Exine and Aperture Patterns on the Pollen Surface: Their Formation and Roles in Plant Reproduction

Abstract

Pollen grains, the male gametophytes of seed plants, surround themselves with a complex pollen wall for protection from various environmental stresses. The deposition and assembly of exine, the outer layer of the pollen wall, lead to the formation of patterns on the pollen surface that are species specific, tremendously diverse, and often very beautiful. These patterns arise due to exine's assembly into various nano‐ and microstructures, and due to the absence of exine deposition at certain areas of the pollen surface. The areas that have reduced exine deposition, or lack it completely, are known as pollen apertures, and their patterns are also species specific and highly variable. Although the intricate patterns of exine and apertures have been drawing attention for centuries, it is still not clear how exactly they develop, what genes are involved in their formation, and what purpose they serve. Here, we review the current state of knowledge about the exine and aperture patterns, their perceived roles in plant reproduction, and the cellular and molecular mechanisms that guide their formation.

Arabidopsis Protein Kinase D6PKL3 Is Involved in the Formation of Distinct Plasma Membrane Aperture Domains on the Pollen Surface

“…Pollen apertures exhibit tremendous diversity across species in regard to their numbers, positions, and morphology. They typically develop in a given species with remarkable precision and provide an excellent model for studying how cells specify and create distinct cellular and extracellular domains (Wang and Dobritsa, 2018). The large variety of aperture patterns in nature suggests that the system might be fairly responsive to genetic perturbations.…”

“…The pollen surface is protected by the pollen wall exine, the specialized sporopollenin-based cell wall, which in most plants is deposited nonuniformly, leaving gaps that are either not covered by exine or have reduced exine deposition (Walker and Doyle, 1975;Furness and Rudall, 2004). These gaps are known as pollen apertures, and they play a role in plant reproduction as sites for water transport and pollen tube germination, as well as architectural details that help pollen accommodate changes in volume (Wang and Dobritsa, 2018). Apertures exhibit species-specific variations in their morphology, number, and positions and produce a variety of pollen surface patterns, with the most common pattern in eudicots consisting of three equidistant longitudinal apertures (Wodehouse, 1935;Walker and Doyle, 1975;Furness and Rudall, 2004).…”

Unraveling the Deep Genetic Architecture for Seedlessness in Grapevine and the Development and Validation of a New Set of Markers for VviAGL11-Based Gene-Assisted Selection

“…Among the best candidate genes involved in this model that explains male or female sterility are INP1, APT3 and YABBY that was discussed above. Pollen grains are surrounded by a very resistant wall interrupted by apertures, areas where the wall is thinner or softer, that play a key role because the pollen tube growth is initiated at these apertures, through them the pollen tube can reach out from the inside and transport the sperm cells to the female structures [65]. Pollen aperture factor INP1 is absolutely required for aperture formation [66].…”

Demystifying and Unravelling the Factual Molecular Structure of the Biopolymer Sporopollenin

“…(Passifloraceae) sporopollenin SEM image is shown in SI-figure 14, showing a circular aperture with a cross-linked network built on it. [45] Although passiflora sp. is a different type of sporopollenin than the one of lycopodium clavatum, its SEM image makes sense with the building units identified in this manuscript (circular polymer and Dendrimer-like network) and help in better visualization of how these units may be connected together.…”