Molecular cloning and relationship to freezing tolerance of cold-acclimation-specific genes of alfalfa.

Cold-acclimation-specific (CAS) gene expression has been examined by screening a cDNA library prepared from poly(A)(+) RNA of cold-acclimated seedlings of a freezing-tolerant variety of alfalfa (Medicago falcata cv Anik). Three CAS cDNA clones, pSM784, pSM2201, and pSM2358, representing different sequence species, have been used to investigate the relative abundance and time-course of accumulation of corresponding transcripts. Results obtained show that the expression of these CAS genes is regulated in a coordinated manner most likely at the level of transcription. The expression of genes, as measured by mRNA abundance corresponding to the three CAS cDNA clones, is not stimulated or induced by heat shock, water stress, abscisic acid, or wounding. A positive correlation is observed between the expression of these cloned sequences and the degree of freezing-tolerance in four alfalfa cultivars.