Analysis of early-flowering genes at barley chromosome 2H expands the repertoire of mutant alleles at the Mat-c locus.

KEY MESSAGE: Analyses of barley mat-c loss of function mutants reveal deletions, splice-site mutations and nonsynonymous substitutions in a key gene regulating early flowering. Optimal timing of flowering is critical for reproductive success and crop yield improvement. Several major quantitative trait loci for flowering time variation have been identified in barley. In the present study, we analyzed two near-isogenic lines, BW507 and BW508, which were reported to carry two independent early-flowering mutant loci, mat-b.7 and mat-c.19, respectively. Both introgression segments are co-localized in the pericentromeric region of chromosome 2H. We mapped the mutation in BW507 to a 31 Mbp interval on chromosome 2HL and concluded that BW507 has a deletion of Mat-c, which is an ortholog of Antirrhinum majus CENTRORADIALIS (AmCEN) and Arabidopsis thaliana TERMINAL FLOWER1 (AtTFL1). Contrary to previous reports, our data showed that both BW507 and BW508 are Mat-c deficient and none of them are mat-b.7 derived. This work complements previous studies by identifying the uncharacterized mat-c.19 mutant and seven additional mat-c mutants. Moreover, we explored the X-ray structure of AtTFL1 for prediction of the functional effects of nonsynonymous substitutions caused by mutations in Mat-c.

Induced variations in brassinosteroid genes define barley height and sturdiness, and expand the green revolution genetic toolkit.

Reduced plant height and culm robustness are quantitative characteristics important for assuring cereal crop yield and quality under adverse weather conditions. A very limited number of short-culm mutant alleles were introduced into commercial crop cultivars during the Green Revolution. We identified phenotypic traits, including sturdy culm, specific for deficiencies in brassinosteroid biosynthesis and signaling in semidwarf mutants of barley (Hordeum vulgare). This set of characteristic traits was explored to perform a phenotypic screen of near-isogenic short-culm mutant lines from the brachytic, breviaristatum, dense spike, erectoides, semibrachytic, semidwarf, and slender dwarf mutant groups. In silico mapping of brassinosteroid-related genes in the barley genome in combination with sequencing of barley mutant lines assigned more than 20 historic mutants to three brassinosteroid-biosynthesis genes (BRASSINOSTEROID-6-OXIDASE, CONSTITUTIVE PHOTOMORPHOGENIC DWARF, and DIMINUTO) and one brassinosteroid-signaling gene (BRASSINOSTEROID-INSENSITIVE1 [HvBRI1]). Analyses of F2 and M2 populations, allelic crosses, and modeling of nonsynonymous amino acid exchanges in protein crystal structures gave a further understanding of the control of barley plant architecture and sturdiness by brassinosteroid-related genes. Alternatives to the widely used but highly temperature-sensitive uzu1.a allele of HvBRI1 represent potential genetic building blocks for breeding strategies with sturdy and climate-tolerant barley cultivars.

Induced mutations in circadian clock regulator Mat-a facilitated short-season adaptation and range extension in cultivated barley.

Time to flowering has an important impact on yield and has been a key trait in the domestication of crop plants and the spread of agriculture. In 1961, the cultivar Mari (mat-a.8) was the very first induced early barley (Hordeum vulgare L.) mutant to be released into commercial production. Mari extended the range of two-row spring barley cultivation as a result of its photoperiod insensitivity. Since its release, Mari or its derivatives have been used extensively across the world to facilitate short-season adaptation and further geographic range extension. By exploiting an extended historical collection of early-flowering mutants of barley, we identified Praematurum-a (Mat-a), the gene responsible for this key adaptive phenotype, as a homolog of the Arabidopsis thaliana circadian clock regulator Early Flowering 3 (Elf3). We characterized 87 induced mat-a mutant lines and identified >20 different mat-a alleles that had clear mutations leading to a defective putative ELF3 protein. Expression analysis of HvElf3 and Gigantea in mutant and wild-type plants demonstrated that mat-a mutations disturb the flowering pathway, leading to the early phenotype. Alleles of Mat-a therefore have important and demonstrated breeding value in barley but probably also in many other day-length-sensitive crop plants, where they may tune adaptation to different geographic regions and climatic conditions, a critical issue in times of global warming.