Search

* Arabidopsis cngc2 plants are hypersensitive to external calcium and exhibit reduced plant size and fertility, especially when they are treated with elevated but physiologically relevant levels of calcium. This report focuses on the role of cyclic nucleotide-gated channel 2 (CNGC2) in plant fertility. * To determine the cause of the reduced fertility, we investigated the flower structure and growth potential of both male and female reproductive organs in cngc2 plants grown in high-calcium conditions. * cngc2 mutants had short stamens that may limit pollen deposition and pistils that were not conducive to pollen tube growth. * Our data indicate that sporophytic, but not gametophytic, defects are the main cause of the observed reduction in seed yield in cngc2 plants, and suggest that correct cyclic nucleotide and calcium signaling are important for cell elongation and pollen tube guidance.

Transcriptional responses to growth in high environmental calcium concentrations were characterized and compared between wild-type and mutant Arabidopsis plants containing a knockout mutation in the gene encoding a cyclic nucleotide-gated channel (CNGC2). We show that the transcriptional profile of cngc2 plants grown in normal media resembled that from wild-type plants grown under elevated exogenous calcium conditions. The mutant grown in high-calcium media exhibited transcriptional changes not seen in the wild-type. The pattern of transcription suggests that adaptation to high external calcium overlaps with responses towards various biotic and abiotic stresses.

The CDPK-SnRK superfamily consists of seven types of serine-threonine protein kinases: calcium-dependent protein kinase (CDPKs), CDPK-related kinases (CRKs), phosphoenolpyruvate carboxylase kinases (PPCKs), PEP carboxylase kinase-related kinases (PEPRKs), calmodulin-dependent protein kinases (CaMKs), calcium and calmodulin-dependent protein kinases (CCaMKs), and SnRKs. Within this superfamily, individual isoforms and subfamilies contain distinct regulatory domains, subcellular targeting information, and substrate specificities. Our analysis of the Arabidopsis genome identified 34 CDPKs, eight CRKs, two PPCKs, two PEPRKs, and 38 SnRKs. No definitive examples were found for a CCaMK similar to those previously identified in lily (Lilium longiflorum) and tobacco (Nicotiana tabacum) or for a CaMK similar to those in animals or yeast. CDPKs are present in plants and a specific subgroup of protists, but CRKs, PPCKs, PEPRKs, and two of the SnRK subgroups have been found only in plants. CDPKs and at least one SnRK have been implicated in decoding calcium signals in Arabidopsis. Analysis of intron placements supports the hypothesis that CDPKs, CRKs, PPCKs and PEPRKs have a common evolutionary origin; however there are no conserved intron positions between these kinases and the SnRK subgroup. CDPKs and SnRKs are found on all five Arabidopsis chromosomes. The presence of closely related kinases in regions of the genome known to have arisen by genome duplication indicates that these kinases probably arose by divergence from common ancestors. The PlantsP database provides a resource of continuously updated information on protein kinases from Arabidopsis and other plants.