Rice calcium-dependent protein kinase isoforms OsCDPK2 and OsCDPK11 show different responses to light and different expression patterns during seed development

We investigated the spatial and temporal expression patterns of two rice ca lcium-dependent protein kinases (CDPKs), OsCDPK2 and OSCDPK11, using isofor m-specific antisera. Bands of the expected molecular sizes for OsCDPK2 (59 kDa) and OsCDPK11 (61 kDa) were detected on western blots. OsCDPK2 and OsCD PK11 mRNA and protein levels increased in unison during flower development. However, at the onset of seed development, the protein expression profiles diverged significantly. OsCDPK2 protein was expressed at low levels during early seed development, but increased to high levels that were maintained in later stages (20 days after fertilisation, DAF). Conversely, OsCDPK11 pr otein levels were high at the beginning of seed development, but fell rapid ly from 10 DAF onwards. This decrease in the level of OsCDPK11 protein was associated with the abundant synthesis of a truncated mRNA species. OsCDPK2 expression was also closely associated with light perception. OsCDPK2 prot ein was barely detectable in green leaves exposed to light, but levels incr eased sharply when plants were shifted to darkness. Initially, this increas e reflected a rapid elevation in the levels of OsCDPK2 mRNA, which was norm ally located in the mesophyll. Conversely, OsCDPK11 mRNA and protein levels were unaffected by light. These data strongly indicate that two rice CDPK isoforms have different functions in seed development and in response to li ght in leaves.