Alanine contributes to the taste and nutritional quality of tea and is an important member of alanine metabolism catalyzed by alanine aminotransferase (AlaAT, EC 2.6.1.2). However, the molecular mechanism underlying alanine metabolism in tea plants has not been fully elucidated. In this study, an increase in enzyme activity of AlaAT2 was detected in vitro, and the alanine aminotransferase activity was higher level in leaves than that in other tissues of tea plant, while the CsAlaAT2 transcription was high in leaves and root. Using phylogenetic analysis, an alanine aminotransferase gene CsAlaAT2 was identified as a member of group C, which was located in the mitochondrion. Additionally, the molecular mass of CsAlaAT2 protein was found to be approximately 53 kDa by SDS-PAGE and western blotting. The CsAlaAT2 expression level and the alanine content in photosynthetic tissues increased in response to the shade treatment. Furthermore, the involvement of CsAlaAT2 in alanine biosynthesis was confirmed based on transient suppression assays in tea leaves, and the alanine content and CsAlaAT2 transcript level decreased when CsAlaAT2 expression was suppressed in tea leaves. Thus, this study suggests that CsAlaAT2 is essential for the alanine metabolism in tea plants grown and its response to shade.

丙氨酸有助于茶的味道和营养品质，并且是丙氨酸氨基转移酶催化的丙氨酸代谢的重要成员（AlaAT，EC 2.6.1.2）。但是，尚未完全阐明茶树中丙氨酸代谢的分子机制。在这项研究中，在体外检测到AlaAT2的酶活性增加，并且叶片中的丙氨酸氨基转移酶活性高于茶树其他组织中的水平，而叶片和根中的CsAlaAT2转录较高。使用系统发育分析，丙氨酸转氨酶基因CsAlaAT2被鉴定为位于线粒体中的C组成员。另外，通过SDS-PAGE和蛋白质印迹发现CsAlaAT2蛋白的分子量约为53kDa。光合作用组织中的CsAlaAT2表达水平和丙氨酸含量响应于遮光处理而增加。此外，通过瞬时抑制测定法证实了茶叶中CsAlaAT2参与了丙氨酸的生物合成，并且当茶叶中的CsAlaAT2表达被抑制时，丙氨酸含量和CsAlaAT2转录水平降低。因此，该研究表明CsAlaAT2对于茶树生长中的丙氨酸代谢及其对阴影的响应至关重要。