Enhanced expression of a calcium-dependent protein kinase from the moss Funaria hygrometrica under nutritional starvation

Among the downstream targets of calcium in plants, calcium-dependent protei n kinases (CDPKs) form an interesting class of kinases which are activated by calcium binding. They have been implicated in a diverse array of respons es to hormonal and environmental stimuli. In order to dissect the role of C DPKs in the moss Funaria hygrometrica, a polymerase chain reaction (PCR)-ba sed approach was adopted to clone the gene. Using degenerate PCR primers ag ainst conserved regions of CDPKs, a 900 bp amplicon was obtained from the g enomic DNA of Funaria. Southern hybridization under low stringency conditio ns indicated the presence of several CDPK related sequences in the Funaria genome. This observation is consistent with reports of multigene families o f CDPKs in other plants. The 900 bp fragment was subsequently used to isola te a 22 kb partial genomic clone of the CDPK gene from Funaria. The genomic clone encodes an open reading frame (ORF) of 518 amino acids. Interestingl y, unlike other CDPK genes from plants, the entire 1.5 kb ORF is not interr upted by introns. The deduced amino acid sequence of the Funaria gene shows extensive homology with CDPKs from higher plants, 73% identity with the Fu naria CDPK and 71% identity with CDPK isoform 7 of Arabidopsis. Phylogeneti c analysis revealed that the Funaria CDPK is closer to the CDPKs from highe r plants like strawberry and Arabidopsis as compared to those from lower pl ants such as the liverwort Marchantia, the green alga Chlamydomonas or anot her moss Tortula. Northern analysis shows enhanced expression of the CDPK t ranscript within 24-48 h of starvation for nitrogen, phosphorus or sulphur. So far the only other kinase which is known to be induced by nutrient star vation in plants is the wpk 4 which is a snf-1 related kinase (SnRKs). To o ur knowledge this is the first report that implicates a CDPK in the starvat ion response.