Reproductive Multitasking: The Female Gametophyte

Abstract

Fertilization of flowering plants requires the organization of complex tasks, many of which become integrated by the female gametophyte (FG). The FG is a few-celled haploid structure that orchestrates division of labor to coordinate successful interaction with the sperm cells and their transport vehicle, the pollen tube. As reproductive outcome is directly coupled to evolutionary success, the underlying mechanisms are under robust molecular control, including integrity check and repair mechanisms. Here, we review progress on understanding the development and function of the FG, starting with the functional megaspore, which represents the haploid founder cell of the FG. We highlight recent achievements that have greatly advanced our understanding of pollen tube attraction strategies and the mechanisms that regulate plant hybridization and gamete fusion. In addition, we discuss novel insights into plant polyploidization strategies that expand current concepts on the evolution of flowering plants.

The emerging role of small RNAs in ovule development, a kind of magic

“…They leave open a minute pore, the micropyle, through which the pollen tube will enter the embryo sac during double fertilization. Consequently, the two released sperm cell nuclei will fuse with the egg cell and the central cell, generating the zygote and the endosperm, respectively, whereas the integuments will develop into the seed coat (Hater et al 2020 ).

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Comparative transcriptomic analysis reveals conserved transcriptional programs underpinning organogenesis and reproduction in land plants

“…Parallel with innovations of vegetative cell types, land plants evolved new reproductive structures such as spores, pollen, embryo sacs, and seeds together with the gradual reduction of the haploid phase. In contrast to algae, mosses, and ferns that require moist habitats, the male and female gametophytes of gymnosperms and angiosperms are strongly reduced, consisting of only a few cells, including the gametes 10,11 . Moreover, sperm cells have lost their mobility and use pollen grains as a protective vehicle for long-distance transport and a pollen tube for their delivery deep into maternal reproductive tissues 12,13 .…”

“…Analysis of male germline differentiation, for example, has led to the identification of Arabidopsis DUO POLLEN 1 (DUO1) and the network of genes it controls, which include the fertilization factors, HAP2/GCS1 and GEX2 22 . However, as novel genes are still being discovered that control the development of male and female gametes 10,11 or their functions 23,24 , it is clear that our knowledge of the molecular basis of gamete formation and function is far from complete.…”

Receptor-like protein kinases in plant reproduction: Current understanding and future perspectives

“…After a series of continuous developmental processes, pollen grains, the male gametophytes, are finally formed in the anther to produce sperm cells ( Sanders et al., 1999 ; Ma, 2005 ; Chang et al., 2011 ; Schmidt et al., 2015 ). Ovules, which are packaged and protected by the carpels, provide space for the development of embryo sacs, the female gametophytes that generate the egg and the central cell ( Yang et al., 2010 ; Schmidt et al., 2015 ; Hater et al., 2020 ). Reproduction of Arabidopsis requires the transfer of sperm cells into the embryo sac, where double fertilization is performed to generate the embryo and endosperm ( Lau et al., 2012 ; Shin et al., 2020 ; Hafidh and Honys, 2021 ; Kim et al., 2021 ).…”