2 HOMOLOGOUS LOW-TEMPERATURE-INDUCIBLE GENES FROM ARABIDOPSIS ENCODE HIGHLY HYDROPHOBIC PROTEINS

We have characterized two related cDNAs (RCI2A and RCI2B) correspondin g to genes from Arabidopsis thaliana, the expression of which is trans iently induced by low, nonfreezing temperatures. RCI2A and RCI2B encod e small (54 amino acids), highly hydrophobic proteins that bear two po tential transmembrane domains. They show similarity to proteins encode d by genes from barley (Hordeum volgare L.) and wheatgrass (Lophophyro m elongatum) that are regulated by different stress conditions. Their high level of sequence homology (78%) and their genomic location in a single restriction fragment suggest that both genes originated as a re sult of a tandem duplication. However, their regulatory sequences have diverged enough to confer on them different expression patterns. Like most of the cold-inducible plant genes characterized, the expression of RCI2A and RCI2B is also promoted by abscisic acid (ABA) and dehydra tion but is not a general response to stress conditions, since it is n ot induced by salt stress or by anaerobiosis. Furthermore, low tempera tures are able to induce RCI2A and RCI2B expression in ABA-deficient a nd -insensitive genetic backgrounds, indicating that both ABA-dependen t and -independent pathways regulate the low-temperature responsivenes s of these two genes.