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Moving on up: auxin-induced K+ channel expression regulates gravitropism

2000; Elsevier BV; Volume: 5; Issue: 3 Linguagem: Inglês

10.1016/s1360-1385(00)01557-0

1878-4372

Malcolm J. Bennett, Jeremy A. Roberts, Klaus Palme,

14-3-3 protein interactions

Plant growth responses, such as gravitropism, have fascinated generations of scientists since the pioneering work of Julius von Sachs and Charles Darwin more than a century ago 1 Darwin, C. (1880) The Power of Movements in Plants, John Murray, London, UK Google Scholar . More recently, gravitropic research has benefited significantly from the application of Arabidopsis genetics, and this strategy has led to the isolation of several key components of the gravitropic signal transduction pathway (recently reviewed in 2 Rosen E. et al. Root gravitropism: a complex response to a simple stimulus?. Trends Plant Sci. 1999; 4: 407-412 Abstract Full Text Full Text PDF PubMed Scopus (63) Google Scholar ). For example, mutations within genes encoding the putative auxin influx and efflux carrier components AUX1 and AGR1 (also known as AtPIN2 and EIR1) confer an agravitropic phenotype 3 Marchant A. et al. AUX 1 regulates root gravitropism in Arabidopsis by facilitating auxin uptake within root apical tissues. EMBO J. 1999; 18: 2066-2073 Crossref PubMed Scopus (468) Google Scholar , 4 Luschnig C. et al. EIR1, a root-specific protein involved in auxin transport, is required for gravitropism in Arabidopsis thaliana. Genes Dev. 1998; 12: 2175-2187 Crossref PubMed Scopus (666) Google Scholar , 5 Müller A. et al. AtPIN2 defines a locus of Arabidopsis for root gravitropism control. EMBO J. 1998; 17: 6903-6911 Crossref PubMed Scopus (688) Google Scholar , 6 Chen R. et al. The Arabidopsis thaliana AGRAVITROPIC1 gene encodes a component of the polar-auxin-transport efflux carrier. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 15112-15117 Crossref PubMed Scopus (377) Google Scholar , 7 Utsuno K. et al. AGR, an Agravitropic locus of Arabidopsis thaliana, encodes a novel membrane-protein family member. Plant Cell Physiol. 1998; 39: 1111-1118 Crossref PubMed Scopus (163) Google Scholar , underlining the importance of auxin transport to gravitropic signal transduction. In spite of these important advances, several key questions remain unanswered. Firstly, does gravitropic bending arise from asymmetric changes in auxin concen- tration and/or asymmetric changes in tissue auxin sensitivity 8 Li Y. et al. An auxin-responsive promoter is differentially induced by auxin gradients during tropisms. Plant Cell. 1991; 3: 1167-1175 Crossref PubMed Google Scholar , 9 Larkin P.J. et al. Transgenic white clover. Studies with the auxin-responsive promoter, GH3, in root gravitropism and lateral root development. Transgenic Res. 1996; 5: 325-335 Crossref PubMed Scopus (82) Google Scholar ? Secondly, what is the nature of the function(s) of the downstream genes that auxin regulates? The recent work by Rainer Hedrich and colleagues 10 Philippar K. et al. Auxin-induced K+ channel expression represents an essential step in coleoptile growth and gravitropism. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 12186-12191 Crossref PubMed Scopus (248) Google Scholar goes some way to providing answers to both these questions.