ZmbHLH180 promotes drought-induced chlorophyll degradation by directly activating NON-YELLOW COLORING in maize (Zea mays).

Drought is a major environmental constraint that causes premature leaf senescence and limits crop growth and productivity. Although the phenomenon of drought-induced senescence is well-documented, its underlying physiological and molecular mechanisms remain poorly understood. In this study, we investigated leaf senescence in maize (Zea mays L.) under drought conditions and identified distinct responses between the drought-sensitive inbred line B73 and the drought-tolerant line SHEN137. To uncover the genetic basis of drought-induced senescence, transcriptome analysis was performed using five maize inbred lines with varying drought sensitivities. We identified NON-YELLOW COLORING (NYC), encoding a key enzyme in chlorophyll degradation, which was significantly upregulated in drought-sensitive lines compared to drought-tolerant lines. NYC expression correlates with the transcription factor ZmbHLH180 under drought stress. Overexpression of ZmbHLH180 in both maize and Arabidopsis thaliana accelerates chlorophyll degradation and promotes leaf senescence. Transcriptional activity and DNA-binding assays indicate that ZmbHLH180 directly binds to E-box motifs (CANNTG) in the NYC promoter region and activates its transcription. These findings demonstrate a key regulatory mechanism in which ZmbHLH180 mediates drought-induced chlorophyll degradation and leaf senescence through direct transcriptional activation of NYC, providing novel insights into the genetic regulation of drought responses and potential targets for breeding drought-resilient maize varieties.