title: Ubiquitin ligase EL5 maintains the viability of root meristems by influencing cytokinin-mediated nitrogen effects in rice.
abstract: Root formation is dependent on meristematic activity and is influenced by nitrogen supply. We have previously shown that ubiquitin ligase, EL5, in rice (Oryza sativa) is involved in the maintenance of root meristematic viability. When mutant EL5 protein is overexpressed to dominantly inhibit the endogenous EL5 function in rice, primordial and meristematic necrosis ia observed. Here, we analysed the cause of root cell death in transgenic rice plants (mEL5) overexpressing EL5V162A, which encodes a partly inactive ubiquitin ligase. The mEL5 mutants showed increased sensitivity to nitrogen that was reflected in the inhibition of root formation. Treatment of mEL5 with nitrate or nitrite caused meristematic cell death accompanied by browning. Transcriptome profiling of whole roots exhibited overlaps between nitrite-responsive genes in non-transgenic (NT) rice plants and genes with altered basal expression levels in mEL5. Phytohormone profiling of whole roots revealed that nitrite treatment increased cytokinin levels, but mEL5 constitutively contained more cytokinin than NT plants and showed increased sensitivity to exogenous cytokinin. More superoxide was detected in mEL5 roots after treatment with nitrite or cytokinin, and treatment with an inhibitor of superoxide production prevented mEL5 roots from both nitrite- and cytokinin-induced meristematic cell death. These results indicate a nitrogen-triggered pathway that leads to changes in root formation through the production of cytokinin and superoxide, on which EL5 acts to prevent meristematic cell death.
authors.affiliation: Genetically Modified Organism Research Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Mochizuki
authors.affiliation: Growth Regulation Research Group, RIKEN Plant Science Center, Suehiro-cho 1-7-22, Tsurumi, Yokohama, Kanagawa, 230-0045 Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Jikumaru
authors.affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan.
authors.forename: Hidemitsu
authors.initials: H
authors.lastname: Nakamura
authors.affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan.
authors.forename: Hanae
authors.initials: H
authors.lastname: Koiwai
authors.affiliation: National Institute of Livestock and Grassland Science, Ikenodai 2, Tsukuba, Ibaraki, 305-0901 Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Sasaki
authors.affiliation: Growth Regulation Research Group, RIKEN Plant Science Center, Suehiro-cho 1-7-22, Tsurumi, Yokohama, Kanagawa, 230-0045 Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamiya
authors.affiliation: Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ichikawa
authors.affiliation: Genetically Modified Organism Research Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Minami
authors.affiliation: Genetically Modified Organism Research Center, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan Growth Regulation Research Group, RIKEN Plant Science Center, Suehiro-cho 1-7-22, Tsurumi, Yokohama, Kanagawa, 230-0045 Japan Division of Plant Sciences, National Institute of Agrobiological Sciences, Kannondai 2-1-2, Tsukuba, Ibaraki, 305-8602 Japan National Institute of Livestock and Grassland Science, Ikenodai 2, Tsukuba, Ibaraki, 305-0901 Japan ynishi@affrc.go.jp.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nishizawa
mesh_terms: D002470:Cell Survival; D003583:Cytokinins / Q000378:metabolism*; D018519:Meristem / Q000166:cytology / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000166:cytology / Q000201:enzymology / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D003583:Cytokinins; D010940:Plant Proteins; D044767:Ubiquitin-Protein Ligases; D009584:Nitrogen
keywords: Cytokinin; nitrogen; reactive oxygen species; rice; root cell death; ubiquitin ligase.