Transcriptional activation of a maize calcium-dependent protein kinase gene in response to fungal elicitors and infection.

Plants respond to pathogen infection with the activation of the expression of pathogenesis-related genes, a response that involves Ca2+-regulated protein phosphorylation processes. We report here the isolation of a full-length complementary DNA encoding a calcium-dependent protein kinase (CPK) gene from maize. CPK genes occur in maize as members of a multigene family, but only one specific CPK gene, the ZmCPK10 gene here described, is transcriptionally activated in response to both fungal infection and treatment with fungal elicitors. Activation of the ZmCPK10 gene is extremely rapid. ZmCPK10 transcripts could be detected 5 min after elicitation and reached maximum levels at 30 min after treatment. Afterwards, there was a decline in the level of ZmCPK10 transcripts followed by a basal level of accumulation which is maintained over the time period of elicitor treatment. The activation of this kinase is accompanied by an increase in the level of PRms mRNA, the PRms being a pathogenesis-related protein from maize whose expression is induced in maize tissues in response to fungal infection and treatment with fungal elicitors. In situ mRNA hybridization analysis revealed a remarkable cell-type specific pattern of expression of ZmCPK10 during growth and development of the elicitor-treated or fungus-infected seedling. Moreover, the ZmCPK10 gene is expressed only in those specific cell types in which the PRms gene is also expressed. The involvement of ZmCPK10 in the elicitor-induced signal transduction pathway leading to the activation of PRms gene expression is discussed.