Proteomics study of the effects of high pigment-1 on plastid differentiation during the ripening of tomato fruits

The chloroplast-to-chromoplast difference is a highly regulated process. Tomato (Solanum lycopersicum) high-pigment mutant hp-1 shows an enhanced accumulation of carotenoids coupled with an increase in the volume and number of plastids. However, how chromoplasts of hp-1 acquire their specific metabolic characteristics is still unclear. A comparison of proteome profiles from plastids at the mature green, breaker, and red stages of tomato fruits showed 45 differentially expressed proteins. These identified proteins fell into six different functional categories. Our results showed that most of the proteins related to the Calvin cycle increased transitorily only at the early breaker stage, and remained unchanged at the early red stage. We found 18 proteins that were differentially expressed between the wild type and hp-1. The abundance of GCPE in chromoplasts of hp-1 was higher than that in the wild type. Meanwhile, we found that heat shock proteins were only present specifically in the mature green stage chromoplasts of hp-1 but not in the wild type. This suggested that GCPE and heat shock proteins might play important roles in the accumulation of high carotenoids in hp-1. Overall, our results could be helpful for understanding chloroplast-to-chromoplast differentiation and the function of hp-1.