An Arabidopsis Brassinosteroid-Dependent Mutant Is Blocked in Cell Elongation

Abstract

Cell elongation is a developmental process that is regulated by light and phytohormones and is of critical importance for plant growth. Mutants defective in their response to light and various hormones are often dwarfs. The dwarfed phenotype results because of a failure in normal cell elongation. Little is known, however, about the basis of dwarfism as a common element in these diverse signaling pathways and the nature of the cellular functions responsible for cell elongation. Here, we describe an Arabidopsis mutant, dwarf4 (dwf4), whose phenotype can be rescued with exogenously supplied brassinolide. dwf4 mutants display features of light-regulatory mutants, but the dwarfed phenotype is entirely and specifically brassinosteroid dependent; no other hormone can rescue dwf4 to a wild-type phenotype. Therefore, an intact brassinosteroid system is an absolute requirement for cell elongation.

BRL1 and BRL3 are novel brassinosteroid receptors that function in vascular differentiation inArabidopsis

“…bri1 is the only BR-insensitive loss-of-function mutant identified so far by genetic screens (Clouse et al, 1996;Kauschmann et al, 1996;Li and Chory, 1997). Dark-grown bri1 mutants resemble BRdeficient mutants, exhibiting severe dwarfism with dark green epinastic leaves, and reduced apical dominance and fertility (Clouse et al, 1996;Kauschmann et al, 1996;Li et al, 1996;Szekeres et al, 1996;Azpiroz et al, 1998;Choe et al, 1999;Choe et al, 2001;Noguchi et al, 1999).…”

Strigolactone Acts Downstream of Auxin to Regulate Bud Outgrowth in Pea and Arabidopsis

“…Until the isolation and characterization of branching mutants in various species, it was not possible to address these issues. In recent decades, many branching mutants have been isolated that have problems with auxin, cytokinin, or brassinosteroids, for example, and show highly pleiotropic phenotypes typical for these hormones (Lincoln et al, 1990;Azpiroz et al, 1998;Tantikanjana et al, 2001). However, a class of mutants were isolated that displayed a specific increase in bud outgrowth that was not correlated with any known hormonal signal (Beveridge et al, 1996(Beveridge et al, , 1997.…”

The <i>axhs1</i>/<i>dwf4</i> auxin-hypersensitive mutant of <i>Arabidopsis thaliana</i> defines a link for integration of auxin and brassinosteroid mediated root elongation

“…DWF4 is a C-22-α-hydrolase that catalyzes the rate limiting step of BR biosynthesis (Choe et al 1998). Null dwf4 mutations (Azpiroz et al 1998;Nakamoto et al 2006) are infertile and showed a stronger dwarf phenotype compared to that of axhs1, indicating that axhs1 is a weak allele of DWF4. Nakamoto et al (2006) found that inhibition of BR biosynthesis by either a leaky mutation of DWF4 or Brz rescues defects in tropic responses of hypocotyls in the Arabidopsis nph4(arf7) mutant.…”

“…On the other hand, we carried out a complementation test between axhs1 and dwf4-102. Since strong mutant alleles of DWF4 are infertile (Azpiroz et al 1998;Nakamoto et al 2006), heterozygous dwf4-102 was crossed with axhs1. Analysis of the F1 and F2 segregation indicated that axhs1 is allelic to dwf4-102 ( Figure 3F).…”