Role of DEAD-box RNA helicases in low-temperature adapted growth of Antarctic Pseudomonas syringae Lz4W

Abstract

ABSTRACT Pseudomonas syringae possesses genes for all five major DEAD-box RNA helicases, rhlE, srmB, csdA, dbpA, and rhlB, that are found in γ-proteobacteria. Bioinformatic analysis of the RNA helicase genes provided detailed insights into their genomic organization, promoter characteristics, regulatory 3′ regions, and sequence similarity. Disruption of rhlB and rhlE genes did not have any effect on growth of the P. syringae mutants at optimum (22°C) or at low (4°C) temperatures. On the other hand, disruption of srmB and dbpA genes caused a slow-growing phenotype in the mutants at low temperature (4°C). In comparison to the above-mentioned helicases, deletion of csdA gene caused the mutant (ΔcsdA) to be totally incapable of growing at 4°C while marginally affecting the growth (resulting in slow growth) at the optimum temperature (22°C). Functional complementation studies revealed that RNA helicases are functionally non-redundant, as the roles performed by different helicases are individual and specific. IMPORTANCE RNA metabolism is important as RNA acts as a link between genomic information and functional biomolecules, thereby playing a critical role in cellular response to environment. We investigated the role of DEAD-box RNA helicases in low-temperature adapted growth of P. syringae, as this group of enzymes play an essential role in modulation of RNA secondary structures. This is the first report on the assessment of all major DEAD-box RNA helicases in any Antarctic bacterium. Of the five RNA helicases, three (srmB, csdA, and dbpA) are important for the growth of the Antarctic P. syringae at low temperature. However, the requisite role of dbpA and the indispensable requirement of csdA for low-temperature adapted growth are a novel finding of this study. Growth analysis of combinatorial deletion strains was performed to understand the functional interaction among helicase genes. Similarly, genetic complementation of RNA helicase mutants was conducted for identification of gene redundancy in P. syringae.

Keywords

• cold adaptation
• RNA helicases
• gene disruption
• homologous recombination
• growth analysis
• functional complementation