Regulatory RNA as mediator in GacA/RsmA-dependent global control of exoproduct formation in Pseudomonas fluorescens CHA0
Regulatory RNA as mediator in GacA/RsmA-dependent global control of exoproduct formation in Pseudomonas fluorescens CHA0
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DOI：
10.1128/jb.184.4.1046-1056.2002
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发表时间：
2002-02-01
影响因子：
3.2
通讯作者：
Haas, D
中科院分区：
文献类型：
--
作者：
Heeb, S;Blumer, C;Haas, D
荧光假单胞菌（Pseudomonasfluorescens）的GacS/GacA双组分系统在转录后水平紧密控制抗真菌次生代谢产物和胞外酶的表达，涉及RNA结合蛋白和次生代谢全局调节因子RsmA。从荧光假单胞菌中纯化该蛋白质，并将与其结合的RNA转化为cDNA，其用作探针以分离相应的染色体基因座rsmZ。该基因编码127个核苷酸的调节RNA和3'端缺失35个核苷酸的截短形式。rsmZ的表达依赖于GacA，随着人口密度的增加而增加，并且通过添加由菌株CHA 0在指数生长结束时产生的溶剂可提取的细胞外信号来刺激。该信号似乎与N-酰基-高丝氨酸内酯无关。一个保守的上游元件在rsmZ启动子，但不是应力σ因子RpoS，参与rsmZ的表达。rsmZ的过表达有效地抑制了gacS和gacA突变对靶基因的负面影响，即，hcnA（代表氰化氢合成酶）和aprA（代表主要的外切蛋白酶）。rsmZ的突变失活导致这些靶基因在添加信号存在下的表达降低。rsmA的过表达也有类似的，但更强的负面影响。这些结果支持了一个模型，其中GacA上调调控RNA的表达，如菌株CHA 0的RsmZ，以响应细菌信号。通过滴定效应，RsmZ可以减轻RsmA对靶mRNA表达的抑制活性。
In Pseudomonas fluorescens CHA0, an antagonist of root-pathogenic fungi, the GacS/GacA two-component system tightly controls the expression of antifungal secondary metabolites and exoenzymes at a posttranscriptional level, involving the RNA-binding protein and global regulator of secondary metabolism RsmA. This protein was purified from P. fluorescens, and RNA bound to it was converted to cDNA, which served as a probe to isolate the corresponding chromosomal locus, rsmZ. This gene encoded a regulatory RNA of 127 nucleotides and a truncated form lacking 35 nucleotides at the 3' end. Expression of rsmZ depended on GacA, increased with increasing population density, and was stimulated by the addition of a solvent-extractable extracellular signal produced by strain CHA0 at the end of exponential growth. This signal appeared to be unrelated to N-acyl-homoserine lactones. A conserved upstream element in the rsmZ promoter, but not the stress sigma factor RpoS, was involved in rsmZ expression. Overexpression of rsmZ effectively suppressed the negative effect of gacS and gacA mutations on target genes, i.e., hcnA (for hydrogen cyanide synthase) and aprA (for the major exoprotease). Mutational inactivation of rsmZ resulted in reduced expression of these target genes in the presence of added signal. Overexpression of rsmA had a similar, albeit stronger negative effect. These results support a model in which GacA upregulates the expression of regulatory RNAs, such as RsmZ of strain CHA0, in response to a bacterial signal. By a titration effect, RsmZ may then alleviate the repressing activity of RsmA on the expression of target mRNAs.