Differential expression of two related, low-temperature-induced genes in Arabidopsis thaliana (L.) Heynh.

Plant cold acclimation is correlated to expression of low-temperature-induced (lti) genes. By using a previously characterized lti cDNA clone as a probe we isolated a genomic fragment that carried two closely located lti genes of Arabidopsis thaliana. The genes were structurally related with the coding regions interrupted by three similarly located short introns and were transcribed in the same direction. The nucleotide sequences of the two genes, lti78 and lti65, predict novel hydrophilic polypeptides with molecular weights of 77,856 and 64,510, respectively, lti78 corresponding to the cDNA probe. Of the 710 amino acids of LTI78 and 600 amino acids of LTI65, 346 amino acids were identical between the polypeptides, which suggests that the genes may have a common origin. Both lti78 and lti65 were induced by low temperature, exogenous abscisic acid (ABA) and drought, but the responsiveness of the genes to these stimuli was markedly different. Both the levels and the temporal pattern of expression differed between the genes. Expression of lti78 was mainly responsive to low temperature, that of lti65 to drought and ABA. In contrast to the induction of lti78, which follows separate signal pathways during low-temperature, ABA and drought treatment, the drought induction of lti65 is ABA-dependent and the low-temperature induction appears to be coupled to the ABA biosynthetic pathway. This differential expression of two related genes may indicate that they have somewhat different roles in the stress response.