Identification and functional classification of differentially expressed proteins and insight into regulatory mechanism about flower color variegation in peach

Genetic mechanism underlying peach flower color variegation has been intensively investigated at transcriptome level, but an elucidation at proteome level is still scarce. In this study, we performed proteome analysis with a peach cultivar bearing white and red flowers simultaneously on the same tree, and identified the differentially expressed proteins (DEPs) in the red and white flowers at different development stages. A total of 149 DEPs were identified. Among which, 99 were from peach flower buds, and 50 were from expanded but unflushed flowers. It is noteworthy that about 70% of the DEPs are upregulated in red flowers, and the enriched pathways in red flowers at protein level mainly include starch and sucrose metabolism, carbon fixation, and glycolysis (AMY1, UGP, PGK3, TPI, PPA, ATP5H, and RuBisCO), which provide more substrate and energy for anthocyanin biosynthesis. In addition, a number of RNA-binding proteins (RBPs) and proteasome which play key roles in the regulation of gene expression at levels of transcription, splicing and mRNA stability are also found to upregulate in red flowers. Among them, eight glycine-rich RBPs (spot A26, A34, A54, A71, A72, A74, B24, and B42) and a branch point-bridging protein (spot B4) are identified as important proteins involving in alternative splicing of mRNA. As a result of alternative splicing, anthocyanidin synthase (ANS) activity is found to express dramatically higher in red flowers. Besides, a GST protein (XP_007200490.2) involving in anthocyanin transportation is found to significantly upregulate in red flower buds. Unlike the previous reports based on transcriptome analysis, no proteins coded by structural genes in anthocyanin biosynthesis were found obviously upregulated in red flowers in this study. Our findings indicated that flower color variegation should be regulated at both transcriptional and post-transcriptional levels, and genes involved in transcripts alternative splicing and anthocyanin transportation were essential for flower color variegation in peach.