, whole-genome gene family identification analysis was conducted. Furthermore, the key gene <i>VvCslD5</i> was selected for functional validation, which included overexpression studies and subcellular localization. This study provides valuable insights into the regulation of biosynthesis and transcriptional signaling pathways that govern the structure of grape cell walls as well as the mechanisms underlying variations in grape firmness. These findings establish a solid foundation for future functional analyses of grape traits and will enhance breeding practices aimed at improving grape quality.