Characterization of Carotenoid Accumulation and Carotenogenic Gene Expression During Fruit Development in Yellow and White Loquat Fruit

Accumulation of carotenoids in peel and pulp of the yellow-fleshed loquat ‘Zaozhong 6’ (ZZ6) and the white-fleshed loquat ‘Baiyu’ (BY) were tracked during different fruit development stages, and the expression of 15 carotenogenic genes were analyzed. During loquat fruit ripening the fresh weight content of β-carotene in peel and pulp of ZZ6 increased gradually and peaked at the fully ripe stage, reaching 68.53 µg⋅g−1 FW in the peel and 11.92 µg⋅g−1 FW in the pulp. In BY, the content of β-carotene in the peel increased and peaked at the fully ripe stage, reaching 38.89 µg⋅g−1 FW, while it decreased in the pulp from the original 0.47 µg⋅g−1 FW and reduced to 0.29 µg⋅g−1 FW. The content of β-cryptoxanthin in the peel and pulp of ZZ6 and BY both increased steadily, and peaked at the fully ripe stage; however, the content of lutein decreased in the peel of ZZ6 and increased in the pulp, but in BY, it dropped and then rose in the peel. There was no significant change of β-cryptoxanthin in the pulp of BY. After the breaker stage, the mRNA levels of phytoene synthase (PSY) and chromoplast-specific lycopene β-cyclase (CYCB) were higher in the peel, while CYCB and β-carotene hydroxylase (BCH) mRNAs were higher in the flesh of ZZ6, compared with BY. The results showed that the expression level of PSY, CYCB, and BCH appeared to cooperatively regulate the accumulation of carotenoids.