GENES ENCODING GLYCINE-RICH ARABIDOPSIS-THALIANA PROTEINS WITH RNA-BINDING MOTIFS ARE INFLUENCED BY COLD TREATMENT AND AN ENDOGENOUS CIRCADIAN-RHYTHM

We have characterized the expression of two members of a class of Arab idopsis thaliana glycine-rich, putative RNA-binding proteins that we d enote Ccr1 and Ccr2. Southern blot analysis indicates that Ccr1 and Cc r2 are members of a small gene family. Both Ccr1 and Ccr2 mRNA levels were influenced by a circadian rhythm that has an unusual phase for pl ants, with maximal accumulation at 6:00 PM and minimal accumulation at 10:00 AM. The level of CCR1 protein, however, remained relatively con stant throughout the cycle. The transcript accumulation patterns of th e Ccr1 and Ccr2 genes differed considerably from conditions that affec t the expression of similar genes from maize, sorghum, and carrot. Lev els of Ccr1 and Ccr2 mRNAs were unchanged in wounded plants, increased at least 4-fold in cold-stressed plants, and decreased 2- to 3-fold i n abscisic acid-treated plants. Ccr1 transcript levers decreased in re sponse to drought, whereas Ccr2 transcript levels increased under the same conditions. Based on the presence of additional Ccr transcripts i n dark-grown plants, we propose that Ccr transcripts may be subjected to a light- or dark-mediated regulation.