title: Characterization of a Functional Role of the Bradyrhizobium japonicum Isocitrate Lyase in Desiccation Tolerance.
abstract: Bradyrhizobium japonicum is a nitrogen-fixing symbiont of soybean. In previous studies, transcriptomic profiling of B. japonicum USDA110, grown under various environmental conditions, revealed the highly induced gene aceA, encoding isocitrate lyase (ICL). The ICL catalyzes the conversion of isocitrate to succinate and glyoxylate in the glyoxylate bypass of the TCA cycle. Here, we evaluated the functional role of B. japonicum ICL under desiccation-induced stress conditions. We purified AceA (molecular mass = 65 kDa) from B. japonicum USDA110, using a His-tag and Ni-NTA column approach, and confirmed its ICL enzyme activity. The aceA mutant showed higher sensitivity to desiccation stress (27% relative humidity (RH)), compared to the wild type. ICL activity of the wild type strain increased approximately 2.5-fold upon exposure to 27% RH for 24 h. The aceA mutant also showed an increased susceptibility to salt stress. Gene expression analysis of aceA using qRT-PCR revealed a 148-fold induction by desiccation, while other genes involved in the glyoxylate pathway were not differentially expressed in this condition. Transcriptome analyses revealed that stress-related genes, such as chaperones, were upregulated in the wild-type under desiccating conditions, even though fold induction was not dramatic (ca. 1.5-2.5-fold).
authors.affiliation: Department of Biology, University of Texas, Arlington, TX 76019, USA. jeongm@uta.edu.
authors.forename: Jeong-Min
authors.initials: JM
authors.lastname: Jeon
authors.affiliation: Department of Biology, University of Texas, Arlington, TX 76019, USA. hilee@uta.edu.
authors.forename: Hae-In
authors.initials: HI
authors.lastname: Lee
authors.affiliation: Department of Soil, Water & Climate, and The BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA. msugawara@ige.tohoku.ac.jp.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sadowsky
authors.affiliation: Department of Soil, Water & Climate, and The BioTechnology Institute, University of Minnesota, St. Paul, MN 55108, USA. msugawara@ige.tohoku.ac.jp.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Sugawara
authors.affiliation: Department of Biology, University of Texas, Arlington, TX 76019, USA. wschang@uta.edu.|Division of Biotechnology, College of Environmental and Bioresource Sciences, Chonbuk National University, Iksan 570-752, Korea. wschang@uta.edu.
authors.forename: Woo-Suk
authors.initials: WS
authors.lastname: Chang
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D020369:Bradyrhizobium / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D003890:Desiccation; D007522:Isocitrate Lyase / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D007522:Isocitrate Lyase
keywords: Bradyrhizobium japonicum; aceA; desiccation stress; isocitrate lyase (ICL); symbiotic nitrogen fixation