Department of Plant Pathology, Plant Protection College, Shenyang Agricultural University, Shenyang 110866, China.
State Key Laboratory for Biology of Plant Diseases and Insect Pests, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China.
Int J Mol Sci. 2022 Aug 25;23(17):9632. doi: 10.3390/ijms23179632.
A type VI secretion system (T6SS) gene cluster has been reported in . Research on the activation conditions, functions, and the interactions between key elements in . T6SS is lacking. Hcp (Hemolysin co-regulated protein) is both a structural protein and a secretion protein of T6SS, which makes it a special element. The aims of this study were to determine the role of Hcp and its activated conditions to reveal the functions of T6SS. In virulence and colonization assays of deletion mutant strain Δ, (type VI secretion system membrane subunit) deletion mutant strain Δ and double mutant ΔΔ, population growth was affected but not virulence after injection of cotyledons and seed-to-seedling transmission on watermelon. The population growth of Δ and Δ were lower than wild type strain Aac5 of group II at early stage but higher at a later stage. Deletion of also affected growth ability in different culture media, and the decline stage of Δ was delayed in KB medium. Biofilm formation ability of Δ, Δ and ΔΔ was lower than Aac5 with competition by prey bacteria but higher in KB and M9-Fe medium. Deletion of reduced the competition and survival ability of Aac5. Based on the results of Western blotting and qRT-PCR analyses, Hcp is activated by cell density, competition, ferric irons, and the host plant. The expression levels of genes related to bacterial secretion systems, protein export, and several other pathways, were significantly changed in the Δ mutant compared to Aac5 when T6SS was activated at high cell density. Based on transcriptome data, we found that a few candidate effectors need further identification. The phenotypes, activated conditions and transcriptome data all supported the conclusion that although there is only one T6SS gene cluster present in the . group II strain Aac5, it related to multiple biological processes, including colonization, growth ability, competition and biofilm formation.
一种 VI 型分泌系统（T6SS）基因簇已在 中报道。关于 T6SS 的激活条件、功能以及关键要素之间的相互作用的研究还很缺乏。Hcp（溶血素共调节蛋白）既是 T6SS 的结构蛋白又是分泌蛋白，这使其成为一个特殊的元素。本研究旨在确定 Hcp 的作用及其激活条件，以揭示 T6SS 的功能。在毒性和定植测定中， 缺失突变株Δ、T6SS 膜亚基缺失突变株Δ和双突变株ΔΔ，在向西瓜子叶注射和种子到种子传播后，群体生长受到影响，但毒力没有受到影响。Δ和Δ的种群增长在早期低于 II 组的野生型菌株 Aac5，但在后期较高。缺失 也影响了不同培养基中的生长能力，并且在 KB 培养基中Δ的下降阶段被延迟。Δ、Δ和ΔΔ的生物膜形成能力低于具有捕食细菌竞争的 Aac5，但在 KB 和 M9-Fe 培养基中较高。缺失 降低了 Aac5 的竞争和生存能力。基于 Western blot 和 qRT-PCR 分析的结果，Hcp 被细胞密度、竞争、三价铁和宿主植物激活。与 Aac5 相比，当 T6SS 在高细胞密度下被激活时，Δ 突变体中与细菌分泌系统、蛋白输出和其他几种途径相关的基因的表达水平发生了显著变化。基于转录组数据，我们发现一些候选效应物需要进一步鉴定。表型、激活条件和转录组数据都支持这样的结论，即在 II 组菌株 Aac5 中虽然只存在一个 T6SS 基因簇，但它与包括定植、生长能力、竞争和生物膜形成在内的多种生物学过程有关。
