title: Direct interaction of a divergent CaM isoform and the transcription factor, MYB2, enhances salt tolerance in arabidopsis.
abstract: Calmodulin (CaM), a ubiquitous calcium-binding protein, regulates diverse cellular functions by modulating the activity of a variety of enzymes and proteins. Plants express numerous CaM isoforms that exhibit differential activation and/or inhibition of CaM-dependent enzymes in vitro. However, the specific biological functions of plant CaM are not well known. In this study, we isolated a cDNA encoding a CaM binding transcription factor, MYB2, that regulates the expression of salt- and dehydration-responsive genes in Arabidopsis. This was achieved using a salt-inducible CaM isoform (GmCaM4) as a probe from a salt-treated Arabidopsis expression library. Using domain mapping, we identified a Ca2+-dependent CaM binding domain in MYB2. The specific binding of CaM to CaM binding domain was confirmed by site-directed mutagenesis, a gel mobility shift assay, split ubiquitin assay, and a competition assay using a Ca2+/CaM-dependent enzyme. Interestingly, the specific CaM isoform GmCaM4 enhances the DNA binding activity of AtMYB2, whereas this was inhibited by a closely related CaM isoform (GmCaM1). Overexpression of Gm-CaM4 in Arabidopsis up-regulates the transcription rate of AtMYB2-regulated genes, including the proline-synthesizing enzyme P5CS1 (Delta1-pyrroline-5-carboxylate synthetase-1), which confers salt tolerance by facilitating proline accumulation. Therefore, we suggest that a specific CaM isoform mediates salt-induced Ca2+ signaling through the activation of an MYB transcriptional activator, thereby resulting in salt tolerance in plants.
authors.affiliation: Division of Applied Life Science (BK21 Program), Plant Molecular Biology and Biotechnology Research Center, and Environmental Biotechnology National Core Research Center, Gyeongsang National University, Jinju 660-701, Korea.
authors.forename: Jae Hyuk
authors.initials: JH
authors.lastname: Yoo
authors.forename: Chan Young
authors.initials: CY
authors.lastname: Park
authors.forename: Jong Cheol
authors.initials: JC
authors.lastname: Kim
authors.forename: Won Do
authors.initials: WD
authors.lastname: Heo
authors.forename: Mi Sun
authors.initials: MS
authors.lastname: Cheong
authors.forename: Hyeong Cheol
authors.initials: HC
authors.lastname: Park
authors.forename: Min Chul
authors.initials: MC
authors.lastname: Kim
authors.forename: Byeong Cheol
authors.initials: BC
authors.lastname: Moon
authors.forename: Man Soo
authors.initials: MS
authors.lastname: Choi
authors.forename: Yun Hwan
authors.initials: YH
authors.lastname: Kang
authors.forename: Ju Huck
authors.initials: JH
authors.lastname: Lee
authors.forename: Ho Soo
authors.initials: HS
authors.lastname: Kim
authors.forename: Sang Min
authors.initials: SM
authors.lastname: Lee
authors.forename: Hae Won
authors.initials: HW
authors.lastname: Yoon
authors.forename: Chae Oh
authors.initials: CO
authors.lastname: Lim
authors.forename: Dae-Jin
authors.initials: DJ
authors.lastname: Yun
authors.forename: Sang Yeol
authors.initials: SY
authors.lastname: Lee
authors.forename: Woo Sik
authors.initials: WS
authors.lastname: Chung
authors.forename: Moo Je
authors.initials: MJ
authors.lastname: Cho
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D020013:Calcium Signaling / Q000502:physiology; D002147:Calmodulin / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D018076:DNA, Complementary; D018506:Gene Expression Regulation, Plant / Q000502:physiology; D007536:Isomerism; D016297:Mutagenesis, Site-Directed; D030821:Plants, Genetically Modified; D011392:Proline / Q000378:metabolism; D012492:Salts / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin; D015003:Yeasts
chemical_list: D029681:Arabidopsis Proteins; D002147:Calmodulin; D018076:DNA, Complementary; C104175:MYB2 protein, Arabidopsis; D012492:Salts; D015534:Trans-Activators; D025801:Ubiquitin; D011392:Proline