A Semidwarf Phenotype of Barley uzu Results from a Nucleotide Substitution in the Gene Encoding a Putative Brassinosteroid Receptor

Abstract

Brassinosteroids (BRs) play important roles throughout plant growth and development. Despite the importance of clarifying the mechanism of BR-related growth regulation in cereal crops, BR-related cereal mutants have been identified only in rice (Oryza sativa). We previously found that semidwarf barley (Hordeum vulgare) accessions carrying the "uzu" gene, called "uzu" barley in Japan, are non-responding for brassinolide (BL). We then performed chemical and molecular analyses to clarify the mechanisms of uzu dwarfism using isogenic line pairs of uzu gene. The response of the uzu line to BL was significantly lower than that of its corresponding normal line. Measurement of BRs showed that the uzu line accumulates BRs, similar to known BR-insensitive mutants. The marker synteny of rice and barley chromosomes suggests that the uzu gene may be homologous to rice D61, a rice homolog of Arabidopsis BR-insensitive 1 (BRI1), encoding a BR-receptor protein.A barley homolog of BRI1, HvBRI1, was isolated by using degenerate primers. A comparison of HvBRI1 sequences in uzu and normal barley varieties showed that the uzu phenotype is correlated with a single nucleotide substitution. This substitution results in an amino acid change at a highly conserved residue in the kinase domain of the BR-receptor protein.These results may indicate that uzu dwarfism is caused by the missense mutation in HvBRI1. The uzu gene is being introduced into all hull-less barley cultivars in Japan as an effective dwarf gene for practical use, and this is the first report about an agronomically important mutation related to BRs.Brassinolide (BL) is a firstly identified plant steroid hormone, isolated from rape (Brassica napus) pollen (Grove et al., 1979). Diverse plant species have been found to contain BL and a variety of structural analogs, called brassinosteroids (BRs). With their characteristic physiological effect on plant growth and development, BRs should be included as essential plant hormones, along with GAs, auxins, cytokinins (CKs), abscisic acid (ABA), and ethylene. The effect of BRs on germination, elongation growth, flowering, and sex expressions of plants have been reported, and various application techniques have been tested in the greenhouse and in the field (Yokota, 1999). BR applications have often increased grain and vegetable yields. Plants treated with BRs also acquired resistance to or tolerance against such stresses as cold, drought, salt, disease, and herbicide. In field tests, however, BR effects were unstable and not replicable. The biological activity of these BRs disappeared rapidly due to deactivation and was influenced by environmental conditions (Kamuro and Takatsuto, 1999).In addition to studies on agricultural applications of BRs, BR physiology has also been studied (Yokota, 1997; Altmann, 1999; Bishop and Yokota, 2001). After many BR-deficient and -insensitive mutants were identified in Arabidopsis, BR biosynthesis and signaling have been rapidly clarified. BR biosynthesis mutants such as deetiolated 2 (det2; Chory et...

Induced Variations in Brassinosteroid Genes Define Barley Height and Sturdiness, and Expand the Green Revolution Genetic Toolkit

“…Five of eight mutants induced in 'Steptoe' carried a 4-bp and a 1-bp deletion in the 39 untranslated region and two of four mutants induced in 'Akashinriki'-derived lines carried the same deletions plus three nucleotide substitutions that caused two nonsynonymous changes of amino acid residues (Ala-79 to Phe and Leu-1028 to Val) in the BRI1 N-and C-terminal domains, respectively (AkashinrikiII-allele; Chono et al, 2003). None of those haplotypes displayed an obvious brassinosteroid phenotype (Supplemental Data Set S1), which suggests that they are not deficient in HvBRI1.…”

Brassinosteroids and Rice Architecture

“…Very recently, Chono et al 15) reported that a semi-dwarf gene in barley, uzu, encodes a putative BR receptor that is highly homologous to Arabidopsis AtBRI1 and rice OsBRI1. They found that this semi-dwarf barley cultivar, called uzu barley in Japanese, is less responsive to brassinolide and has a high accumulation of BRs.…”

Genetic Dissection of Barley Morphology and Development

“…To explore the feasibility of mutant gene identification using the SNP mapping data and synteny models, we analyzed five NILs where the identity of the mutant locus is known: BW069 and BW880 lines containing the THIRD OUTER GLUME (HvTRD1) gene on chromosome 1H (Whipple et al, 2010), BW898 containing HvVRS1 (Komatsuda et al, 2007) on 2H, BW885 containing HvUZU (Chono et al, 2003) on 3H, and two loci on chromosome 7H, namely BW638 containing the HvNUD1 gene (Taketa et al, 2008) and BW905 containing HvWAXY (Rohde et al, 1988). Based on the assumption that synteny is conserved with rice and that major structural rearrangements are absent, we estimated the number of genes contained within the introgressed segments.…”

“…Barley mutants have been used to isolate or validate genes such as nitrate reductase (Somers et al, 1983), key genes in the anthocyanin pathway (von Wettstein, 2007), a gene responsible for the floral bract phenotype HOODED (Muller et al, 1995), the row-type gene SIX-ROWED SPIKE1 (VRS1; Komatsuda et al, 2007), the hull adhesion gene NAKED CARYOPSIS (NUD; Taketa et al, 2008), plant height genes UZU DWARF (UZU; Chono et al, 2003) and SLENDER1 (Chandler et al, 2002), several endosperm development genes (Felker et al, 1983;Morell et al, 2003;Rö der et al, 2006;Clarke et al, 2008), and two disease lesion mimic mutations NECROTIC1 (Rostoks et al, 2006) and NECROTIC.S1 (Zhang et al, 2009) among others. However, despite these individual achievements, with few exceptions (Pozzi et al, 2003;Rossini et al, 2006), the barley mutant resources have not yet been systematically explored using the tools of modern genetics.…”