Globular and crystalloid chromoplasts were observed to be region specifically formed in sweet orange (Citrus sinensis) flesh and converted from amyloplasts during fruit maturation,which was associated with the composition of specific carotenoids and the expression of carotenogenic genes.Results of high-performance liquid chromatography (HPLC) analysis of carotenoids indicated that the accumulation of excessive lycopene or β-carotene probably promotes the formation of crystalloid chromoplasts,while the accumulation of lutein and β-violaxanthin was associated with the formation of globular chromoplasts.Unlike plastid differentiation in citrus flavedo,the chromoplast differentiation provides a new patternfor further research.Subsequently,we identified about 1400 proteins that were predicted to be chromoplast-localized,which is the comprehensive proteomic data up to now.Based on the predicted functions of these identified plastid proteins,a large proportion (~60%) of the chromoplast proteome of sweet orange are constituted by proteins involved in carbohydrate metabolism,amino acid/protein synthesis,and secondary metabolism.Of note,HDS (hydroxymethylbutenyl 4-diphosphate synthase),PAP (Plastid-lipid-associated protein) and psHSPs (plastid small heat shock proteins) involved in the synthesis or storage of carotenoid and stress response are among the most abundant proteins identified.Comparative proteomics analysis found that numbers of proteins to be associated with chromoplasts differentiation and senescence e.g.marked decrease in abundance of the proteins participating in the translation machinery through ribosome assembly;increase in abundance of the proteins involved in terpenoid biosynthesis,stress responses,and development.Interestingly,a strong increase in abundance of several plastoglobule-localized proteins coincided with the formation of plastoglobules in the chromoplast.The proteomic data also showed that stable functioning of protein import,suppression of ribosome assembly,and accumulation of chromoplast proteases are correlated with the amyloplast-to-chromoplast transition;thus,these processes may play a collective role in chromoplast biogenesis and differentiation.In conclusion,this comprehensive proteomic study identified many potentially new plastid-localized proteins and provides insights into the potential developmental and molecular mechanisms underlying chromoplast biogenesis,differentiation,and senescence in sweet orange flesh.