Abstract
Pollen tube (PT) growth as a key step for successful fertilization is essential for angiosperm survival and especially vital for grain yield in cereals. The process of PT growth is regulated by many complex and delicate signaling pathways. Among them, the calcium/calcium-dependent protein kinases (Ca2+/CPKs) signal pathway has become one research focus, as Ca2+ ion is a well-known essential signal molecule for PT growth, which can be instantly sensed and transduced by CPKs to control myriad biological processes. In this review, we summarize the recent progress in understanding the Ca2+/CPKs signal pathway governing PT growth. We also discuss how this pathway regulates PT growth and how reactive oxygen species (ROS) and cyclic nucleotide are integrated by Ca2+ signaling networks.
Highlights
The calcium ion (Ca2+), as a central second messenger in plants, coordinates a variety of physiological responses by binding the calcium sensors, which decode the calcium signatures and elicit different cellular responses
A number of AtCDPKs are mainly expressed in pollen, indicating their involvement in pollen development and/or pollen tube (PT) growth, which is crucial for sexual reproduction in flowering plants
We summarize the key findings of the Ca2+/calcium-dependent protein kinases (CPKs) signaling pathway in PT growth and further address the interrelationship between Ca2+ signaling with other complex signaling networks such as reactive oxygen species (ROS) and cyclic nucleotide
Summary
The calcium ion (Ca2+), as a central second messenger in plants, coordinates a variety of physiological responses by binding the calcium sensors, which decode the calcium signatures and elicit different cellular responses. The different tissue- and developmental-stage expressions of the CPKs possess specific functions; for example, AtCPK28 and AtCPK3/4/6/11 have roles in shoot and root development, respectively, and AtCPK6/33 may be involved in the regulation of floral transition (see the review by Yip Delormel and Boudsocq, 2019). Upon pollen landing on the stigma, the PT rapidly elongates and penetrates the transmitting tract to deliver the immotile sperm to the ovule for double fertilization (Higashiyama and Yang, 2017). During this process, Ca2+ is well-known to control pollen germination, PT growth, and intercellular communication between PT and female tissue (Ge et al, 2007; Zheng et al, 2019).
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