title: Thioredoxin reductase type C (NTRC) orchestrates enhanced thermotolerance to Arabidopsis by its redox-dependent holdase chaperone function.
abstract: Genevestigator analysis has indicated heat shock induction of transcripts for NADPH-thioredoxin reductase, type C (NTRC) in the light. Here we show overexpression of NTRC in Arabidopsis (NTRC°(E)) resulting in enhanced tolerance to heat shock, whereas NTRC knockout mutant plants (ntrc1) exhibit a temperature sensitive phenotype. To investigate the underlying mechanism of this phenotype, we analyzed the protein's biochemical properties and protein structure. NTRC assembles into homopolymeric structures of varying complexity with functions as a disulfide reductase, a foldase chaperone, and as a holdase chaperone. The multiple functions of NTRC are closely correlated with protein structure. Complexes of higher molecular weight (HMW) showed stronger activity as a holdase chaperone, while low molecular weight (LMW) species exhibited weaker holdase chaperone activity but stronger disulfide reductase and foldase chaperone activities. Heat shock converted LMW proteins into HMW complexes. Mutations of the two active site Cys residues of NTRC into Ser (C217/454S-NTRC) led to a complete inactivation of its disulfide reductase and foldase chaperone functions, but conferred only a slight decrease in its holdase chaperone function. The overexpression of the mutated C217/454S-NTRC provided Arabidopsis with a similar degree of thermotolerance compared with that of NTRC°(E) plants. However, after prolonged incubation under heat shock, NTRC°(E) plants tolerated the stress to a higher degree than C217/454S-NTRC°(E) plants. The results suggest that the heat shock-mediated holdase chaperone function of NTRC is responsible for the increased thermotolerance of Arabidopsis and the activity is significantly supported by NADPH.
authors.affiliation: Division of Applied Life Science (BK21 Program) and PMBBRC, Gyeongsang National University, 501 Jinju-daero, Jinju 660-701, Korea.
authors.forename: Ho Byoung
authors.initials: HB
authors.lastname: Chae
authors.forename: Jeong Chan
authors.initials: JC
authors.lastname: Moon
authors.forename: Mi Rim
authors.initials: MR
authors.lastname: Shin
authors.forename: Yong Hun
authors.initials: YH
authors.lastname: Chi
authors.forename: Young Jun
authors.initials: YJ
authors.lastname: Jung
authors.forename: Sun Yong
authors.initials: SY
authors.lastname: Lee
authors.forename: Ganesh M
authors.initials: GM
authors.lastname: Nawkar
authors.forename: Hyun Suk
authors.initials: HS
authors.lastname: Jung
authors.forename: Jae Kyung
authors.initials: JK
authors.lastname: Hyun
authors.forename: Woe Yeon
authors.initials: WY
authors.lastname: Kim
authors.forename: Chang Ho
authors.initials: CH
authors.lastname: Kang
authors.forename: Dae-Jin
authors.initials: DJ
authors.lastname: Yun
authors.forename: Kyun Oh
authors.initials: KO
authors.lastname: Lee
authors.forename: Sang Yeol
authors.initials: SY
authors.lastname: Lee
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D018869:Heat-Shock Response; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D010084:Oxidation-Reduction; D030821:Plants, Genetically Modified; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D013696:Temperature; D013880:Thioredoxin-Disulfide Reductase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D018832:Molecular Chaperones; D009249:NADP; D013880:Thioredoxin-Disulfide Reductase