ANXUR Receptor-Like Kinases Coordinate Cell Wall Integrity with Growth at the Pollen Tube Tip Via NADPH Oxidases

Abstract

Pollen tubes grow extremely rapidly to effect fertilization in plants. ANXUR receptor-like kinases facilitate this growth by linking the intracellular growth machinery of pollen tubes to the status of the extracellular matrix via H2O2 and Ca2+ signaling.

Receptor-like cytoplasmic kinase MARIS functions downstream of Cr RLK1L-dependent signaling during tip growth

“…To study the effect of the R240C mutant form further, WT plants were transformed with both MRI-CFP and MRI R240C -CFP. Previously, we reported that overexpression of ANX1 mildly inhibits pollen germination and PT growth, most likely by triggering overaccumulation of secreted CW material (6). In transgenic lines with strong expression of MRI-CFP, only a few pollen grains displayed membrane invaginations and CW accumulation (n = 31 of 444 fluorescent PTs) (Fig.…”

“…To position MRI in the ANX1/2 signaling pathway, we tested whether overexpression of MRI and MRI R240C could rescue partially malesterile rbohH rbohJ mutant plants (6). All 32 independent T1 lines of rbohH rbohJ with MRI-CFP fluorescence remained partially sterile (e.g., for three independent T1 lines with high CFP expression, seed set was 8.5 ± 3.1, 8.8 ± 3.9, and 9.4 ± 4.2) similar to untransformed rbohH rbohJ plants (7.2 ± 2.1).…”

“…This phenotype also is seen when the ANX-RLKs are degraded by the endoplasmic reticulumassociated degradation pathway in the turan mutant affecting N-glycosylation (5). On the other hand, overexpression of ANXRLKs inhibits pollen germination and PT elongation, most likely because of the oversecretion of CW material (6). The ANXRLKs and their closest homolog FERONIA (FER) belong to the Catharanthus roseus RLK1-like (CrRLK1L) subfamily that has been investigated extensively as putative CW sensors involved in coordinating cell growth, cell-cell communication, defense against pathogens, and hormone signaling as well as CW remodeling and integrity (reviewed in refs.…”

“…This finding has been confirmed for at least one signaling component so far, namely the reactive oxygen species (ROS)-producing NADPH oxidases, also called "respiratory burst oxidase homologs" (Rboh). It was reported that RbohD/RbohF for THESEUS1 (THE1), RbohC for FER, and RbohH/RbohJ for ANX1/2 act downstream of the CrRLK1Ls in primary roots, root hairs, and PTs, respectively (6,19,22).…”

Apoplastic ROS production upon pollination by RbohH and RbohJ in Arabidopsis

“…1 Reactive oxygen species (ROS) accumulate at the tip of growing pollen tubes and 2 NADPH oxidases, respiratory burst oxidase homolog H (RbohH) and RbohJ, specifically localized in the plasma membrane of the growing tip 2 are involved in this accumulation. [2][3][4] The ROS are suggested to stimulate the plasma membrane Ca 2C -permeable channel(s) and induce Ca 2C influx into the cytoplasm. 5 The cytosolic Ca 2C rise in turn activates the ROS-producing activity of Rboh proteins by direct binding to the EF-hand motifs and by phosphorylation through the Ca 2C -dependent protein kinases, generating a positive feedback regulation that maintains the growth site to the tip during elongation (Fig.…”