Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, the Chinese Academy of Sciences, Guangzhou, 510650, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
J Integr Plant Biol. 2014 Nov;56(11):1034-41. doi: 10.1111/jipb.12211. Epub 2014 Jun 19.
The discovery of the enzyme L,L-diaminopimelate aminotransferase (LL-DAP-AT, EC 2.6.1.83) uncovered a unique step in the L-lysine biosynthesis pathway in plants. In Arabidopsis thaliana, LL-DAP-AT has been shown to play a key role in plant-pathogen interactions by regulation of the salicylic acid (SA) signaling pathway. Here, a full-length cDNA of LL-DAP-AT named as LjALD1 from Lotus japonicus (Regel) Larsen was isolated. The deduced amino acid sequence shares 67% identity with the Arabidopsis aminotransferase AGD2-LIKE DEFENSE RESPONSE PROTEIN1 (AtALD1) and is predicted to contain the same key elements: a conserved aminotransferase domain and a pyridoxal-5'-phosphate cofactor binding site. Quantitative real-time PCR analysis showed that LjALD1 was expressed in all L. japonicus tissues tested, being strongest in nodules. Expression was induced in roots that had been infected with the symbiotic rhizobium Mesorhizobium loti or treated with SA agonist benzo-(1, 2, 3)-thiadiazole-7-carbothioic acid. LjALD1 Knockdown exhibited a lower SA content, an increased number of infection threads and nodules, and a slight reduction in nodule size. In addition, compared with wild-type, root growth was increased and shoot growth was suppressed in LjALD1 RNAi plant lines. These results indicate that LjALD1 may play important roles in plant development and nodulation via SA signaling in L. japonicus.
酶 L,L-二氨基庚二酸氨基转移酶（LL-DAP-AT，EC 2.6.1.83）的发现揭示了植物中赖氨酸生物合成途径的一个独特步骤。在拟南芥中，LL-DAP-AT 通过调节水杨酸（SA）信号通路在植物-病原体相互作用中发挥关键作用。在这里，从 Lotus japonicus（Regel）Larsen 中分离出全长 cDNA 的 LL-DAP-AT，命名为 LjALD1。推导的氨基酸序列与拟南芥氨基转移酶 AGD2-LIKE DEFENSE RESPONSE PROTEIN1（AtALD1）具有 67%的同一性，并且预计包含相同的关键元素：保守的氨基转移酶结构域和吡哆醛-5'-磷酸辅因子结合位点。定量实时 PCR 分析表明，LjALD1 在所有测试的 L. japonicus 组织中表达，在根瘤中表达最强。在被共生根瘤菌 Mesorhizobium loti 感染或用 SA 激动剂苯并-（1,2,3）-噻二唑-7-碳硫代羧酸处理的根中诱导表达。LjALD1 敲低表现出较低的 SA 含量、增加的侵染线和根瘤数量，以及根瘤大小略有减少。此外，与野生型相比，LjALD1 RNAi 植物系的根生长增加，茎生长受到抑制。这些结果表明，LjALD1 可能通过 L. japonicus 中的 SA 信号在植物发育和结瘤中发挥重要作用。
