Diversity of carotenoid composition, sequestering structures and gene transcription in mature fruits of four Prunus species

The genus Prunus contains many fruits used in the human diet, which exhibit a variety of different flavors. However, publications on the diversity of carotenoid profiles and sequestering structures in Prunes fruits are limited. In this study, carotenoids and their associated sequestering structures in mature fruits of four Prunus species, including peach [Prunus persica (L.) Batschi], nectarine [Prunus persica (L.) Batschi var. nucipersica], plum (Prunus salicina L.), and apricot (Prunus armeniaca L.) were investigated. HPLC-PAD analysis revealed that mature fruits all accumulated carotenoid esters, while their profiles and levels differed significantly. Transcription analysis suggested a positive correlation between carotenogenic genes and carotenoid profiles. Transmission electron microscopy (TEM) analysis revealed a common globular chromoplast in Prunus. However, the number and size of plastids and plastoglobules varied between species. Noticeably, the while-flesh Ruiguang 19 nectarine contained plastids similar to chromoplasts, except with smaller plastoglobules. In addition, it seemed like a lipid-dissolved beta-carotene form in apricot fruits, which is more effectively absorbed by humans than the solid-crystalline form. Moreover, the lowest transcriptions of plastid-related genes were found in Friar plum, and GLK2 and OR genes were presumed to be associated with the largest chromoplasts observed in apricot. We investigated the correlations among carotenoid accumulation, plastid characteristics and gene transcription and found that chromoplast development is likely more important in determining carotenoid accumulation than carotenogenic transcription in Prunus fruits. This study presents the first report on the diversity of carotenoid sequestering structures in Prunus fruits and suggests some crucial genes associated with diversity.