title: A C2H2-type zinc finger protein, SGR5, is involved in early events of gravitropism in Arabidopsis inflorescence stems.
abstract: Plants can sense the direction of gravity and change the growth orientation of their organs. To elucidate the molecular mechanisms of gravity perception and the signal transduction of gravitropism, we have characterized a number of shoot gravitropism (sgr) mutants of Arabidopsis. The sgr5-1 mutant shows reduced gravitropism in the inflorescence stem but its root and hypocotyl have normal gravitropism. SGR5 encodes a zinc finger protein with a coiled-coil motif. The SGR5-GFP fusion protein is localized in the nucleus of Arabidopsis protoplasts, suggesting that SGR5 may act as a transcription factor. Analysis of GUS expression under the control of the SGR5 promoter revealed that SGR5 is mainly expressed in the endodermis, the gravity-sensing tissue in inflorescence stems. Furthermore, the observation that endodermis-specific expression of SGR5 using the SCR promoter in the sgr5-1 mutant restores shoot gravitropism indicates that it could function in the gravity-sensing endodermal cell layer. In contrast to other sgr mutants reported previously, almost all amyloplasts in the endodermal cells of the sgr5-1 mutant sedimented in the direction of gravity. Taken together, our results suggest that SGR5 may be involved in an early event in shoot gravitropism such as gravity perception and/or a signaling process subsequent to amyloplast sedimentation as a putative transcription factor in gravity-perceptive cells.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Takayama 8916-5, Ikoma, Nara 630-0101, Japan.
authors.forename: Miyo T
authors.initials: MT
authors.lastname: Morita
authors.forename: Keitaro
authors.initials: K
authors.lastname: Sakaguchi
authors.forename: Shin-Ichiro
authors.initials: S
authors.lastname: Kiyose
authors.forename: Kensuke
authors.initials: K
authors.lastname: Taira
authors.forename: Takehide
authors.initials: T
authors.lastname: Kato
authors.forename: Moritaka
authors.initials: M
authors.lastname: Nakamura
authors.forename: Masao
authors.initials: M
authors.lastname: Tasaka
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000254:growth & development* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D035264:Flowers / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D018522:Gravitropism / Q000502:physiology*; D008969:Molecular Sequence Data; D010802:Phylogeny; D018547:Plant Stems / Q000254:growth & development* / Q000378:metabolism*; D013997:Time Factors; D016335:Zinc Fingers
chemical_list: D029681:Arabidopsis Proteins; D002352:Carrier Proteins; C517428:SGR5 protein, Arabidopsis