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J Exp Bot. 2016 Oct;67(19):5869-5884. Epub 2016 Oct 4.

A rhamnose-deficient lipopolysaccharide mutant of Rhizobium sp. IRBG74 is defective in root colonization and beneficial interactions with its flooding-tolerant hosts Sesbania cannabina and wetland rice.

Author information

1
Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 USA.
2
Department of Agronomy, University of Wisconsin-Madison, Madison, WI, USA.
3
The Energy and Resources Institute, New Delhi 110003, India.
4
Department of Agronomy, University of Wisconsin-Madison, Madison, WI, USA Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA prasadg@uwm.edu Euan.James@hutton.ac.uk jeanmichel.ane@wisc.edu.
5
The James Hutton Institute, Dundee DD2 5DA, UK prasadg@uwm.edu Euan.James@hutton.ac.uk jeanmichel.ane@wisc.edu.
6
Department of Biological Sciences, University of Wisconsin-Milwaukee, Milwaukee, WI 53211 USA prasadg@uwm.edu Euan.James@hutton.ac.uk jeanmichel.ane@wisc.edu.

Abstract

Rhizobium sp. IRBG74 develops a classical nitrogen-fixing symbiosis with the aquatic legume Sesbania cannabina (Retz.). It also promotes the growth of wetland rice (Oryza sativa L.), but little is known about the rhizobial determinants important for these interactions. In this study, we analyzed the colonization of S. cannabina and rice using a strain of Rhizobium sp. IRBG74 dually marked with β-glucuronidase and the green fluorescent protein. This bacterium colonized S. cannabina by crack entry and through root hair infection under flooded and non-flooded conditions, respectively. Rhizobium sp. IRBG74 colonized the surfaces of wetland rice roots, but also entered them at the base of lateral roots. It became endophytically established within intercellular spaces in the rice cortex, and intracellularly within epidermal and hypodermal cells. A mutant of Rhizobium sp. IRBG74 altered in the synthesis of the rhamnose-containing O-antigen exhibited significant defects, not only in nodulation and symbiotic nitrogen fixation with S. cannabina, but also in rice colonization and plant growth promotion. Supplementation with purified lipopolysaccharides from the wild-type strain, but not from the mutant, restored the beneficial colonization of rice roots, but not fully effective nodulation of S. cannabina Commonalities and differences in the rhizobial colonization of the roots of wetland legume and rice hosts are discussed.

KEYWORDS:

GFP; GUS; lateral root base (LRB) entry; lipopolysaccharide (LPS); nitrogen fixation; plant growth-promoting rhizobacteria (PGPRs).

PMID:
27702995
DOI:
10.1093/jxb/erw354
[Indexed for MEDLINE]

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