Genes Encoding Glycine-Rich Arabidopsis thaliana Proteins with RNA-Binding Motifs Are Influenced by Cold Treatment and an Endogenous Circadian Rhythm

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Abstract
We have characterized the expression of two members of a class of Arabidopsis thaliana glycine-rich, putative RNA-binding proteins that we denote Ccr1 and Ccr2. Southern blot analysis indicates that Ccr1 and Ccr2 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 plants, with maximal accumulation at 6:00 PM and minimal accumulation at 10:00 AM. The level of CCR1 protein, however, remained relatively constant throughout the cycle. The transcript accumulation patterns of the Ccr1 and Ccr2 genes differed considerably from conditions that affect the expression of similar genes from maize, sorghum, and carrot. Levels 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 in abscisic acid-treated plants. Ccr1 transcript levels decreased in response to drought, whereas Ccr2 transcript levels increased under the same conditions. Based on the presence of additional Ccr transcripts in dark-grown plants, we propose that Ccr transcripts may be subjected to a light- or dark-mediated regulation.