QTL mapping for berry firmness and functional characterization of a prioritized candidate gene VvNAC83 in grape

Grape is a globally significant fruit crop of high economic value. Berry firmness is a crucial quality trait that directly influences sensory perception, post-harvest shelf life, transportability, and processing suitability. However, the key regulatory genes and molecular mechanisms underlying grape berry firmness remain poorly characterized. To identify quantitative trait loci (QTLs) for grape berry firmness, an F₁ mapping population was constructed by crossing the low-firmness female parent Muscat Hamburg with the high-firmness male parent Red Globe. A high-density integrated genetic map spanning 2131.69 centimorgans (cM) was constructed using 7872 SNP markers distributed across 19 linkage groups. A total of 28 QTLs were detected across three consecutive years (2019, 2020, 2022). Candidate gene screening via RT-qPCR identified VvNAC83, a nuclear-localized transcription factor gene, as a prioritized candidate gene. Transient overexpression in grape berries resulted in a moderate but statistically significant increase in firmness, and stable overexpression in tomato yielded similar results. In transgenic tomato berries, VvNAC83 overexpression induced distinct anatomical alterations, specifically characterized by a thicker cuticle and increased cell density. This study provides valuable insights into the genetic basis of berry firmness and provides a foundational basis for further molecular studies.