Molecular characterisation of a calmodulin gene, VcCaM1, that is differentially expressed under aluminium stress in highbush blueberry

Calmodulin (CaM), a small acidic protein, is one of the best characterised Ca(2+) sensors in eukaryotes. This Ca(2+) -regulated protein plays a critical role in decoding and transducing environmental stress signals by activating specific targets. Many environmental stresses elicit changes in intracellular Ca(2+) activity that could initiate adaptive responses under adverse conditions. We report the first molecular cloning and characterisation of a calmodulin gene, VcCaM1 (Vaccinium corymbosum Calmodulin 1), in the woody shrub, highbush blueberry. VcCaM1 was first identified as VCAL19, a gene induced by aluminium stress in V. corymbosum L. A full-length cDNA of VcCaM1 containing a 766-bp open reading frame (ORF) encoding 149 amino acids was cloned from root RNA. The sequence encodes four Ca(2+) -binding motifs (EF-hands) and shows high similarity (99%) with the isoform CaM 201 of Daucus carota. Expression analyses showed that following Al treatment, VcCaM1 message level decreased in roots of Brigitta, an Al-resistant cultivar, and after 48 h, was lower than in Bluegold, an Al-sensitive cultivar. VcCAM1 message also decreased in leaves of both cultivars within 2 h of treatment. Message levels in leaves then increased by 24 h to control levels in Brigitta, but not in Bluegold, but then decreased again by 48 h. In conclusion, VcCaM1 does not appear to be directly involved in Al resistance, but may be involved in improved plant performance under Al toxicity conditions through regulation of Ca(2+) homeostasis and antioxidant systems in leaves.