Cloning and expression of calmodulin genes regulating phytoalexin production in carrot cells

A homology-based cloning strategy yielded four cDNA clones encoding the open reading frame of carrot calmodulin, designated cam-4 and cam-8 from an oligogalacturonide elicitor-treated cell culture and cam-11 and cam-16 from cells exposed to ethylene, respectively. Reverse-transcription polymerase chain reaction analyses revealed that the expression of the cam-4 gene increased transiently when carrot seedlings were treated with oligogalacturonides, although, the cells incubated with fungal mycelial walls or ethylene did not show a significant change in the expression level. In contrast, marked and transient expression was observed for either cam-11 or cam-16 only when carrot cells were treated with ethylene. These results suggest that two classes of stimuli which are capable of triggering phytoalexin production in carrot cells, oligogalacturonides and ethylene, evoke the activation of the Ca2+ cascade in the cells by expressing distinct calmodulin genes to initiate the biosynthesis of the compound.