ObjectivePollen germination and pollen tube growth play a critical role in reproductive process of flowering plants. Pollen germination and pollen tube growth is regulated directly or indirectly by many factors, such as calmodulin-like proteins (CMLs). However, very little research has focused on the function of CMLs till now. The aim of this paper is to reveal the role of CML proteins in the competitive advantage of pollen, and to provide a theoretical foundation for further exploring the molecular mechanism of CMLs in plant pollen competitive advantage.

MethodThis paper comprehensively summarizes the structure, expression level, cell localization and mechanisms of CMLs proteins involved in the regulation of pollen germination and pollen tube growth, and analyzes the pollen competition phenomena in different plants.

ResultThere were about four conserved EF-hand domains in CMLs. When CMLs bind to Ca²⁺, its conformation changes enhanced its binding ability to downstream receptor proteins, and initiated Ca²⁺ dependent cascade signal amplification effect, which resulted in changes in Ca²⁺ concentration in pollen tube and influenced the formation of Ca²⁺ concentration gradient from germination aperture to the top of pollen tube, thus regulating the normal growth of pollen tube. The expression of CML proteins can also affect the concentration of Mg²⁺, NO and the binding of Ca²⁺ to EF-hand domains and the orientation of pollen tube growth. Different CML proteins had different physiological functions. Among them, CML proteins involved in pollen germination and pollen tube growth were mainly expressed in plant floral organs. During fertilization of some flowering plants, different ploidy pollens may have different germination rates and growth rates due to differences in genome size or nutrient content.

ConclusionCMLs proteins may affect the process of pollen germination in vivo by differentially expressing in different ploidy pollens, and make them show competitive advantage in a certain period of time.