The BoEMB1923-BoPORBs module regulates chlorophyll biosynthesis in cabbage

Embryo defective 1923 (EMB1923) is important for plant embryo development, but its other functions and associated molecular mechanisms remain unclear. Here, we characterized a yellow-green leaf (ygl) mutant in Brassica oleracea, which has significantly reduced chlorophyll levels and abnormal chloroplasts compared to the wild type. Map-based cloning revealed that a 15-bp deletion in the coding region of BoEMB1923 (Brassica oleracea embryo defective 1923) causes the ygl phenotype. Functional analysis demonstrated that BoEMB1923 positively regulates chlorophyll biosynthesis and localizes in chloroplasts. A yeast two-hybrid assay showed that BoEMB1923 and yBoEMB1923 (mutant-type) interact with BoPORB1 and BoPORB2, and these interactions were further confirmed by BiFC and Co-IP assays. The BoEMB1923 mutation reduced BoPORB enzyme activity by 40% and chlorophyllide a (Chlide a) production by 33% in ygl, ultimately resulting in impaired chlorophyll biosynthesis. Taken together, our results reveal the function of BoEMB1923 in regulating chlorophyll biosynthesis by interacting with BoPORBs, which provides rare insight into the molecular mechanisms underlying leaf color formation in cabbage.