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

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 () 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 genes and neighboring clade genes ( genes) had similar sequences compared with other carboxylesterase genes, which may be the origin of genes produced by tandem repeat. 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 and the hydrolase gene 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 ' expression was higher than in the initiation of development, but continued to be down-regulated while and 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 in wound stress of leaves and astringent ingredient accumulation in seed coats of two nut tree species in the Juglandaceae.