LORELEI-LIKE GPI-ANCHORED PROTEINS 2/3 Regulate Pollen Tube Growth as Chaperones and Coreceptors for ANXUR/BUPS Receptor Kinases in Arabidopsis

Structural basis for recognition of RALF peptides by LRX proteins during pollen tube growth

“…The redundant signaling peptides RALF4 and RALF19 ensure pollen tube integrity and growth by interacting with two distinct protein families, the malectin-domain CrRLK1L membrane receptor kinases (1)(2)(3)(4), and the cell-wall monitoring leucine-rich repeat (LRR) extensin proteins (LRXs) (5,6). Together with ANXUR1/2 and BUDDHA'S PAPER SEAL1/2 (BUPS1/2), the pollen-expressed LORELEI-like GLYCOLPHOSPHATIDYLINOSITOL (GPI)-ANCHORED PROTEINS2 (LLG2) and LLG3 are also required for monitoring pollen tube integrity and are part of the same signaling complex (2,7). Recent structural data of the ternary RALF23-LLG2-FERONIA (FER) (8) complex suggests a shared mechanism for recognition of RALF peptides by LLG proteins, where the N-terminal region of the peptide is responsible for inducing an allosteric change in LLG to nucleate assembly with the corresponding CrRLK1L receptor (9).…”

ROS in the Male–Female Interactions During Pollination: Function and Regulation

“…An Arabidopsis receptor complex was reported to control the maintenance of pollen tube integrity during its growth in the style, which is composed of pollen-specific CrRLK1L subfamily receptor-like kinases ANXUR1/2 (ANX1/2), Buddha's Paper Seal 1/2 (BUPS1/2) and LORELEI-like-GPI-anchored protein 2/3 (LLG2/3). This complex is localized in the apical membrane of the pollen tube and functions by perceiving the autocrine peptide ligands, rapid alkalinization factor 4/19 (RALF4/19) (Boisson-Dernier et al, 2009;Miyazaki et al, 2009;Ge et al, 2017;Mecchia et al, 2017;Feng et al, 2019;Ge et al, 2019b). The pollen tube of the ralf4,19 double mutant also displays precocious rupture in vitro and inhibited growth in the transmitting tract, which is similar to that of the llg2,3, bups1,2 and anx1,2 double mutants.…”

“…The pollen tube of the ralf4,19 double mutant also displays precocious rupture in vitro and inhibited growth in the transmitting tract, which is similar to that of the llg2,3, bups1,2 and anx1,2 double mutants. However, RALF4 induced the production of ROS in the pollen tube that stimulates the pollen tube growth and inhibits the pollen burst in vitro (Feng et al, 2019). An Arabidopsis llg2,3 double mutant pollen tube exhibited reduced ROS levels and burst after germination in vitro, and the application of exogenous H 2 O 2 rescued the rupture of the pollen tube (Feng et al, 2019).…”

“…However, RALF4 induced the production of ROS in the pollen tube that stimulates the pollen tube growth and inhibits the pollen burst in vitro (Feng et al, 2019). An Arabidopsis llg2,3 double mutant pollen tube exhibited reduced ROS levels and burst after germination in vitro, and the application of exogenous H 2 O 2 rescued the rupture of the pollen tube (Feng et al, 2019). As suggested (Boisson-Dernier et al, 2013), the LLG-BUPS-ANX receptor complex functions upstream of RBOHH/J and regulates their activities to coordinate ROS production and Ca 2+ homeostasis in regulating the pollen tube growth in the pistil.…”

“…As suggested (Boisson-Dernier et al, 2013), the LLG-BUPS-ANX receptor complex functions upstream of RBOHH/J and regulates their activities to coordinate ROS production and Ca 2+ homeostasis in regulating the pollen tube growth in the pistil. In this process, the activities of RBOHs are mediated by RopGEF-ROP downstream of ANX1/2 (Zhu et al, 2018;Feng et al, 2019) ( Figure 1B).…”