The transcription factor CsbHLH60 relieves high‐temperature inhibition of chlorophyll degradation in citrus

Rising global temperature threatens fruit quality. As one of the most economically valuable fruits worldwide, citrus suffers from high-temperature-induced chlorophyll retention during ripening, significantly reducing commercial value. Comparative physiological analyses revealed that citrus fruit stored at 30°C exhibited markedly impaired chlorophyll degradation and failed to undergo normal degreening, in stark contrast to those maintained at 20°C. This temperature-dependent suppression of degreening was closely associated with a significant downregulation of key chlorophyll catabolic genes (CCGs). By integrating weighted gene co-expression network analysis (WGCNA) of a stay-green mutant, we identified the transcription factor CsbHLH60, a nuclear-localized transcriptional activator, from a chlorophyll-associated module. CsbHLH60 directly binds E-box motifs in the promoters of CsSGR and CsRCCR to drive their expression, a finding validated by ChIP-qPCR and EMSA assays. Transient overexpression of CsbHLH60 in citrus peel accelerated chlorophyll degradation and, importantly, overcame high-temperature-induced repression to restore degreening, whereas RNAi-mediated silencing at 20°C significantly impeded normal degreening of the peel. Mechanistically, high temperature imposes a dual "double-lock" suppression on CsbHLH60, concurrently repressing its transcription and promoting its protein degradation, thereby depleting functional activator levels. Collectively, our findings establish CsbHLH60 as a pivotal temperature-responsive regulator that directly couples temperature signaling to chlorophyll catabolism and is capable of overriding the high-temperature-induced suppression of chlorophyll degradation, thereby highlighting its potential as a molecular target for mitigating climate-driven declines in citrus fruit appearance quality.