title: Overexpression of the bZIP transcription factor OsbZIP79 suppresses the production of diterpenoid phytoalexin in rice cells.
abstract: Phytoalexins are antimicrobial specialised metabolites that are produced by plants in response to pathogen attack. Momilactones and phytocassanes are major diterpenoid phytoalexins in rice that are synthesised from geranylgeranyl diphosphate that is derived from the methylerythritol phosphate (MEP) pathway. We have previously reported that rice cells overexpressing the basic leucine zipper (bZIP) transcription factor OsTGAP1 exhibit a hyperaccumulation of momilactones and phytocassanes, with hyperinductive expression of momilactone and phytocassane biosynthetic genes and MEP pathway genes, upon response to a chitin oligosaccharide elicitor. For a better understanding of OsTGAP1-mediated regulation of diterpenoid phytoalexin production, we identified OsTGAP1-interacting proteins using yeast two-hybrid screening. Among the OsTGAP1-interacting protein candidates, a TGA factor OsbZIP79 was investigated to verify its physical interaction with OsTGAP1 and involvement in the regulation of phytoalexin production. An in vitro pull-down assay demonstrated that OsTGAP1 and OsbZIP79 exhibited a heterodimeric as well as a homodimeric interaction. A bimolecular fluorescence complementation analysis also showed the interaction between OsTGAP1 and OsbZIP79 in vivo. Intriguingly, whereas OsbZIP79 transactivation activity was observed in a transient reporter assay, the overexpression of OsbZIP79 resulted in suppression of the elicitor-inducible expression of diterpenoid phytoalexin biosynthetic genes, and thus caused a decrease in the accumulation of phytoalexin in rice cells. These results suggest that OsbZIP79 functions as a negative regulator of phytoalexin production triggered by a chitin oligosaccharide elicitor in rice cells, although it remains open under which conditions OsbZIP79 can work with OsTGAP1.
authors.affiliation: Department of Biosciences, Teikyo University, 1-1 Toyosatodai, Utsunomiya, Tochigi 320-8551, Japan; Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Electronic address: miyamoto@nasu.bio.teikyo-u.ac.jp.
authors.forename: Koji
authors.initials: K
authors.lastname: Miyamoto
authors.affiliation: Disease Resistant Crops Research Unit, GMO Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan. Electronic address: ynishi@affrc.go.jp.
authors.forename: Yoko
authors.initials: Y
authors.lastname: Nishizawa
authors.affiliation: Disease Resistant Crops Research Unit, GMO Research Center, National Institute of Agrobiological Sciences, 2-1-2 Kannondai, Tsukuba, Ibaraki 305-8602, Japan. Electronic address: eiminami@affrc.go.jp.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Minami
authors.affiliation: Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Electronic address: anojiri@mail.ecc.u-tokyo.ac.jp.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Nojiri
authors.affiliation: Department of Biosciences, Teikyo University, 1-1 Toyosatodai, Utsunomiya, Tochigi 320-8551, Japan. Electronic address: hyamane@nasu.bio.teikyo-u.ac.jp.
authors.forename: Hisakazu
authors.initials: H
authors.lastname: Yamane
authors.affiliation: Biotechnology Research Center, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan. Electronic address: ukokada@mail.ecc.u-tokyo.ac.jp.
authors.forename: Kazunori
authors.initials: K
authors.lastname: Okada
mesh_terms: D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics* / Q000378:metabolism; D004224:Diterpenes / Q000378:metabolism*; D015870:Gene Expression; D015723:Gene Library; D012275:Oryza / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D011106:Polyisoprenyl Phosphates / Q000378:metabolism; D012717:Sesquiterpenes / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D000094162:Phytoalexins
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D004224:Diterpenes; D010940:Plant Proteins; D011106:Polyisoprenyl Phosphates; D012717:Sesquiterpenes; C002963:geranylgeranyl pyrophosphate; D000094162:Phytoalexins
keywords: Metabolic gene cluster; Phytoalexin; Rice; TGA factor; bZIP transcription factor