Summary: In maize (Zea mays L.), leaves are essential for photosynthesis and transpiration and leaf yellowing is regulated by carotenoid metabolism, hormonal signalling and environmental factors. However, the molecular mechanisms linking drought stress and leaf yellowing remain poorly understood. ZmNCED3, a key regulator of carotenoid degradation and drought stress responses, plays a critical role in ABA biosynthesis, but its upstream regulatory mechanisms remain unclear. This study investigates the association between leaf‐yellowing mutations and drought stress response in maize. Through map‐based cloning and allelism tests, we identified ZmCAAX as the causal gene underlying the yp1 mutant phenotype. ZmCAAX encodes a CAAX amino‐terminal protease family protein. Overexpression of ZmCAAX increases drought sensitivity, whereas knockout mutants exhibit enhanced drought resistance. ZmCAAX physically interacts with ZmNCED3 and promotes its degradation. Under drought stress, the expression of ZmCAAX decreases, resulting in increased ZmNCED3 levels, which in turn promotes carotenoid degradation and ABA biosynthesis. Based on these findings, designing ZmCAAX gene knockouts or selecting natural variant alleles of ZmCAAX could significantly enhance drought stress resistance and carotenoid content. This genetic strategy may be applied to maize breeding to improve maize quality and drought stress resistance.

Efficient chloroplast development underpins photosynthetic efficiency, biomass accumulation, and ultimately crop productivity. In this study, we characterized wgsl2-0, a stable white-green striped leaf mutant isolated from an ethyl methanesulfonate-mutagenized RP125 population of maize (Zea mays L.). The mutant maintained clear longitudinal striping throughout development and displayed lower chlorophyll content, reduced levels of several chlorophyll precursors and carotenoids, and reduced net photosynthetic rate in the green mutant sectors measured relative to WT. Cytological and ultrastructural analyses showed that the white sectors contained poorly differentiated chloroplasts with disorganized thylakoid membranes and abnormal leaf cellular architecture. Genetic analysis supported control by a single recessive nuclear locus. Fine mapping delimited the locus to an approximately 3.04 Mb interval on chromosome 1 between InDel-14 and InDel-26 and identified Zm00001eb043060, designated ZmWGSL2, as the most likely candidate gene. An independent nonsense allele, wgsl2-1, failed to complement wgsl2-0, strengthening the genetic evidence. ZmWGSL2 is a chloroplast-localized P-type PPR protein lacking recognizable E, E+, or DYW extensions. Representative Sanger chromatograms revealed altered rpoB nucleotide peak patterns in wgsl2-0, but these qualitative observations do not establish direct regulation of rpoB RNA editing by ZmWGSL2. Sector-specific reductions in several photosynthesis-associated plastid transcripts were observed in the white leaf sectors. Together, these results provide strong genetic evidence for ZmWGSL2 as the most likely candidate gene associated with chloroplast development and leaf-colour formation in maize.