New Cold- and Drought-Regulated Gene from Medicago sativa

Plants are known to differ in their ability to withstand freezing temperatures, but the molecular/genetic basis of this differential freezing tolerance is unclear. Exposure of plants to low, nonfreezing temperatures (cold acclimation) increases their tolerance to subsequent freezing (see recent review by Guy, 1990). Significant biochemical modifications occur during cold acclimation of plants, including changes in gene expression (Thomashow, 1990). Three cold acclimation-specific cDNAs (Mohapatra et al., 1989) and one cDNA responsive to environmental stress (cold and drought) and ABA (Mohapatra et al., 1988) have previously been isolated from alfalfa (Medicago sativa L. cv Apica). DNA sequence determination of four alfalfa cDNAs that were shown to be responsive to environmental stresses (low temperature and drought) and ABA indicated that they are part of a family of genes encoding Gly-rich proteins containing many repeated peptide motifs (Lu0 et al., 1991, 1992). We report here the isolation of a new full-length cDNA clone (MsaciA) that is cold and drought regulated in alfalfa. Plants of the cold-tolerant alfalfa were grown at 21OC for 5 weeks and cold acclimated for 2 weeks at 2OC. A XgtlO library was constructed with mRNA isolated from cold-acclimated crowns. The cDNA of a cold-inducible transcript was isolated by differential hybridization using single-strand cDNA synthesized from cold-acclimated and nonacclimated crowns. The nucleotide sequence of the full-length cDNA and the deduced amino acid sequence of MsaciA have been determined (Table I). MsaciA encodes a putative Gly-rich protein (38%), which contains many repeated motifs. This putative protein shares homology in the range of 68 to 88% (amino acid identity) with the previously isolated environmental stressand ABA-regulated putative proteins from alfalfa (Lu0 et al., 1991, 1992) and, thus, represents a new member of this gene family.