Cytological, Physiological, and Transcriptome Analysis of Leaf-Yellowing Mutant in Camellia chekiangoleosa

Color variation in plant leaves has a significant impact on their photosynthesis and plant growth. Camellia chekiangoleosa yellow-leaf mutants are ideal materials for studying the mechanisms of pigment synthesis and photosynthesis, but their mechanism of leaf variation is not clear. We systematically elucidated the intrinsic causes of leaf yellowing in the new Camellia chekiangoleosa variety 'Diecui Liuji' in terms of changes in its cell structure, pigment content, and transcript levels. This study indicates that the incomplete structure of chloroplast-like vesicles, the decrease in blue-green chlorophyll a, and the increase in yellow-green chlorophyll b in yellowing leaves are the direct causes of yellowing-leaf formation. The high expression of genes that catalyze the degradation of chlorophyll a (PAO and RCCR) and its conversion to chlorophyll b (CAO) in yellowing leaves leads to a decrease in the chlorophyll a content, while the low expression of CLH genes is the main reason for the increase in the chlorophyll b content. We also found transcription factors such as ERF, E2F, WRKY, MYB, TPC, TGA, and NFYC may regulate their expression. RT-qPCR assays of 12 DEGs confirm the RNA-seq results. This study will provide a foundation for investigating the transcriptional and regulatory mechanisms of leaf color changes.