title: Poplar GTL1 is a Ca2+/calmodulin-binding transcription factor that functions in plant water use efficiency and drought tolerance.
abstract: Diminishing global fresh water availability has focused research to elucidate mechanisms of water use in poplar, an economically important species. A GT-2 family trihelix transcription factor that is a determinant of water use efficiency (WUE), PtaGTL1 (GT-2 like 1), was identified in Populus tremula × P. alba (clone 717-IB4). Like other GT-2 family members, PtaGTL1 contains both N- and C-terminal trihelix DNA binding domains. PtaGTL1 expression, driven by the Arabidopsis thaliana AtGTL1 promoter, suppressed the higher WUE and drought tolerance phenotypes of an Arabidopsis GTL1 loss-of-function mutation (gtl1-4). Genetic suppression of gtl1-4 was associated with increased stomatal density due to repression of Arabidopsis STOMATAL DENSITY AND DISTRIBUTION1 (AtSDD1), a negative regulator of stomatal development. Electrophoretic mobility shift assays (EMSA) indicated that a PtaGTL1 C-terminal DNA trihelix binding fragment (PtaGTL1-C) interacted with an AtSDD1 promoter fragment containing the GT3 box (GGTAAA), and this GT3 box was necessary for binding. PtaGTL1-C also interacted with a PtaSDD1 promoter fragment via the GT2 box (GGTAAT). PtaSDD1 encodes a protein with 60% primary sequence identity with AtSDD1. In vitro molecular interaction assays were used to determine that Ca(2+)-loaded calmodulin (CaM) binds to PtaGTL1-C, which was predicted to have a CaM-interaction domain in the first helix of the C-terminal trihelix DNA binding domain. These results indicate that, in Arabidopsis and poplar, GTL1 and SDD1 are fundamental components of stomatal lineage. In addition, PtaGTL1 is a Ca(2+)-CaM binding protein, which infers a mechanism by which environmental stimuli can induce Ca(2+) signatures that would modulate stomatal development and regulate plant water use.
authors.affiliation: Department of Horticulture and Landscape Architecture, Center for Plant Environmental Stress Physiology, Purdue University, West Lafayette, Indiana, United States of America.
authors.forename: Hua
authors.initials: H
authors.lastname: Weng
authors.forename: Chan Yul
authors.initials: CY
authors.lastname: Yoo
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Gosney
authors.forename: Paul M
authors.initials: PM
authors.lastname: Hasegawa
authors.forename: Michael V
authors.initials: MV
authors.lastname: Mickelbart
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D002118:Calcium / Q000737:chemistry*; D002147:Calmodulin / Q000737:chemistry*; D002148:Calmodulin-Binding Proteins / Q000235:genetics / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D055864:Droughts; D017343:Genes, Plant / Q000235:genetics*; D008957:Models, Genetic; D009154:Mutation; D010641:Phenotype; D018515:Plant Leaves / Q000235:genetics; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014867:Water / Q000737:chemistry
chemical_list: D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D014867:Water; D002118:Calcium