[Frontiers in Bioscience E4, 1263-1275, January 1, 2012]

Role of the RNA-binding protein Hfq in Serratia plymuthica

Min Zhou1, Kexiang Gao2, Jun Zeng1, Xiaoli Yu1, Yan Wu1, Jun Ge1, Yunfei Duan1, Xiaoguang Liu1

1Institute of Life Sciences, Jiangsu University, Zhenjiang 212013, China, 2Department of Plant Pathology, Shandong Agricultural University, Taian 271018, China

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and Methods
3.1. Microorganism strains, plasmids and growth conditions
3.2. DNA preparation and manipulations
3.3. Cloning and sequencing of the hfq gene from S. plymuthica strain G3
3.4. Phylogenetic analysis
3.5. Mutant construction and complementation
3.6. Phenotypic analysis
3.6.1. Biocontrol-related phenotypes
3.6.2. Quantification of IAA production
3.6.3. TLC detection of PRN production and bioassay
3.7. Construction and analysis of lux-based and lacZ-based fusions
3.8. Nucleotide sequence accession number
4. Results
4.1. Cloning of the S. plymuthica G3 hfq gene
4.2. Construction of a S. plymuthica hfq mutant and complementation
4.3. Loss of Hfq results in growth defects of S. plymuthica G3
4.4. Hfq is required for expression of variety of biocontrol-related phenotypes
4.5. Hfq positively regulates accumulation of IAA by G3
4.6. Hfq controls PRN production at the both transcriptional and translational levels
4.7. Hfq is required for the expression of the rpoS gene
4.8. Hfq is positively autoregulated by itself
5. Discussion
6. Acknowledgement
7. References

1. ABSTRACT

The RNA-binding protein Hfq has been well studied as a global post-transcriptional regulator which controls diverse cellular processes in bacteria. However, the function in the genus of Serratia has remained unexplored. Here we show that beyond mutation in Hfq resulting in their growth defects, Hfq has global effects on a variety of biocontrol-related phenotypes in the endophytic strain G3 of Serratia plymuthica, including antifungal activity, production of exoenzymes, as well as motility and biofilm formation. Especially for the first time, Hfq is observed to control biosynthesis of auxin indole-3-acetic acid (IAA) and antibiotic pyrrolnitrin (PRN), which are key determinants responsible for plant growth promotion and suppression of phytopathogens, respectively by G3. Additionally, Hfq is also required for the production of RpoS, a major stress sigma factor in G3. In contrast to E. coli, translation of hfq in G3 is positively autoregulated. Further investigation of the molecular mechanisms involved in regulation of IAA and pyrrolnitrin production by Hfq and its role in the regulatory networks of G3 will help to optimize the beneficial plant-microbe interactions.