Functional analysis of CsCAB1 in regulating leaf color variation in tea plants (Camellia sinensis)

Albino leaf is a valuable agronomic trait in tea plants, characterized by its distinctive color and associated superior quality and health benefits. In this study, an albino mutant 'Fu'an Dabaicha' with both green and etiolated branches was identified and subjected to full-length transcriptome analysis. The gene family members of chlorophyll a/b binding (CAB) were found to be significantly differentially expressed in yellow and green leaves. Functional complementation in Arabidopsis revealed that CsCAB1 could rescue the etiolated phenotype of cab mutant. The overexpression lines showed increased chlorophyll a content and up-regulated expression levels of genes involved in chlorophyll biosynthesis. Yeast two-hybrid (Y2H) screening and validation revealed that CsCAB1 interacts with thylakoid-related proteins, including thylakoid formation 1 (CsTHF1) and oxygen-evolving enhancer protein of photosystem II (CsPsbP1). Further bimolecular fluorescence complementation (BiFC) assays confirmed that these interactions occur on chloroplasts, suggesting a role in modulating the assembly and stability of photosystem Ⅱ (PSⅡ) complex. These findings indicate that CsCAB1 regulates tea leaf albino variation through a coordinated mechanism affecting both chlorophyll a metabolism and photosystem complex integrity.