EXO70A2 Is Critical for Exocyst Complex Function in Pollen Development

Abstract

A pollen-specific component of the exocyst, a protein complex regulating cellular secretion, plays an important role in pollen development and function in Arabidopsis.

Regulation of Exocyst Function in Pollen Tube Growth by Phosphorylation of Exocyst Subunit EXO70C2

“…Abnormal swelling of the tip-shape morphology was observed only exceptionally in YFP:EXO70A2-expressing pollen tubes. Our data for Arabidopsis EXO70A2 ( Marković et al, 2020 ) show that this isoform is evolutionarily adapted to positively support pollen development, germination and pollen tube growth. Its interference with pollen tube growth of tobacco might be a result of the competition of endogenous tobacco EXO70A2 with the ectopically overexpressed Arabidopsis EXO70A2 for functional exocyst assembly.…”

“…Arabidopsis EXO70A2, another EXO70 subunit highly expressed in pollen, was used as an alternative control ( Marković et al, 2020 ). We found that it also partly inhibited the speed of elongation and expansion but significantly less than EXO70C2 ( Figure 4 ).…”

“…The full list of sequences is provided in Supplementary Figure S1 . Protein sequence alignment was performed using the MAFFT G-INS-I algorithm ( Katoh and Standley, 2013 ) in the Jalview software ( Waterhouse et al, 2009 ) and maximum-likelihood phylogeny reconstructed as described in Marković et al (2020) . Final sequence conservation analysis of the phosphosites was performed on 23 EXO70C1 and 20 EXO70C2 paralogs and orthologs from 17 dicot genomes using WebLogo algorithm ( Crooks et al, 2004 ).…”

“…Arabidopsis loss-of-function (LOF) mutants of SEC3a , SEC5a/b , SEC6 , SEC8 , or SEC15a have very short and depolarized pollen tubes, which correlates with a failure to transmit the mutant alleles through the male gamete ( Cole et al, 2005 ; Hála et al, 2008 ; Bloch et al, 2016 ). The two EXO70A isoforms, EXO70A1 ( Synek et al, 2006 ) and EXO70A2 ( Marković et al, 2020 ), seem to have a general housekeeping function during exocytosis in the sporophyte and the male gametophyte, respectively. Partially resembling the phenotypes of LOF mutants of core exocyst subunits, exo70A2 pollen grains germinate poorly and produce short, thick, slowly growing pollen tubes ( Beuder et al, 2020 ; Marković et al, 2020 ).…”

“…The two EXO70A isoforms, EXO70A1 ( Synek et al, 2006 ) and EXO70A2 ( Marković et al, 2020 ), seem to have a general housekeeping function during exocytosis in the sporophyte and the male gametophyte, respectively. Partially resembling the phenotypes of LOF mutants of core exocyst subunits, exo70A2 pollen grains germinate poorly and produce short, thick, slowly growing pollen tubes ( Beuder et al, 2020 ; Marković et al, 2020 ). In sharp contrast, LOF of Arabidopsis EXO70C2 results in stop-and-go growth dynamics where phases with abnormally high growth rates are interrupted by pollen tube tip bursts and recovery, ultimately resulting in pollen tube rupture ( Synek et al, 2017 ).…”