Occurrence of White Flesh Color and Refreshing Flavor Following Phytoene Synthase 2A Gene Variation in Loquat Fruit

Loquat fruits from the apple tribe of Rosaceae ripen from late spring to early summer, when most fresh fruits are out of season. Compared with the orange-fleshed varieties, the white-fleshed varieties are usually preferentially chosen by consumers for a more favorable flavor. Though the breeding of white-fleshed cultivars with large fruit size greatly promoted the development of loquat production, the mechanisms of how fruits with lighter pigments are generated and how fruit flavor changes following flesh color shifting remain to be elucidated. Pigment measurements indicated carotenoids as the dominant pigment underlying the change in flesh color changing. Genotyping and haplotyping of 807 loquat accessions revealed that the rise of PSY2Ad-PSY2Ad genotype blocks carotenoids accumulation and confers to white flesh color of loquat fruit. Analysis of widely targeted metabolomes on 18 representative cultivars identified 1420 metabolites, with 223 differentially accumulated metabolites between the two groups. Further metabolite comparison demonstrated that low levels of bitter or astringent compounds, such as flavonoids, lignans and coumarins, phenolic acids, nucleotides, alkaloids, and terpenoids, may confer to a refreshing flavor of white-fleshed fruits. Furthermore, 18 metabolic biomarkers were identified by machine learning to distinguish fruits with diverse flesh colors. This work gives insights into the understanding of how fruit color variation associated with flavor and also promotes white-fleshed loquat breeding by genus-wide genotyping.蔷薇科苹果族的枇杷果实，成熟期为晚春至初夏，此时多数鲜食鲜果已过上市旺季。与橙肉品种相比，白肉品种通常因风味更佳而更受消费者青睐。尽管培育大果型白肉品种极大推动了枇杷产业发展，但果肉色素变浅的成因以及果肉色泽转变伴随的风味调控机制，仍有待阐明。色素检测结果显示，类胡萝卜素（carotenoids）是调控果肉色泽变化的核心色素。对807份枇杷种质资源进行基因分型与单倍型分析后发现，PSY2Ad-PSY2Ad基因型的出现会阻断类胡萝卜素积累，进而赋予枇杷果实白肉性状。对18个代表性品种开展广泛靶向代谢组（widely targeted metabolomes）分析，共鉴定出1420种代谢物，两组间存在223种差异积累代谢物。进一步的代谢物比较分析表明，白肉果实中苦味或涩味物质（如黄酮类、木脂素、香豆素、酚酸、核苷酸、生物碱及萜类）含量较低，这可能是其风味清爽的原因。此外，通过机器学习（machine learning）鉴定出18种代谢生物标志物，可用于区分不同果肉色泽的枇杷果实。本研究不仅深化了对果实色泽变异与风味关联机制的认知，还通过全属基因分型技术推动了白肉枇杷的育种工作。