VPS18-regulated vesicle trafficking controls the secretion of pectin and its modifying enzyme during pollen tube growth in Arabidopsis

Abstract

In eukaryotes, homotypic fusion and vacuolar protein sorting (HOPS) as well as class C core vacuole/endosome tethering (CORVET) are evolutionarily conserved membrane tethering complexes that play important roles in lysosomal/vacuolar trafficking. Whether HOPS and CORVET control endomembrane trafficking in pollen tubes, the fastest growing plant cells, remains largely elusive. In this study, we demonstrate that the four core components shared by the two complexes, Vacuole protein sorting 11 (VPS11), VPS16, VPS33 and VPS18, are all essential for pollen tube growth in Arabidopsis thaliana and thus for plant reproduction success. We used VPS18 as a representative core component of the complexes to show that the protein is localized to both multivesicular bodies (MVBs) and the tonoplast in a growing pollen tube. Mutant vps18 pollen tubes grew more slowly in vivo, resulting in a significant reduction in male transmission efficiency. Additional studies revealed that membrane fusion from MVBs to vacuoles is severely compromised in vps18 pollen tubes, corroborating the function of VPS18 in late endocytic trafficking. Furthermore, vps18 pollen tubes produce excessive exocytic vesicles at the apical zone and excessive amounts of pectin and pectin methylesterases in the cell wall. In conclusion, this study establishes an additional conserved role of HOPS/CORVET in homotypic membrane fusion during vacuole biogenesis in pollen tubes and reveals a feedback regulation of HOPS/CORVET in the secretion of cell wall modification enzymes of rapidly growing plant cells.

The egg cell is preferentially fertilized in Arabidopsis double fertilization

“…In the other strategy, gametophytes carrying the mutated gene are distinguished by fluorescence labels. This approach has been employed to successfully separate and collect mutant pollen of vacuolar protein sorting‐associated protein 41 (VPS41) and VPS18, two essential proteins involved in endomembrane trafficking (Hao et al, 2016; Zhong et al, 2020; Hou et al, 2021).…”

The phospholipid flippase ALA3 regulates pollen tube growth and guidance in Arabidopsis

“…The process underlying the polar distribution of proteins depends on the establishment and maintenance of directional transport. The endomembrane system is needed for the directional transport of proteins to specific sites, the strong accumulation of proteins, and further recycling by endocytosis and redistribution between the trans-Golgi network/endosome and plasma membrane ( Yang et al, 2020 ; Dubois and Jaillais, 2021 ; Hou et al, 2021 ; Ruan et al, 2021 ). Phospholipid transport catalyzed by P4-ATPase plays an important role in vesicle transport.…”

Vesicle trafficking in Arabidopsis pollen tubes

“…Transient expression of AtPMEI2 in tobacco promoted pollen tube growth while that of PME did the opposite [84]. VAN-GUARD1 (VGD1) and AtPPME1 are two pectin methylesterase, whose functional loss or mistargeting resulted in defective pectin network and abnormal pollen tube growth [85][86][87]. In addition to pectin, cellulose also is an important part of the pollen tube wall.…”

“…Recent studies indicated an essential role of these tethering complexes in pollen tube growth. Functional loss of Arabidopsis Vps41 resulted in failed style penetration of pollen tubes [114] and that of Vps11, Vps16, and Vps18 substantially compromised this process [31,87,115]. Defective pollen tube growth due to mutations of the tethering complexes is not only associated with abnormal vacuolar morphology and vesicle-tonoplast fusion but often with abnormal deposition of cell wall components [87].…”

“…Mutations of vacuolar trafficking regulators also influenced the secretory pathway. Functional loss of Vps18 not only impaired vacuolar targeting of tonoplast proteins but also enhanced exocytosis, which led to excessive deposition of pectin and a more rigid pollen tube wall [87]. Similarly, functional loss of Vps41 caused mistargeting of tonoplast proteins to the PM in pollen tubes [112].…”