Title: AtMYB61, an R2R3-MYB Transcription Factor Controlling Stomatal Aperture in Arabidopsis thaliana
Abstract: Stomata, dynamic pores found on the surfaces of plant leaves, control water loss from the plant and regulate the uptake of CO2 for photosynthesis [1Hetherington A.M. Woodward F.I. The role of stomata in sensing and driving environmental change.Nature. 2003; 424: 901-908Crossref PubMed Scopus (1332) Google Scholar]. Stomatal aperture is controlled by the two guard cells that surround the stomatal pore [1Hetherington A.M. Woodward F.I. The role of stomata in sensing and driving environmental change.Nature. 2003; 424: 901-908Crossref PubMed Scopus (1332) Google Scholar]. When the two guard cells are fully turgid, the pore gapes open, whereas turgor loss results in stomatal closure. In order to set the most appropriate stomatal aperture for the prevailing environmental conditions, guard cells respond to multiple internal and external signals [2Hetherington A.M. Guard cell signaling.Cell. 2001; 107: 711-714Abstract Full Text Full Text PDF PubMed Scopus (222) Google Scholar]. Although much is known about guard-cell signaling pathways [2Hetherington A.M. Guard cell signaling.Cell. 2001; 107: 711-714Abstract Full Text Full Text PDF PubMed Scopus (222) Google Scholar, 3Assmann S.M. Signal transduction in guard cells.Annu. Rev. Cell Biol. 1993; 9: 345-375Crossref PubMed Scopus (354) Google Scholar, 4Evans N.H. Hetherington A.M. Plant physiology: The ups and downs of guard cell signalling.Curr. Biol. 2001; 11: R92-R94Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar, 5Assmann S.M. Wang X.Q. From milliseconds to millions of years: Guard cells and environmental responses.Curr. Opin. Plant Biol. 2001; 4: 421-428Crossref PubMed Scopus (133) Google Scholar, 6Schroeder J.I. Allen G.J. Hugouvieux V. Kwak J.M. Waner D. Guard cell signal transduction.Annu. Rev. Plant Physiol. Plant Mol. Biol. 2001; 52: 627-658Crossref PubMed Scopus (866) Google Scholar, 7Schroeder J.I. Kwak J.M. Allen G.J. Guard cell abscisic acid signalling and engineering drought hardiness in plants.Nature. 2001; 410: 327-330Crossref PubMed Scopus (568) Google Scholar, 8Fan L.M. Zhao Z. Assmann S.M. Guard cells: A dynamic signaling model.Curr. Opin. Plant Biol. 2004; 7: 537-546Crossref PubMed Scopus (187) Google Scholar, 9Vavasseur A. Raghavendra A.S. Guard cell metabolism and CO2 sensing.New Phytol. 2005; 165: 665-682Crossref PubMed Scopus (150) Google Scholar], rather little is known about how changes in gene expression are involved in the control of stomatal aperture [10Leonhardt N. Kwak J.M. Robert N. Waner D. Leonhardt G. Schroeder J.I. Microarray expression analyses of Arabidopsis guard cells and isolation of a recessive abscisic acid hypersensitive protein phosphatase 2C mutant.Plant Cell. 2004; 16: 596-615Crossref PubMed Scopus (438) Google Scholar]. We show here that AtMYB61 (At1g09540), a gene encoding a member of the Arabidopsis thaliana R2R3-MYB family of transcription factors, is specifically expressed in guard cells in a manner consistent with involvement in the control of stomatal aperture. Gain-of-function and loss-of-function mutant analyses reveal that AtMYB61 expression is both sufficient and necessary to bring about reductions in stomatal aperture with consequent effects on gas exchange. Taken together, our data provide evidence that AtMYB61 encodes the first transcription factor implicated in the closure of stomata.