Title |
Role of the extracytoplasmic function sigma factor CarQ in oxidative response of Bradyrhizobium japonicum |
Author |
Anchana Thaweethawakorn1, Dylan Parks1, Jae-Seong So2, and Woo-Suk Chang1,3* |
Address |
1Department of Biology, University of Texas, Arlington, Texas 76019, USA, 2Department of Biological Engineering, Inha University, Incheon 402-751, Republic of Korea, 3Division of Biotechnology, College of Environmental and Bioresource Sciences, Chonbuk National University, Iksan 570-752, Republic of Korea |
Bibliography |
Journal of Microbiology, 53(8),526-534, 2015,
|
DOI |
10.1007/s12275-015-5308-9
|
Key Words |
symbiotic nitrogen fixation, oxidative stress, desiccation,
soybean, ECF sigma factor, CarQ |
Abstract |
As a nitrogen-fixing bacterium, Bradyrhizobium japonicum
can establish a symbiotic relationship with the soybean plant
(Glycine max). To be a successful symbiont, B. japonicum
must deal with plant defense responses, such as an oxidative
burst. Our previous functional genomics study showed that
carQ (bll1028) encoding extracytoplasmic function (ECF)
sigma factor was highly expressed (107.8-fold induction)
under oxidative stress. Little is known about the underlying
mechanisms of how CarQ responds to oxidative stress. In
this study, a carQ knock-out mutant was constructed using
site-specific mutagenesis to identify the role of carQ in the
oxidative response of B. japonicum. The carQ mutant showed
a longer generation time than the wild type and exhibited
significantly decreased survival at 10 mM H2O2 for 10 min
of exposure. Surprisingly, there was no significant difference
in expression of oxidative stress-responsive genes such as
katG and sod between the wild type and carQ mutant. The
mutant also showed a significant increase in susceptibility to
H2O2 compared to the wild type in the zone inhibition assay.
Nodulation phenotypes of the carQ mutant were distinguishable
compared to those of the wild type, including lower
numbers of nodules, decreased nodule dry weight, decreased
plant dry weight, and a lower nitrogen fixation capability.
Moreover, desiccation of mutant cells also resulted in significantly
lower percent of survival in both early (after 4 h) and
late (after 24 h) desiccation periods. Taken together, this
information will provide an insight into the role of the ECF
sigma factor in B. japonicum to deal with a plant-derived
oxidative burst. |