Institute of Agriculture and Life Science, Gyeongsang National University, Jinju, 52828, South Korea.
Department of Plant Medicine, Gyeongsang National University, Jinju, South Korea.
Microb Biotechnol. 2021 Jul;14(4):1657-1670. doi: 10.1111/1751-7915.13831. Epub 2021 May 19.
The toxoflavin (Txn), broad host range phytotoxin produced by a variety of bacteria, including Burkholderia glumae, is a key pathogenicity factor of B. glumae in rice and field crops. Two bacteria exhibiting Txn-degrading activity were isolated from healthy rice seeds and identified as Sphingomonas adhaesiva and Agrobacterium sp. respectively. The genes stdR and stdA, encoding proteins responsible for Txn degradation of both bacterial isolates, were identical, indicating that horizontal gene transfer occurred between microbial communities in the same ecosystem. We identified a novel Txn-quenching regulation of bacteria, demonstrating that the LysR-type transcriptional regulator (LTTR) StdR induces the expression of the stdA, which encodes a Txn-degrading enzyme, in the presence of Txn as a coinducer. Here we show that the bacterial StdR -quenching regulatory system mimics the ToxR -mediated biosynthetic regulation of B. glumae. Substrate specificity investigations revealed that Txn is the only coinducer of StdR and that StdA has a high degree of specificity for Txn. Rice plants expressing StdA showed Txn resistance. Collectively, bacteria mimic the mechanism of Txn biosynthesis regulation, employ it in the development of a Txn-quenching regulatory system and share it with neighbouring bacteria for survival in rice environments full of Txn.
类脂环酸内酯（Txn）是一种广泛宿主范围的植物毒素，由多种细菌产生，包括稻生欧文氏菌（Burkholderia glumae），是该菌在水稻和大田作物中致病的关键因素。从健康水稻种子中分离到两种具有 Txn 降解活性的细菌，分别鉴定为粘质沙雷氏菌（Sphingomonas adhaesiva）和根癌农杆菌（Agrobacterium sp.）。编码这两种细菌 Txn 降解蛋白的 stdR 和 stdA 基因完全相同，表明同一生态系统中微生物群落间发生了水平基因转移。我们发现了一种新的细菌 Txn 猝灭调控机制，证明 LysR 型转录调节因子（LTTR）StdR 在 Txn 作为共诱导剂存在的情况下诱导编码 Txn 降解酶的 stdA 的表达。本研究表明，细菌 StdR 猝灭调节系统模拟了稻生欧文氏菌的 ToxR 介导的生物合成调控。底物特异性研究表明，Txn 是 StdR 的唯一共诱导剂，而 StdA 对 Txn 具有高度特异性。表达 StdA 的水稻植株表现出对 Txn 的抗性。综上所述，细菌模拟了 Txn 生物合成调控的机制，将其用于开发 Txn 猝灭调节系统，并与邻近细菌共享该系统，以在富含 Txn 的水稻环境中生存。
