The WRKY53-BCM/SGR module controls plant senescence via chlorophyll degradation in watermelon

Senescence is a complex biological process coordinately regulated by multiple genes at the molecular level. Deciphering its regulatory mechanisms holds significant potential for enhancing crop yield and stress resistance. However, research on senescence-related genes in watermelon has been limited due to its narrow genetic basis and lack of natural variation. In this study, we identified an early-senescence inbred line, WM103, which displays a pale green phenotype at the seedling stage that transitions to yellow at maturity. Genetic analysis indicated this mutant phenotype was control by a single recessive gene. Combined BSA-seq and linkage analysis in a large F2 population, we identified Cla97C10G186360 as the candidate gene, which encodes a BALANCE OF CHLOROPHYLL METABOLISM (ClBCM) protein. A 90 bp deletion at the junction between 6th exon and intron of ClBCM in WM103 led to a truncated protein. Further functional validation through virus-induced gene silencing (VIGS) and CRISPR/Cas9-mediated knockout confirmed that ClBCM downregulation accelerates senescence. In addition, molecular interaction assays revealed a direct physical interaction between ClBCM and ClSGR. Moreover, ClWRKY53 was found to regulate this network by binding to the ClBCM promoter and suppressing its transcription, thereby promoting chlorophyll degradation and senescence. These findings provide novel insights into the molecular regulation of senescence in watermelon and establish a theoretical framework for genetic improvement of fruit quality and stress tolerance in cucurbit crops.