The Role of Female and Male Genes in Regulating Pollen Tube Guidance in Flowering Plants

Abstract

In flowering plants, fertilization is a complex process governed by precise communication between the male and female gametophytes. This review focuses on the roles of various female gametophyte cells-synergid, central, and egg cells-in facilitating pollen tube guidance and ensuring successful fertilization. Synergid cells play a crucial role in attracting the pollen tube, while the central cell influences the direction of pollen tube growth, and the egg cell is responsible for preventing polyspermy, ensuring correct fertilization. The review also examines the role of the pollen tube in this communication, highlighting the mechanisms involved in its growth regulation, including the importance of pollen tube receptors, signal transduction pathways, cell wall dynamics, and ion homeostasis. The Ca²⁺ concentration gradient is identified as a key factor in guiding pollen tube growth toward the ovule. Moreover, the review briefly compares these communication processes in angiosperms with those in non-flowering plants, such as mosses, ferns, and early gymnosperms, providing evolutionary insights into gametophytic signaling. Overall, this review synthesizes the current understanding of male-female gametophyte interactions and outlines future directions for research in plant reproductive biology.

Keywords: female gametophyte; pollen tube guidance; polyspermy; polytubey block.

Figure 1

The pollen tube is targeting the ovule. LUREs, TICKETs, and XIUQIUs secreted by synergids are attractants that attract pollen tubes. LUREs specifically bind to PRK6 and MDIS1-MIK1/2 at the tip of pollen tubes. FER interacts with LRE, HERK1, and ANJ to recruit NTA from the Golgi to the filiform apparatus and form a Ca²⁺ channel, mediating pollen tube rupture. ECS1 secreted by egg cells can cleave LURE to avoid polyspermy. The CCG located in the central cell and its binding protein CBP1 are also involved in pollen tube guidance. SAL1/2 is secreted into the micropyle after fertilization failure to restore fertilization ability. The MLO at the tip of the pollen tube recruits the Ca²⁺ channel CNGC18 to the membrane. At the same time, when the pollen tube reaches the micropyle, the peptide ligand RALF4/19 of ANX-BUPS is competitively replaced by RALF34, inducing the rupture of the pollen tube. RALF6/7/16/36/37 binds to the FER-ANJ-HERK1 complex to establish a polytubey block.

Figure 2

Pollen tube during growth. CHX21/23 located in the endoplasmic reticulum and CHX17/18/19 located in the sperm membrane are K⁺/H⁺ exchangers. SUN3/4/5-POD1-CRT3 regulates sorting of LRR-RKs to the plasma membrane. APTG1 affects the localization of GPI-anchored proteins such as COBL10. BUPS1 maintains the integrity of pollen tubes in the transmitting tract through a series of cascading reactions.