CitNAC71-CitNAC76 coordinate cellulose and hemicellulose biosynthesis to regulate high-temperature-mediated granulation in citrus

Abstract Juice sac granulation, a globally pervasive physiological disorder in citrus (Citrus spp.), leads to substantial economic losses annually. The disorder is characterized by the marked accumulation of cell wall components, yet the molecular mechanisms coordinating this process remain poorly understood. Here, we found that high temperature acts as a strong inducer of citrus granulation, triggering a rapid and pronounced accumulation of cellulose and hemicellulose in juice sacs—an early hallmark of the disorder. Through integrated transcriptomic, biochemical, and genetic analyses, we identified Cellulose synthase A 7/8 (CitCesA7/8) and IRREGULAR XYLEM 9/9H/14H (CitIRX9/9H/14H) as essential biosynthetic genes underlying this process. We further revealed that the NAM/ATAF/CUC (NAC) transcription factor CitNAC76 directly responds to high temperature and activates CitCesA7/8 and CitIRX9/9H/14H, acting as a central regulatory hub of cellulose and hemicellulose accumulation during granulation process. Notably, we uncovered a molecular ‘brake’, CitNAC71, which suppresses CitNAC76 expression and compromises its transactivation of CitCesA7/8 and CitIRX9/9H/14H, forming a dual-layered feedback module that fine-tunes cellulose and hemicellulose biosynthesis under heat stress. Together, our study unveiled the CitNAC71-CitNAC76 regulatory circuit that orchestrates stress-induced cell wall remodeling in citrus fruit, providing potential genetic targets for mitigating juice sac granulation and improving postharvest performance in a warming climate.