Transcriptomic Studies Reveal that the Rhizobium leguminosarum Serine/Threonine Protein Phosphatase PssZ has a Role in the Synthesis of Cell-Surface Components, Nutrient Utilization, and Other Cellular Processes

Abstract

Rhizobium leguminosarum bv. trifolii is a soil bacterium capable of establishing symbiotic associations with clover plants (Trifolium spp.). Surface polysaccharides, transport systems, and extracellular components synthesized by this bacterium are required for both the adaptation to changing environmental conditions and successful infection of host plant roots. The pssZ gene located in the Pss-I region, which is involved in the synthesis of extracellular polysaccharide, encodes a protein belonging to the group of serine/threonine protein phosphatases. In this study, a comparative transcriptomic analysis of R. leguminosarum bv. trifolii wild-type strain Rt24.2 and its derivative Rt297 carrying a pssZ mutation was performed. RNA-Seq data identified a large number of genes differentially expressed in these two backgrounds. Transcriptome profiling of the pssZ mutant revealed a role of the PssZ protein in several cellular processes, including cell signalling, transcription regulation, synthesis of cell-surface polysaccharides and components, and bacterial metabolism. In addition, we show that inactivation of pssZ affects the rhizobial ability to grow in the presence of different sugars and at various temperatures, as well as the production of different surface polysaccharides. In conclusion, our results identified a set of genes whose expression was affected by PssZ and confirmed the important role of this protein in the rhizobial regulatory network.

Rhizobial Exopolysaccharides: Genetic Regulation of Their Synthesis and Relevance in Symbiosis With Legumes

“…japonicus. According to Stacey et al [21] this difference may be due to the fact that IT of Transcription of pssA in both ex planta and in planta is at a low level, indicating that the expression of this gene, which is crucial for EPS synthesis, is under very stringent regulation [41,[53][54][55].…”

“…trifolii [73]. Comparative transcriptomic analysis of the pssZ mutant and the wild-type strain identified a large number of genes differentially expressed in these two backgrounds, including genes related with several cellular processes (signalling, transcription regulation, synthesis of cell-surface polysaccharides, cell division and motility, bacterial metabolism) [55]. Interestingly, expression of almost all pss genes located in the Pss-I region was totally inhibited in the pssZ mutant.…”

Identification of Ensifer meliloti genes required for survival during peat-based bioinoculant maturation by STM-seq

“…Genes in this group included SM_b21213-pphA, a gene coding for a putative serine/threonine protein phosphatase (STPs) homologous to PssZ from Rhizobium leguminosarum bv trifolii Rt24.2; whose mutation causes pleiotropic effects including the lack of EPS production, reduced growth kinetics and motility, and failure in host root infection (Lipa et al, 2019(Lipa et al, , 2018. Another key gene for PI survival was fixL, the histidine kinase of the FixL-FixJ two-component system.…”

Rhizobial Exopolysaccharides: Genetic Regulation of Their Synthesis and Relevance in Symbiosis with Legumes

“…Mutations in pssA totally abolish EPS synthesis, leading to the induction of empty (without bacteria), non-nitrogen-fixing root nodules on host plants (clover, pea and vetch) [44,[54][55][56][57][58]. The transcription of pssA in both ex planta and in planta conditions is at a low level, indicating that the expression of this gene, which is crucial for EPS synthesis, is under very stringent regulation [44,[59][60][61]. All pss genes involved in subsequent steps of the EPS subunit synthesis belong to the Pss-I region.…”

“…trifolii [79]. Comparative transcriptomic analysis of the pssZ mutant and the wild-type strain identified a large number of genes differentially expressed in these two backgrounds, including genes related to several cellular processes (signalling, transcription regulation, synthesis of cell-surface polysaccharides, cell division and motility, bacterial metabolism) [61]. Interestingly, expression of almost all pss genes located in the Pss-I region was totally inhibited in the pssZ mutant.…”