Zhang Chun, Pang Qiuying, Jiang Luguang, Wang Shoucai, Yan Xiufeng, Chen Sixue, He Yan
National Maize Improvement Centre of China, Beijing Key Laboratory of Crop Genetic Improvement, China Agricultural University, Beijing, China.
Alkali Soil Natural Environmental Science Centre, Key Laboratory of Saline-alkali Vegetation Ecology Restoration in Oil Field, Northeast Forestry University, Harbin, Heilongjiang, China.
J Exp Bot. 2015 Feb;66(3):879-88. doi: 10.1093/jxb/eru449. Epub 2014 Nov 13.
Dihydroxyacid dehydratase (DHAD) catalyses a key step in the branched-chain amino acid (BCAA) biosynthetic pathway that exists in numerous organisms, including bacteria, fungi, and plants, but not humans. In Arabidopsis thaliana, DHAD is encoded by a single gene (AT3G23940), but its biological function in controlling plant development remains uncharacterized. In this study, we showed that DHAD is highly expressed in most vegetative and reproductive tissues. It is an essential gene, and complete disruption caused partial sterility in both male and female gametophyte phases. In addition, reduced expression of DHAD in knockdown mutants resulted in a reduction in the accumulation of all three BCAAs in roots and, as a consequence, led to a shorter root phenotype, which could be restored by an exogenous supplement of free BCAAs. Interestingly, the knockdown mutants became hypersensitive to salt stress, not to heavy metal stress, implying that BCAAs may act as osmolytes in salt tolerance. This would be the second amino acid shown to confer such a function in addition to the well-documented proline. Our results provide evidence that BCAA biosynthesis plays important roles in gametophyte and root development, and BCAA homeostasis contributes to the adaptation of Arabidopsis to salinity stress.
二羟酸脱水酶（DHAD）催化存在于包括细菌、真菌和植物但不包括人类在内的众多生物体中的支链氨基酸（BCAA）生物合成途径中的关键步骤。在拟南芥中，DHAD由单个基因（AT3G23940）编码，但其在控制植物发育中的生物学功能仍未得到表征。在本研究中，我们表明DHAD在大多数营养组织和生殖组织中高度表达。它是一个必需基因，完全破坏会导致雄配子体和雌配子体阶段的部分不育。此外，敲除突变体中DHAD表达的降低导致根中所有三种BCAAs的积累减少，结果导致根表型变短，这可以通过外源补充游离BCAAs来恢复。有趣的是，敲除突变体对盐胁迫变得超敏感，而对重金属胁迫不敏感，这意味着BCAAs可能作为渗透调节物质参与耐盐性。除了已充分证明的脯氨酸外，这将是第二种显示具有这种功能的氨基酸。我们的结果提供了证据，表明BCAA生物合成在配子体和根发育中起重要作用，并且BCAA稳态有助于拟南芥适应盐胁迫。
