Differential expression of potato calmodulin genes by cold, heat and salt stress

Calmodulin (CaM) is a protein modulated by calcium, an important component of signal transduction of plant response to external stimuli. Three different CaM cDNAs were isolated from a Solanum commersonii library by screening with a RT-PCR fragment amplified from a conserved region of the S. tuberosum CaM1 gene. The three cDNAs (ScCaM1, ScCaM3 and ScCaM5), sharing 85% identity inside the coding region, have a predicted amino acid sequence of 149 residues, highly homologous to other known plant calmodulins (90% identity). The 3'-untranslated regions (UTR) are highly divergent (only 47% homology) and were used as probes to monitor changes in gene expression in potato cells exposed to temperature stress (cold and heat) and NaCl treatment. Transcripts corresponding to ScCaM1 and ScCaM5 were rapidly induced in response to cold, heat and salt stress. However, when the 3' UTR region of each gene was used as probe, differences in the kinetics of induction and the amount of transcripts were revealed. The expression of ScCaM3 genes was only induced in potato leaves after cold treatment but not in the stress condition tested on cells culture. The same stress treatments applied to potato cells pre-exposed to gradual osmotic stress did not affect the steady-state level of CaM mRNAs, suggesting that one or more components involved in the perception and intracellular transduction of temperature stress signal might have been altered under persistent osmotic stress.