Loquat can be divided into two groups of red- and white- fleshed loquat cultivars according to the flesh color, indicating different carotenoid accumulation patterns among the two cultivars. Meanwhile, the carotenoid accumulation patterns are also different among tissues of flesh, peel and leaf. Recently, a study carried out in Institute of Fruit Science revealed the roles of phytoene synthase (PSY) gene family members on tissue- and cultivar-specific accumulation of carotenoids in loquat. This research has been published in the Journal of Experimental Botany (2014, DOI: 10.1093/jxb/eru257), entitled “Involvement of multiple phytoene synthase genes in tissue and cultivar-specific accumulation of carotenoids in loquat”. Ph.D student Xiumin Fu is the first author of this paper and Professor Changjie Xu is the corresponding author. This research was supported by the National Natural Science Foundation in China.
Using RNA-Seq technology, gene sequence analysis, gene expression level analysis and functional analysis, it was concluded that EjPSY1, EjPSY2A and EjPSY2B were responsible for carotenoid accumulation loquat peel, fruit and green tissue, respectively. EjPSY3 might be the ancestor of other EjPSY gene members although had no function. A mutant EjPSY2Ad with the same tissue specificity and expression level as EjPSY2A, but lacking the C-terminal region and corresponding catalytic activity, was discovered in white-fleshed varieties, explaining the lack of carotenoids in the white flesh. EjPSY1 and EjPSY2B explained well how peel and leaf tissues can still accumulate carotenoids in white-fleshed cultivars, which have lost the functional EjPSY2A.
Besides, loquat is the first plant reported to possess four members in PSY gene family, although this is also true to another Rosaceae plant, apple, according to genome sequences. Therefore, this study can provide a reference for similar studies in other plants on evolution and function analysis of PSYs as well as on the relationship between PSYs and carotenoid accumulation.
