OsCML17 a pollen-expressed calmodulin-like protein regulates pollen germination and tube growth in rice (Oryza...

The rice pollen-specific calmodulin-like protein OsCML17 contributes to fertilization by regulating pollen germination and pollen tube elongation, and is localized to the endoplasmic reticulum and plasma membrane. In angiosperms, successful fertilization relies on the precise growth of the pollen tube growth. Calcium ion (Ca²⁺) regulates various physiological responses and plays a critical role in pollen germination and pollen tube growth. Calmodulin-like proteins (CMLs), which consist of EF-hand motifs, function as Ca²⁺ sensors that detect changes in intracellular Ca²⁺ concentrations and regulate specific signaling pathways. Despite their significance, the expression dynamics and functional significance of CMLs in rice remain largely unexplored. In this study, we examined expression profiles and structural properties of 32 CML genes in rice to identify those preferentially expressed in pollen. OsCML17 exhibited strong expression in rice mature anthers containing tricellular pollen and was localized to both the endoplasmic reticulum and the plasma membrane in the tobacco cells. Knockout mutants of OsCML17 generated by CRISPR/Cas9 exhibited consistently reduced pollen germination rates and shorter pollen tubes. Moreover, the OsCML17 transcript was markedly decreased in the mature pollen of the madstri mutant, indicating potential transcriptional regulation by MADS-box factors. Overall, these findings suggest that OsCML17 functions as an important factor regulating pollen germination and tube elongation in rice.