Characterization of two novel cold-inducible K3 dehydrin genes from alfalfa (Medicago sativa spp. sativa L.).

Dehydrin defines a complex family of intrinsically disordered proteins with potential adaptive value with regard to freeze-induced cell dehydration. Search within an expressed sequence tags library from cDNAs of cold-acclimated crowns of alfalfa (Medicago sativa spp. sativa L.) identified transcripts putatively encoding K3-type dehydrins. Analysis of full-length coding sequences unveiled two highly homologous sequence variants, K3-A and K3-B. An increase in the frequency of genotypes yielding positive genomic amplification of the K3-dehydrin variants in response to selection for superior tolerance to freezing and the induction of their expression at low temperature strongly support a link with cold adaptation. The presence of multiple allelic forms within single genotypes and independent segregation indicate that the two K3 dehydrin variants are encoded by distinct genes located at unlinked loci. The co-inheritance of the K3-A dehydrin with a Y2K4 dehydrin restriction fragment length polymorphism with a demonstrated impact on freezing tolerance suggests the presence of a genome domain where these functionally related genes are located. These results provide additional evidence that dehydrin play important roles with regard to tolerance to subfreezing temperatures. They also underscore the value of recurrent selection to help identify variants within a large multigene family in allopolyploid species like alfalfa.