Speakers - 2026

Title: WGCNA Uncover Molecular Basis of the Sugar-Acid Balance of Watermelon Fruit

Abstract

The sugar-acid ratio (SAR) is a paramount determinant of flavor quality and consumer preference in watermelon (Citrullus lanatus). Despite its agricultural importance, the genetic and molecular basis governing this complex trait remains largely elusive. In this study, an integrated approach combining sugar acid ratio (SAR) and transcriptomic analyses was employed to dissect the regulatory mechanisms underlying SAR in two contrasting watermelon accessions, ‘X’ and ‘S’. Dynamic changes in total soluble solids (TSS), soluble sugars, organic acids, and SAR were monitored across fruit developmental stages, revealing that Xi consistently exhibited higher TSS, sugar and acid contents, and consequently a superior SAR. Weighted gene co-expression network analysis (WGCNA) identified four key modules that were highly correlated with SAR, soluble sugars, and organic acids. From these modules, seven hub genes were prioritized, among which the pectin lyase-like superfamily protein gene (PLSP) was identified as the master switch of SAR metabolism, while polyadenylate-binding protein-interacting protein 4-like (PBPIP4L) also revealed a positive correlation with SAR. Genomic analysis revealed a 61-bp deletion in the first exon of PLSP in Xi, which was absent in Sa, potentially accounting for its enhanced expression in Xi and the resulting higher SAR. Similarly, allelic variation in the promoter region of PBPIP4L advances the binding of transcription factor GTGANTG10, thereby regulating the gene expression in ‘Xi’ and provoking the increment of SAR. Phylogenetic and multiple sequence alignment analyses demonstrated that PLSP and PBPIP4L are evolutionarily conserved across diverse fruit species, including melon, tomato, and apple. Collectively, these findings elucidate the molecular basis of SAR regulation, identify key candidate genes, and provide valuable resources for molecular breeding aimed at enhancing watermelon flavor.