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

Abstract

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 mata 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 daylength-sensitive crop plants, where they may tune adaptation to different geographic regions and climatic conditions, a critical issue in times of global warming.earliness | food security | timing of flowering | molecular breeding | synteny

EARLY FLOWERING3 Redundancy Fine-Tunes Photoperiod Sensitivity

“…It also suggests that the simple duplication of the ELF3 gene may have provided a mechanism for achieving a partial loss of photoperiod responsiveness and an optimal compromise between generation of sufficient vegetative biomass to support yield and early completion of the life cycle in short season environments. However, it is also notable that ELF3 mutations provide adaptation in diploid cereals such as barley and einkorn wheat (Faure et al, 2012;Zakhrabekova et al, 2012;Alvarez et al, 2016) where ELF3 is single copy. This suggests that there could be another component to the adaptive advantage of elf3 mutations over other EC mutants, which could reflect unique roles of ELF3 that are conserved in these different crop groups.…”

“…Interestingly, in both crop groups, mutations in ELF3 genes have been shown to contribute to the expansion in range of species through alteration of photoperiod responsiveness and the associated impact on yield (Faure et al, 2012;Matsubara et al, 2012;Weller et al, 2012;Zakhrabekova et al, 2012;Alvarez et al, 2016;Lu et al, 2017). In crop species, a role for ELF4 function has been clearly established only in the legume species pea (Pisum sativum; Liew et al, 2009), but mutations in LUX orthologs have also been shown to cause early flowering and impaired photoperiod response in pea and in the cereals einkorn wheat (Triticum aestivum) and barley (Hordeum vulgare; Mizuno et al, 2012;Campoli et al, 2013;Liew et al, 2014), suggesting that the EC genes are likely to be intimately linked to the photoperiod response mechanism in both crop groups.…”

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

“…In the first case, the mutants were induced by identical chemical treatment (brh3.g, brh3.h, and brh3.i), in the second case by different treatments (ari-o.40, ari-o.43, and ari-o.143). In each case, the mutants were induced in the same mutagenesis program, and thus we cannot exclude a mix-up of mutant accessions after the mutagenic treatment as it was suggested earlier for alleles of barley loci praematurum-a and third outer glume1 (Houston et al, 2012;Zakhrabekova et al, 2012). Two other cases, however, strongly point toward an independent ancestry of identical mutations.…”

An overview of barley breeding and variety trials in Iceland in 1987-2014

“…In 1960, the Swedish cultivar 'Mari' was released (Gustafsson et al 1971, Lundqvist 2008, produced by induced mutagenesis from the cultivar 'Bonus'. 'Mari' carries a deletion in the circadian clock regulator Mat-a gene, making it day length neutral, which results in an early flowering phenotype (Gustafsson et al 1971, Zakhrabekova et al 2012. In addition, 'Mari' has a strong straw, making it resistant to lodging (Gustafsson et al 1971, Zakhrabekova et al 2012.…”

“…'Mari' carries a deletion in the circadian clock regulator Mat-a gene, making it day length neutral, which results in an early flowering phenotype (Gustafsson et al 1971, Zakhrabekova et al 2012. In addition, 'Mari' has a strong straw, making it resistant to lodging (Gustafsson et al 1971, Zakhrabekova et al 2012. The cultivar was grown in Iceland up until the 1980s with little success but has been used in crosses in the Icelandic breeding program.…”