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

Abstract

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.

Valorization of Traditional Italian Walnut (Juglans regia L.) Production: Genetic, Nutritional and Sensory Characterization of Locally Grown Varieties in the Trentino Region

“…Ellagitannins are among the major phenolic classes determined in walnuts [ 6 , 7 , 8 ] and have been reported to act as strong astringents [ 52 ]. This is consistent with our results, where the low polyphenols concentration observed for the commercial cultivar ‘Lara’ supports the characteristic low level of bitterness described by Germain et al [ 53 ] and also reported in the sensory study of Colaric et al [ 54 ] for this cultivar.…”

“…In previous studies, ‘Lara’ was reported among the least bitter and astringent walnut cultivars [ 53 , 54 ]; conversely, the higher level of polyphenols observed for ‘Blegette’ suggests a stronger astringency [ 49 , 52 ]. Our results indicate a certain degree of variability in consumer perception of the taste properties of walnut kernels, as previously reported by Colarič and colleagues [ 54 ].…”

Regulation of Plant Tannin Synthesis in Crop Species

“…The work of Dai et al (2020) revealed that transient overexpression and RNAi of a strawberry tannase ( FaTA ) provoke an alteration in ellagic acid content; in addition, several enzymes belonging to the class I carboxylesterase clade were identified in V. vinifera , J. regia , Citrus clementine, D. kaki, and C. sinensis , indicating the hypothetical existence of more tannase genes in plants. A recent work in Juglandaceae ( Wang et al, 2021 ) reveals regulatory cis -elements found in tannase promoters: E-box and ARR1AT, involved in brassinolide and cytokine responsiveness, respectively, and W-box and WUN-motifs implicated in wound abiotic stress responses. Also, motifs related to flavonoid biosynthesis (MYB-related motifs) and MYC motifs, related to cell growth, were found in tannases from Chinese hickory ( Carya cathayensis ) and pecan ( Carya illinoinensis ).…”

Metabolome and Transcriptome Profiling Unveil the Mechanisms of Polyphenol Synthesis in the Developing Endopleura of Walnut (Juglans regia L.)

“…The polyphenols in walnut kernels have an important effect on quality. Some polyphenols can bind to the proteins in human saliva, giving and astringent taste [ 4 ], and the oxidation and degradation of polyphenols will change the color of walnut kernels. In addition, polyphenols have a strong anti-free radical ability, which can enhance immunity, provide resistance against atherosclerosis, and protect eyesight [ 5 ].…”