Pollen-expressed RLCKs control pollen tube burst

Role of Tyrosine Phosphorylation in PEP1 Receptor 1(PEPR1) in Arabidopsis thaliana

Leucine-rich repeat receptor-like kinases (LRR-RLKs) have evolved to perceive environmental changes. Among LRR-RLKs, PEPR1 perceives the pep1 peptide and triggers defense signal transduction in Arabidopsis thaliana. In the present study, we focused on PEPR1 and PEPR2, which are the receptors of pep1, to understand the role of tyrosine phosphorylation. PEPR1-CD (cytoplasmic domain) recombinant protein exhibited strong tyrosine autophosphorylation, including threonine autophosphorylation. We subjected all tyrosine residues in PEPR1-CD to site-directed mutagenesis. The recombinant proteins were purified along with PEPR1-CD, and Western blotting was performed using a tyrosine-specific antibody. Among the 13 tyrosine residues in PEPR1-CD, the PEPR1(Y995F)-CD recombinant protein showed significantly reduced tyrosine autophosphorylation intensity compared to PEPR1-CD and other tyrosine mutants, despite little change in threonine autophosphorylation. To confirm the autophosphorylation site, we generated a phospho-specific peptide Ab, pY995. As a result, Tyr-995 of PEPR1-CD was a major tyrosine autophosphorylation site in vitro. To understand the function of tyrosine phosphorylation in vivo, we generated transgenic plants, expressing PEPR1-Flag, PEPR1(Y995F)-Flag, and PEPR1(Y995D)-Flag in a pepr1/2 double mutant background. Interestingly, the root growths of PEPR1(Y995F)-Flag and PEPR1(Y995D)-Flag were not inhibited by pep1 peptide treatment, compared to Col-0 and PEPR1-Flag (pepr1/2) transgenic plants. Also, we analyzed downstream components, which included PROPEP1, MPK3, WRKY33, and RBOHD gene expressions in four different genotypes (Col-0, PEPR1-Flag, PEPR1(Y995F)-Flag, and PEPR1(Y995D)-Flag) of plants in the presence of the pep1 peptide. Interestingly, the expressions of PROPEP1, MPK3, WRKY33, and RBOHD were not regulated by pep1 peptide treatment in PEPR1(Y995F)-Flag and PEPR1(Y995D)-Flag transgenic plants, in contrast to Col-0 and PEPR1-Flag. These results suggest that specific tyrosine residues play an important role in vivo in the plant receptor function.

Advances in research on the control of pollen tube growth by calcium in higher plants

The function of the pollen tube in higher plants is to deliver two male gametes to the embryo sac to ensure successful double fertilization. During this process, many interactions occur among pollen tubes and pistil cells and tissues. Calcium ion (Ca2 +) dynamics mediate these interactions to ensure that the pollen tube grows with correct polarity and orientation to reach its target, the embryo sac. The pistil tissue, which contains abundant Ca2+, attracts the growing pollen tube via changes in Ca2+. Recent studies have shed light on the mechanisms of vacuole biogenesis and the Ca2+ action pathway in the growing pollen tube. This successfully explains the distribution characteristics of high Ca2+ at the tip of the pollen tube and the physiological mechanism of Ca2+ controlling pollen tube growth. In last stage of pollen tube growth, some studies indicated that the cessation of pollen tube growth and breaking of the tube in embryo sac maybe related to Ca2+ dynamic, which finishes its complex journey of pollen tube in vivo.

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

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.