title: Functional implication of β-carotene hydroxylases in soybean nodulation.
abstract: Legume-Rhizobium spp. symbiosis requires signaling between the symbiotic partners and differential expression of plant genes during nodule development. Previously, we cloned a gene encoding a putative β-carotene hydroxylase (GmBCH1) from soybean (Glycine max) whose expression increased during nodulation with Bradyrhizobium japonicum. In this work, we extended our study to three GmBCHs to examine their possible role(s) in nodule development, as they were additionally identified as nodule specific, along with the completion of the soybean genome. In situ hybridization revealed the expression of three GmBCHs (GmBCH1, GmBCH2, and GmBCH3) in the infected cells of root nodules, and their enzymatic activities were confirmed by functional assays in Escherichia coli. Localization of GmBCHs by transfecting Arabidopsis (Arabidopsis thaliana) protoplasts with green fluorescent protein fusions and by electron microscopic immunogold detection in soybean nodules indicated that GmBCH2 and GmBCH3 were present in plastids, while GmBCH1 appeared to be cytosolic. RNA interference of the GmBCHs severely impaired nitrogen fixation as well as nodule development. Surprisingly, we failed to detect zeaxanthin, a product of GmBCH, or any other carotenoids in nodules. Therefore, we examined the possibility that most of the carotenoids in nodules are converted or cleaved to other compounds. We detected the expression of some carotenoid cleavage dioxygenases (GmCCDs) in wild-type nodules and also a reduced amount of zeaxanthin in GmCCD8-expressing E. coli, suggesting cleavage of the carotenoid. In view of these findings, we propose that carotenoids such as zeaxanthin synthesized in root nodules are cleaved by GmCCDs, and we discuss the possible roles of the carotenoid cleavage products in nodulation.
authors.affiliation: Department of Biological Science , Sookmyung Women's University, Seoul 140-742, Korea.
authors.forename: Yun-Kyoung
authors.initials: YK
authors.lastname: Kim
authors.forename: Sunghan
authors.initials: S
authors.lastname: Kim
authors.forename: Ji-Hyun
authors.initials: JH
authors.lastname: Um
authors.forename: Kyunga
authors.initials: K
authors.lastname: Kim
authors.forename: Sun-Kang
authors.initials: SK
authors.lastname: Choi
authors.forename: Byung-Hun
authors.initials: BH
authors.lastname: Um
authors.forename: Suk-Woo
authors.initials: SW
authors.lastname: Kang
authors.forename: Jee-Woong
authors.initials: JW
authors.lastname: Kim
authors.forename: Shinichi
authors.initials: S
authors.lastname: Takaichi
authors.forename: Seok-Bo
authors.initials: SB
authors.lastname: Song
authors.forename: Choon-Hwan
authors.initials: CH
authors.lastname: Lee
authors.forename: Ho-Seung
authors.initials: HS
authors.lastname: Kim
authors.forename: Ki Woo
authors.initials: KW
authors.lastname: Kim
authors.forename: Kyoung Hee
authors.initials: KH
authors.lastname: Nam
authors.forename: Suk-Ha
authors.initials: SH
authors.lastname: Lee
authors.forename: Yul-Ho
authors.initials: YH
authors.lastname: Kim
authors.forename: Hyang-Mi
authors.initials: HM
authors.lastname: Park
authors.forename: Sun-Hwa
authors.initials: SH
authors.lastname: Ha
authors.forename: Desh Pal S
authors.initials: DP
authors.lastname: Verma
authors.forename: Choong-Ill
authors.initials: CI
authors.lastname: Cheon
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D003600:Cytosol / Q000201:enzymology; D049308:Dioxygenases / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000235:genetics; D010088:Oxidoreductases / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D018087:Plastids / Q000201:enzymology; D011523:Protoplasts / Q000378:metabolism; D034622:RNA Interference; D053204:Root Nodules, Plant / Q000201:enzymology* / Q000235:genetics; D013025:Glycine max / Q000502:physiology*; D024341:Xanthophylls / Q000032:analysis; D065146:Zeaxanthins
chemical_list: D010940:Plant Proteins; D024341:Xanthophylls; D065146:Zeaxanthins; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C097153:zeaxanthin epoxidase; D049308:Dioxygenases; C079232:beta-carotene hydroxylase