Comparison of transcriptional expression patterns of phenols and carotenoids in ‘Kyoho’ grapes under a two-crop-a-year cultivation system

To fully utilize the characteristic climatic conditions in the southern region of China, a two-crop-a-year cultivation system technique for ‘Kyoho’ grape was developed during the past decade. After summer harvest in June, appropriate pruning and chemical treatments promote flowering and fruiting, which enables a second harvest in late December. Due to climatic differences between the two crop growing seasons, grape phenol and carotenoid metabolism differ greatly. The reported study analyzed the transcriptome of the carotenoid and phenylpropanoid/flavonoid pathways in grapes at four different stages during the two growing seasons. Compared with those in summer grapes, expression levels of the majority of genes involved in the carotenoid metabolic pathway in winter grapes were generally upregulated. This result was associated with lower rainfall and much more abundant sunlight during the second growing season. On the other hand, summer cropping strongly triggered the expression of upstream genes in the phenylpropanoid/flavonoid pathway at E-L 33 and E-L 35. Transcript levels of flavonoid 3’,5’-hydroxylase (F3’5’H), flavonoid 3’-hydroxylase (F3’H), flavonoid 3-hydroxylase (F3H) and glutathione S-transferase (GST) were upregulated in winter grapes at the mature stage. Together, these results might indicate that more flavonoids would be synthesized in ripe winter grapes during the mature stage of the second crop under much drier conditions, longer sunlight hours and lower temperature. These data provide a theoretical foundation for the secondary metabolism of berries grown under two-crop-a-year cultivation systems.

为充分利用中国南方独特的气候条件，科研团队在近十年间开发了适用于巨峰（Kyoho）葡萄的一年两熟栽培技术。在6月完成夏季采收后，通过合理修剪与化学调控可促进植株再次开花结果，实现12月下旬的第二次采收。由于两季葡萄生育期的气候差异显著，葡萄的酚类代谢与类胡萝卜素代谢模式存在极大不同。本研究针对两季葡萄生育期内的四个不同阶段，分析了类胡萝卜素代谢通路与苯丙烷/类黄酮通路的转录组特征。与夏季采收的葡萄相比，冬季采收葡萄中类胡萝卜素代谢通路的绝大多数基因表达水平整体上调，该现象与第二季生育期内降雨量更少、光照更为充足的气候特征密切相关。另一方面，夏季栽培的葡萄在E-L 33与E-L 35阶段，其苯丙烷/类黄酮通路的上游基因表达被显著激活。在成熟阶段，冬季采收葡萄中类黄酮3',5'-羟化酶（F3’5’H）、类黄酮3'-羟化酶（F3’H）、类黄酮3-羟化酶（F3H）以及谷胱甘肽S-转移酶（GST）的转录水平均呈现上调。综合来看，这些结果表明，在第二季生育期的成熟阶段，当环境更为干燥、光照时长更长且温度更低时，成熟的冬季采收葡萄会合成更多的类黄酮物质。本研究数据为一年两熟栽培体系下浆果的次生代谢研究提供了理论依据。