CEA, DSV, IBEB, SBVME, Laboratoire d’Ecologie Microbienne de la Rhizosphère et d’Environnements Extrèmes (LEMiRE), Saint-Paul-lez-Durance, France.
Appl Environ Microbiol. 2012 Mar;78(6):1658-65. doi: 10.1128/AEM.06769-11. Epub 2012 Jan 13.
The plant-beneficial bacterium Pseudomonas brassicacearum forms phenotypic variants in vitro as well as in planta during root colonization under natural conditions. Transcriptome analysis of typical phenotypic variants using microarrays containing coding as well as noncoding DNA fragments showed differential expression of several genes relevant to secondary metabolism and of the small RNA (sRNA) genes rsmX, rsmY, and rsmZ. Naturally occurring mutations in the gacS-gacA system accounted for phenotypic switching, which was characterized by downregulation of antifungal secondary metabolites (2,4-diacetylphloroglucinol and cyanide), indoleacetate, exoenzymes (lipase and protease), and three different N-acyl-homoserine lactone molecules. Moreover, in addition to abrogating these biocontrol traits, gacS and gacA mutations resulted in reduced expression of the type VI secretion machinery, alginate biosynthesis, and biofilm formation. In a gacA mutant, the expression of rsmX was completely abolished, unlike that of rsmY and rsmZ. Overexpression of any of the three sRNAs in the gacA mutant overruled the pleiotropic changes and restored the wild-type phenotypes, suggesting functional redundancy of these sRNAs. In conclusion, our data show that phenotypic switching in P. brassicacearum results from mutations in the gacS-gacA system.
植物有益细菌假单胞菌在自然条件下根定植过程中会在体外和体内形成表型变体。使用含有编码和非编码 DNA 片段的微阵列对典型表型变体进行转录组分析表明，与次级代谢和小 RNA (sRNA) 基因 rsmX、rsmY 和 rsmZ 相关的几个基因的表达存在差异。gacS-gacA 系统中的自然发生突变导致表型转换，其特征是下调抗真菌次级代谢物（2,4-二乙酰基邻苯二酚和氰化物）、吲哚乙酸、外切酶（脂肪酶和蛋白酶）和三种不同的 N-酰基高丝氨酸内酯分子。此外，除了消除这些生物防治特性外，gacS 和 gacA 突变还导致 VI 型分泌机制、海藻酸盐生物合成和生物膜形成的表达减少。在 gacA 突变体中，rsmX 的表达完全被废除，而 rsmY 和 rsmZ 的表达则不然。在 gacA 突变体中过表达这三种 sRNA 中的任何一种都可以推翻多效性变化并恢复野生型表型，这表明这些 sRNA 具有功能冗余性。总之，我们的数据表明，假单胞菌中的表型转换是由 gacS-gacA 系统中的突变引起的。
