About this Research Topic
This Research Topic is part of the Regulation of Pollen Tube Growth series:
Regulation of Pollen Tube Growth
During fertilization, seed plants require polarized cell growth to enable gamete transport. The polarized growth occurs via apical expansion of the pollen tube requiring the deposition of new cell wall material exclusively at the apex. Correct pollen tube growth depends on an elaborate mechanism that integrates different molecular and cytological subprocesses and is controlled by signaling molecules exchanged between pollen tubes and the female apparatus. Therefore, the pollen tube represents an excellent model for studying cell shaping and how external signals modify the shape and ability to grow. Pollen tubes are the target of stressful abiotic conditions that can adversely affect the reproductive capacity. Additionally, they are carriers of allergens that have caused pandemic human health problems.
This Research Topic aims to collect contributions to the understanding of molecular mechanisms that regulate pollen tube growth, from the perception and transduction of extracellular signals, to the role of cytoskeleton in redistributing cell wall components, to the integration of these mechanisms into the general process that determines the pollen tube shape, its growth and the success of plant fertilization.
This Research Topic will cover the following points:
• Cell signaling. Exchanging information between pollen tubes and female reproductive structures is critical because it promotes and guides the growth of tubes and regulates the recognition and rejection of self-incompatible pollen. Genes and key molecules involved in guiding pollen tubes have been partially identified but a broader view of how growth is orchestrated is still lacking. Probably the tube apex is the region where external signals are perceived and used to control tube growth. Enzyme receptors, GTPases, transmembrane ion fluxes, gradients and dynamics of intracellular ions, local accumulation of ROS, presence of polyamines, are just a few examples of factors needed to polarize pollen tubes and to maintain tip growth.
• Exocytosis and endocytosis during pollen tube growth. To allow tube growth, exocytosis and endocytosis are strongly active to supply and recycle the plasma membrane and to intake components of the extracellular matrix, partially secreted from female tissues, sometimes sequestering them in organelles. Some molecules released by pollen tubes into the extracellular matrix are important regulators of tube growth.
• Nanovesicles, proteins and allergens role in successful fertilization? The release of pollen tube nanovesicles is important for proper tube growth: nanovesicles contain different proteins, many of which have roles in metabolism and signaling, in protein synthesis and processing, in cell wall expansion, in membrane transport. Sometimes, some of these proteins are allergens and contributes to pollen sensitization. However, the functions of such allergens are crucial for pollen development, thus, inhibiting their expression would simultaneously inhibit fertilization.
• Cell wall and cytoskeleton dynamics. Exo- and endocytosis regulate the assembly and deposition of the cell wall, whose consistency is important for the proper growth and morphogenesis of cells. The structure of the pollen tube cell wall is generally known, but not so the molecular mechanism controlling deposition and cell wall dynamics. Accumulation of secretory vesicles are associated with the dynamics of the cytoskeleton along with a combination of motor and non-motor proteins, most likely depending on both signal transduction pathway and ion dynamics.
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