Liu Hongru, Cao Xiangmei, Azam Muhammad, Wang Chunfang, Liu Chenxia, Qiao Yongjin, Zhang Bo
Crop Breeding & Cultivation Research Institute, Shanghai Academy of Agricultural Sciences, Shanghai, China.
Research Center for Agricultural Products Preservation and Processing, Shanghai Academy of Agricultural Sciences, Shanghai, China.
Front Plant Sci. 2022 May 13;13:814677. doi: 10.3389/fpls.2022.814677. eCollection 2022.
Carotenoids are essential pigments widely distributed in tissues and organs of higher plants, contributing to color, photosynthesis, photoprotection, nutrition, and flavor in plants. White- or yellow-fleshed colors in peach were determined by expression of carotenoids cleavage dioxygenase () genes, catalyzing the degradation of carotenoids. The cracked volatile apocarotenoids are the main contributors to peach aroma and flavor with low sensory threshold concentration. However, the detailed regulatory roles of carotenoids metabolism genes remained unclear under UV-B irradiation. In our study, metabolic balance between carotenoids and apocarotenoids was regulated by the expression of phytoene synthase (), β-cyclase (), εcyclase (), and under UV-B irradiation. The transcript levels of , , , and were elevated 2- to 10-fold compared with control, corresponding to a nearly 30% increase of carotenoids content after 6 h UV-B irradiation. Interestingly, the total carotenoids content decreased by nearly 60% after 48 h of storage, while UV-B delayed the decline of lutein and β-carotene. The transcript level of increased 17.83-fold compared to control, partially slowing the decline rate of lutein under UV-B irradiation. In addition, the transcript level of decreased to 30% of control after 48 h UV-B irradiation, in accordance with the dramatic reduction of apocarotenoid volatiles and the delayed decrease of β-carotene. Besides, β-ionone content was elevated by ethylene treatment, and accumulation dramatically accelerated at full ripeness. Taken together, UV-B radiation mediated the metabolic balance of carotenoid biosynthesis and catabolism by controlling the transcript levels of , , , and in peach, and the transcript level of showed a positive relationship with the accumulation of β-ionone during the ripening process. However, the detailed catalytic activity of PpCCD4 with various carotenoid substrates needs to be studied further, and the key transcript factors involved in the regulation of metabolism between carotenoids and apocarotenoids need to be clarified.
类胡萝卜素是广泛分布于高等植物组织和器官中的必需色素，对植物的颜色、光合作用、光保护、营养和风味都有贡献。桃果肉的白色或黄色由类胡萝卜素裂解双加氧酶（）基因的表达决定，该基因催化类胡萝卜素的降解。裂解产生的挥发性脱辅基类胡萝卜素是桃香气和风味的主要贡献者，其感官阈值浓度较低。然而，在UV-B辐射下，类胡萝卜素代谢基因的详细调控作用仍不清楚。在我们的研究中，在UV-B辐射下，八氢番茄红素合酶（）、β-环化酶（）、ε-环化酶（）和的表达调节了类胡萝卜素和脱辅基类胡萝卜素之间的代谢平衡。与对照相比，、、和的转录水平提高了2至10倍，对应于UV-B辐射6小时后类胡萝卜素含量增加近30%。有趣的是，储存48小时后，总类胡萝卜素含量下降了近60%，而UV-B延缓了叶黄素和β-胡萝卜素的下降。与对照相比，的转录水平增加了17.83倍，部分减缓了UV-B辐射下叶黄素的下降速率。此外，UV-B辐射48小时后，的转录水平降至对照的30%，这与脱辅基类胡萝卜素挥发物的显著减少和β-胡萝卜素的延迟减少一致。此外，乙烯处理提高了β-紫罗兰酮的含量，在完全成熟时积累显著加速。综上所述，UV-B辐射通过控制桃中、、、和的转录水平介导了类胡萝卜素生物合成和分解代谢的代谢平衡，并且在成熟过程中，的转录水平与β-紫罗兰酮的积累呈正相关。然而，PpCCD4对各种类胡萝卜素底物的详细催化活性需要进一步研究，参与类胡萝卜素和脱辅基类胡萝卜素代谢调控的关键转录因子需要阐明。
