The barley (Hordeum vulgare L.) dehydrin multigene family: sequences, allele types, chromosome assignments, and expression characteristics of 11 Dhn genes of cv Dicktoo

Dehydrins (LEA D11 proteins) have been identified in both higher and lower plants, and are associated with tolerance to, or response to the onset of, low temperature or dehydration. Several studies have suggested that specifi c alleles of Dhn genes may contribute to a number of phenotypic traits, inc luding the emergence of seedlings in cool or saline soils and the frost tol erance of more-mature plants. However, an incomplete collection of the Dhn multigene family in any system and nucleic acid cross-hybridization between Dhn gene-family members have limited the precision of these studies. We at tempted to overcome these impediments by determining the nucleotide sequenc es of the entire Dhn multigene family in barley and by developing gene-spec ific probes. We identified 11 unique Dicktoo Dhn genes. Seven appear to be alleles of Dhn genes identified previously in other barley cultivars. Anoth er, Dhn9, appears to be orthologous to a Triticum durum Dhn gene. A statist ical analysis of the total collection of genomic clones brings the estimate d size of the barley Dhn gene family to 13. Allelic differences in the prot ein-coding regions appear to result principally from duplications of entire Phi-segments or single amino-acid substitutions, suggesting that polypepti de structural constraints have been a strong force in the evolution of Dhn alleles. Chromosome mapping by PCR with wheat-barley addition lines establi shed the presence of Dhn genes in four barley chromosomes (3H, 4H, 5H, 6H). RT-PCR demonstrated that the Dhn genes are differentially regulated under dehydration, low temperature and ABA treatment, consistent with putative re gulatory elements located upstream of the respective Dhn coding regions. Th is whole-genome, gene-specific study unifies what previously seemed to be d isparate-mapping, expression, and genetic-variation data for Dhn genes in t he Triticeae and other plant systems.