Calcium-dependent protein kinases (CDPKs) in plants are essential in its
tolerance to abiotic stresses and in seed development. However, only a few
rice CDPK functions have been known while and its role in spikelet fertility
is still unclear.

A rice CDPK gene, OsCPK9, was cloned and characterized. It was then
overexpressed in some individuals and was repressed, through RNA
interference, in others. The results revealed the positive role the OsCPK9
plays in drought stress tolerance as well as in spikelet fertility. OsCPK9
improves drought stress tolerance through the enhancement of stomatal
closure and by improving the plants' osmotic adjustment ability. It
increases spikelet fertility through improvement of pollen viability.

Shoot and root elongation had enhanced sensitivity to ABA in
OsCPK9-overexpressing plants compared to the wild-type. Overexpression and
RNA interference of OsCPK9 affected both the transcript levels of ABA- and
stress-responsive genes. These results revealed the positive effect of
OsCPK9 in the regulation of abiotic stress tolerance, spikelt fertility and
ABA sensitivity.

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