Table_3_Genome-Wide Identification of Tannase Genes and Their Function of Wound Response and Astringent Substances Accumulation in Juglandaceae.XLSX

Tannins are important polyphenol compounds with different component proportions in different plant species. The plants in the Juglandaceae are rich in tannins, including condensed tannins and hydrolyzable tannins. In this study, we identified seven tannase genes (TAs) responsible for the tannin metabolism from walnut, pecan, and Chinese hickory, and three nut tree species in the Juglandaceae, which were divided into two groups. The phylogenetic and sequence analysis showed that TA genes and neighboring clade genes (TA-like genes) had similar sequences compared with other carboxylesterase genes, which may be the origin of TA genes produced by tandem repeat. TA genes also indicated higher expressions in leaf than other tissues and were quickly up-regulated at 3 h after leaf injury. During the development of the seed coat, the expression of the synthesis-related gene GGTs and the hydrolase gene TAs was continuously decreased, resulting in the decrease of tannin content in the dry sample of the seed coat of Chinese hickory. However, due to the reduction in water content during the ripening process, the tannin content in fresh sample increased, so the astringent taste was obvious at the mature stage. In addition, the CcGGTs’ expression was higher than CiGGTs in the initiation of development, but CcTAs continued to be down-regulated while CiTA2a and CiTA2b were up-regulated, which may bring about the significant differences in tannin content and astringent taste between Chinese hickory and pecan. These results suggested the crucial role of TAs in wound stress of leaves and astringent ingredient accumulation in seed coats of two nut tree species in the Juglandaceae.

单宁是一类重要的多酚类化合物，不同植物物种中其组分占比存在显著差异。胡桃科（Juglandaceae）植物富含单宁，包括缩合单宁与水解单宁。本研究从核桃、薄壳山核桃以及中国山核桃这3种胡桃科坚果树种中，鉴定得到7个参与单宁代谢的单宁酶基因（TAs），并将其划分为两个类群。系统发育与序列分析结果显示，相较于其他羧酸酯酶基因，单宁酶基因及其近缘分支基因（TA-like genes）序列相似度较高，推测单宁酶基因可能通过串联重复事件起源。此外，单宁酶基因在叶片中的表达量显著高于其他组织，且在叶片受损3小时后即快速上调表达。在种皮发育过程中，合成相关基因γ-谷氨酰转移酶（GGTs）与水解酶基因TAs的表达量持续下降，导致中国山核桃种皮干样品中的单宁含量降低。但在果实成熟进程中，由于水分含量不断减少，鲜样品中的单宁含量反而升高，因此成熟阶段的涩味表现较为明显。另外，在发育起始阶段，CcGGTs的表达量高于CiGGTs，而CcTAs的表达量持续下调，CiTA2a与CiTA2b则呈上调趋势，这可能是造成中国山核桃与薄壳山核桃间单宁含量及涩味存在显著差异的关键原因。上述结果表明，单宁酶基因在两种胡桃科坚果树种的叶片创伤胁迫响应以及种皮涩味物质积累过程中发挥着关键作用。