State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, and College of Life Science and Technology, Guangxi University, Nanning, People's Republic of China.
PLoS One. 2012;7(12):e52646. doi: 10.1371/journal.pone.0052646. Epub 2012 Dec 21.
Biofilm formation and dispersal in the black rot pathogen Xanthomonas campestris pathovar campestris (Xcc) is influenced by a number of factors. The extracellular mannanase ManA has been implicated in biofilm dispersal whereas biofilm formation requires a putative glycosyl transferase encoded by the xag gene cluster. Previously we demonstrated that the post-transcriptional regulator RsmA exerts a negative regulatory influence on biofilm formation in Xcc. Here we address the mechanisms by which RsmA exerts this action. We show that RsmA binds to the transcripts of three genes encoding GGDEF domain diguanylate cyclases to influence their expression. Accordingly, mutation of rsmA leads to an increase in cellular levels of cyclic di-GMP. This effect is associated with a down-regulation of transcription of manA, but an upregulation of xag gene transcription. Mutation of clp, which encodes a cyclic di-GMP-responsive transcriptional regulator of the CRP-FNR family, has similar divergent effects on the expression of manA and xag. Nevertheless Clp binding to manA and xag promoters is inhibited by cyclic di-GMP. The data support the contention that, in common with other CRP-FNR family members, Clp can act as both an activator and repressor of transcription of different genes to influence biofilm formation as a response to cyclic di-GMP.
生物膜的形成和分散是受许多因素影响的。胞外甘露聚糖酶 ManA 被认为与生物膜分散有关，而生物膜的形成则需要 xag 基因簇编码的假定糖基转移酶。以前我们证明了转录后调节因子 RsmA 对 Xcc 中的生物膜形成有负调控作用。在这里，我们研究了 RsmA 发挥这种作用的机制。我们表明，RsmA 与三个编码 GGDEF 结构域二鸟苷酸环化酶的基因的转录本结合，从而影响它们的表达。因此，rsmA 的突变导致细胞中二环鸟苷酸 (cyclic di-GMP) 的水平增加。这种效应与 manA 的转录下调有关，但 xag 基因的转录上调有关。clp 编码 CRP-FNR 家族中对环二鸟苷酸有反应的转录调节因子，它对 manA 和 xag 的表达有类似的发散效应。然而，Clp 与 manA 和 xag 启动子的结合被环二鸟苷酸抑制。这些数据支持了这样一种观点，即与其他 CRP-FNR 家族成员一样，Clp 可以作为不同基因转录的激活剂和抑制剂，以响应环二鸟苷酸影响生物膜的形成。
