Molecular Cloning and Expression of cor (Cold-Regulated) Genes in Arabidopsis thaliana

We have previously shown that changes in gene expression occur in Arabidopsis thaliana. L. (Heyn) during cold acclimation (SJ Gilmour, RK Hajela, MF Thomashow [1988] Plant Physiol 87: 745-750). Here we report the isolation of cDNA clones of four cold-regulated (cor) genes from Arabidopsis and examine their expression in response to low temperature, abscisic acid (ABA), water stress, and heat shock. The results of Northern analysis indicated that the transcript levels for the four cor genes, represented by clones pHH7.2, pHH28, pHH29, and pHH67, increased markedly between 1 and 4 hours of cold treatment, reached a maximum at about 8 to 12 hours, and remained at elevated levels for as long as the plants were kept in the cold (up to 2 weeks). Returning cold acclimated plants to control temperature resulted in the levels of the cor transcripts falling rapidly to those found in nonacclimated plants; this occurred within 4 hours for the transcripts represented by pHH7.2 and pHH28, and 8 hours for those represented by pHH29 and pHH67. Nuclear run-on transcription assays indicated that the temperature-regulated expression of the cor genes represented by pHH7.2, pHH28, and pHH29 was controlled primarily at the posttranscriptional level while the cor gene represented by pHH67 was regulated largely at the transcriptional level. Northern analysis also indicated that the levels of cor gene transcripts increased in response to both ABA application and water stress, but not to heat shock. The possible significance of cor genes being regulated by both low temperature and water stress is discussed.