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Front. Microbiol. | doi: 10.3389/fmicb.2018.03046

Mutagenesis of PhaR, a Regulator Gene of Polyhydroxyalkanoate Biosynthesis of Xanthomonas oryzae pv. oryzae Caused Pleiotropic Phenotype Changes

 Juying Long1, Kang li Song1, Xiang He1, Xiaofang Cui1, Bin Zhang1 and  Congfeng Song1*
  • 1Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, China

Polyhydroxyalkanoates (PHAs) are intracellular carbon and energy storage materials produced in various microorganisms under nutrient-limited conditions. PhaR is a regulatory protein involved in PHA synthesis. Xanthomonas oryzae pv. oryzae (Xoo ) is one of the most important bacterial pathogens in rice and has PHA biosynthesis genes in its genome, but the biological function of phaR in Xoo is unknown. In this study, we investigated the effects of the mutagenesis of phaR gene in Xoo strain PXO99A. Compared to the wild type, the PhaR gene knock-out mutant PXO99phaR was hypermotile and showed decreased growth rates in both rich and limited nutrient media. PXO99phaR also showed almost 75% decrease in extracellular polysaccharide (EPS) production. When inoculated in rice leaves by leaf-clipping method, PXO99phaR displayed reduced virulence in terms of lesion length and bacterial multiplication compared with the wild type strain. PXO99phaR also showed enhanced hypersensitive response (HR) induction in the leaves of nonhost Nicotiana benthamiana with elevated hpa1 gene expression. Introduction of a cosmid containing the phaR coding sequence restored the phenotypes of the mutant to those of the wildtype strain. These results suggest that PhaR gene is an important gene that affects multiple bacterial characteristics, including EPS production, growth rate, defense response induced harpin production and motility, related to its virulence in plant.

Keywords: Xanthomonas oryzae pv. oryzae, polyhydroxyalkanoate regulator, phaR gene, Virulence, motility, hypersensitive response, hpa1 gene

Received: 09 Aug 2018; Accepted: 27 Nov 2018.

Edited by:

Camille E. Granada, University of Taquari Valley, Brazil

Reviewed by:

Akanksha Singh, Central Institute of Medicinal and Aromatic Plants (CIMAP), India
Kaijun Zhao, Institute of Crop Sciences (CAAS), China
Luiz G. Borges, Icahn School of Medicine at Mount Sinai, United States  

Copyright: © 2018 Long, Song, He, Cui, Zhang and Song. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Congfeng Song, Department of Plant Pathology, College of Plant Protection, Nanjing Agricultural University, Nanjing, China, cfsong@njau.edu.cn