Affiliation:
1. Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
Abstract
ABSTRACT
This study focuses on the function of the gene
praR
that encodes a putative transcription factor in
Azorhizobium caulinodans
ORS571, a microsymbiont of
Sesbania rostrata
. The
praR
gene is a homolog of the
phrR
gene of
Sinorhizobium medicae
WSM419, and the
praR
and
phrR
homologs are distributed throughout the class
Alphaproteobacteria
. The growth and nitrogen fixation activity of an
A. caulinodans praR
deletion mutant in the free-living state were not significantly different from those of the wild-type strain. However, the stem nodules formed by the
praR
mutant showed lower nitrogen fixation activity than the wild-type stem nodules. Microscopy revealed that infected host cells with an oval or elongated shape were observed at early stages in the nodules formed by the
praR
mutant, but these infected cells gradually fell into two types. One maintained an oval or elongated shape, but the vacuoles in these cells gradually enlarged and the bacteria gradually disappeared. The other cells were shrunken with bacteria remaining inside. Microarrays revealed that genes homologous to the
reb
genes of
Caedibacter taeniospiralis
were highly expressed in the
praR
mutant. Furthermore, the stem nodules formed by an
A. caulinodans
mutant with a deletion of
praR
and
reb
-homologous genes showed high nitrogen fixation activity, comparable to that of the wild-type stem nodules, and were filled with oval or elongated host cells. These results suggest that PraR controls the expression of the
reb
-homologous genes and that high expression of
reb
-homologous genes causes aberrance in
A. caulinodans
-
S. rostrata
symbiosis.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
23 articles.
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