CauYL, encoding a magnesium chelatase H subunit, is required for chlorophyll accumulation and normal leaf coloration in cauliflower

Fine mapping and CRISPR/Cas9 validation identified CauYL(BOB03G201420), encoding the H subunit of magnesium chelatase, as the causal gene for the yellow-green leaf phenotype in cauliflower. As the primary photosynthetic pigment in plants, chlorophyll captures light energy to drive photosynthesis and regulate plant growth. In addition, it confers green coloration to plants by absorbing blue and red light wavelengths. Despite the important role of chlorophyll in vegetables, the genetic regulation of chlorophyll accumulation in cauliflower remains largely unknown. In this study, we identified a cauliflower mutant "K-6" from an ethyl methanesulfonate (EMS) mutagenized population, that displayed a stable yellow-green phenotype. The mutant showed much lower chlorophyll contents and decreased photosynthetic rate compared with the WT plants. Genetic inheritance analysis revealed that this yellow-green trait was controlled by a recessive gene. The target gene, designated CauYL, was mapped to an approximately 103.07 kb region on chromosome 3, based on BSA-seq and traditional linkage analyses. We identified a candidate gene BOB03G201420 encoding the H subunit of magnesium chelatase. Sequence analysis revealed a non-synonymous single nucleotide polymorphism (SNP) within the coding sequence, resulting in an alanine-to-threonine substitution at a highly conserved residue. We employed CRISPR/Cas9 to knockout the CauYL gene in the WT background, and successfully generated CauYL mutants, which showed a yellow-green trait resembling that of the K-6 mutant. Transcriptome analysis showed that differentially expressed genes between K-6 and WT were significantly enriched in photosynthesis, riboflavin metabolism, and related pathways. Collectively, our results demonstrate that the CauYL gene is essential for maintaining the green coloration and photosynthetic competence of cauliflower, providing a valuable genetic target for improving photosynthetic efficiency and leaf color traits in cauliflower breeding.