SWATH-MS based proteomics reveals the role of photosynthesis related proteins and secondary metabolic pathways in the colored leaves of sweet olive (Osmanthus fragrans).

Colored leaves, a notable horticultural trait, have high research and ornamental value. The evergreen sweet olive (Osmanthus fragrans), one of the top ten traditional flowers in China, has been cultivated for more than two thousand years. However, in recent years, an increasing number of O. fragrans cultivars with colored leaves have been cultivated for their ornamental value. To study the molecular mechanism underlying the observed changes in leaf color, we selected O. fragrans 'Yinbi Shuanghui' (Y), which has yellow-white leaves, and O. fragrans 'Sijigui' (S), which has green leaves, as materials. Pigment content measurement showed that the chlorophyll, carotenoid and anthocyanin contents in Y were lower than in S. According to the SWATH-MS sequencing results, a total of 3,959 proteins were quantitatively identified, 1,300 of which were differentially expressed proteins (DEPs), including 782 up-regulated and 518 down-regulated proteins in Y compared to S. Functional enrichment analysis of DEPs revealed that down-regulated expression of photosynthesis related proteins may lead to the inhibition of chlorophyll synthesis in Y, this may be the main cause of leaf color change. Moreover, a protein interaction prediction model also showed that proteins such as PetC, PsbO, PsbP, and PsbQ were key proteins in the interaction network, and the up-regulated proteins participating in the anthocyanin and carotenoid pathways may be related to the formation of yellow-white leaves. Taken together, our findings represent the first SWATH-MS-based proteomic report on colored leaf O. fragrans and reveal that chlorophyll synthesis and secondary metabolism pathways contribute to the changes in leaf color.