title: Overexpression of class 1 plant hemoglobin genes enhances symbiotic nitrogen fixation activity between Mesorhizobium loti and Lotus japonicus.
abstract: Plant hemoglobins (Hbs) have been divided into three groups: class 1, class 2, and truncated Hbs. The various physiological functions of class 1 Hb include its role as a modulator of nitric oxide (NO) levels in plants. To gain more insight into the functions of class 1 Hbs, we investigated the physical properties of LjHb1 and AfHb1, class 1 Hbs of a model legume Lotus japonicus and an actinorhizal plant Alnus firma, respectively. Spectrophotometric analysis showed that the recombinant form of the LjHb1 and AfHb1 proteins reacted with NO. The localization of LjHb1 expression was correlated with the site of NO production. Overexpression of LjHb1 and AfHb1 by transformed hairy roots caused changes in symbiosis with rhizobia. The number of nodules formed on hairy roots overexpressing LjHb1 or AfHb1 increased compared with that on untransformed hairy roots. Furthermore, nitrogenase activity as acetylene-reduction activity (ARA) of LjHb1- or AfHb1-overexpressing nodules was higher than that of the vector control nodules. Microscopic observation with a NO-specific fluorescent dye suggested that the NO level in LjHb1- and AfHb1-overexpressing nodules was lower than that of control nodules. Exogenous application of a NO scavenger enhanced ARA in L. japonicus nodules, whereas a NO donor inhibited ARA. These results suggest that the basal level of NO in nodules inhibits nitrogen fixation, and overexpression of class 1 Hbs enhances symbiotic nitrogen fixation activity by removing NO as an inhibitor of nitrogenase.
authors.affiliation: National Institute of Agrobiological Sciences, Tsukuba, Ibaraki 305-8602, Japan.
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Shimoda
authors.forename: Fuyuko
authors.initials: F
authors.lastname: Shimoda-Sasakura
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Kucho
authors.forename: Norihito
authors.initials: N
authors.lastname: Kanamori
authors.forename: Maki
authors.initials: M
authors.lastname: Nagata
authors.forename: Akihiro
authors.initials: A
authors.lastname: Suzuki
authors.forename: Mikiko
authors.initials: M
authors.lastname: Abe
authors.forename: Shiro
authors.initials: S
authors.lastname: Higashi
authors.forename: Toshiki
authors.initials: T
authors.lastname: Uchiumi
mesh_terms: D000114:Acetylene / Q000378:metabolism; D029661:Alnus / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D020561:Alphaproteobacteria / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006454:Hemoglobins / Q000235:genetics / Q000378:metabolism*; D000070116:Lotus / Q000235:genetics* / Q000378:metabolism / Q000382:microbiology; D009569:Nitric Oxide / Q000378:metabolism; D009586:Nitrogen Fixation / Q000235:genetics*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D018749:RNA, Plant / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D053204:Root Nodules, Plant / Q000235:genetics / Q000378:metabolism / Q000382:microbiology; D013559:Symbiosis
chemical_list: D006454:Hemoglobins; D010940:Plant Proteins; D018749:RNA, Plant; D011994:Recombinant Proteins; D009569:Nitric Oxide; D000114:Acetylene