EXO70C2 is a key regulatory factor for optimal tip growth of pollen Journal Article

Author(s): Synek, Lukáš; Vukašinović, Nemanja; Kulich, Ivan; Hála, Michal; Aldorfová, Klára; Fendrych, Matyas; Žárský, Viktor
Article Title: EXO70C2 is a key regulatory factor for optimal tip growth of pollen
Affiliation IST Austria
Abstract: The exocyst, a eukaryotic tethering complex, coregulates targeted exocytosis as an effector of small GTPases in polarized cell growth. In land plants, several exocyst subunits are encoded by double or triple paralogs, culminating in tens of EXO70 paralogs. Out of 23 Arabidopsis thaliana EXO70 isoforms, we analyzed seven isoforms expressed in pollen. Genetic and microscopic analyses of single mutants in EXO70A2, EXO70C1, EXO70C2, EXO70F1, EXO70H3, EXO70H5, and EXO70H6 genes revealed that only a loss-of-function EXO70C2 allele resulted in a significant male-specific transmission defect (segregation 40%:51%:9%) due to aberrant pollen tube growth. Mutant pollen tubes grown in vitro exhibited an enhanced growth rate and a decreased thickness of the tip cell wall, causing tip bursts. However, exo70C2 pollen tubes could frequently recover and restart their speedy elongation, resulting in a repetitive stop-and-go growth dynamics. A pollenspecific depletion of the closest paralog, EXO70C1, using artificial microRNA in the exo70C2 mutant background, resulted in a complete pollen-specific transmission defect, suggesting redundant functions of EXO70C1 and EXO70C2. Both EXO70C1 and EXO70C2, GFP tagged and expressed under the control of their native promoters, localized in the cytoplasm of pollen grains, pollen tubes, and also root trichoblast cells. The expression of EXO70C2-GFP complemented the aberrant growth of exo70C2 pollen tubes. The absent EXO70C2 interactions with core exocyst subunits in the yeast two-hybrid assay, cytoplasmic localization, and genetic effect suggest an unconventional EXO70 function possibly as a regulator of exocytosis outside the exocyst complex. In conclusion, EXO70C2 is a novel factor contributing to the regulation of optimal tip growth of Arabidopsis pollen tubes.
Journal Title: Plant Physiology
Volume: 174
Issue 1
ISSN: 1532-2548
Publisher: American Society of Plant Biologists  
Date Published: 2017-05-01
Start Page: 223
End Page: 240
Sponsor: Czech Science Foundation (grant no. 15-24711S), Ministry of Education of the Czech Republic (grant no. NPUI LO1417)
DOI: 10.1104/pp.16.01282
Notes: We thank Martin Potocky (IEB ASCR) for helpful discussions on this project, on data presentation, and for box plot rendering; Roman Pleskot (IEB ASCR) for the sequence identity calculation; David E. Jarvis (KAUST) for language corrections; and Tsuyoshi Nakagawa (Research Institute of Molecular Genetics, Shimane University) for providing pGWB vectors. The T-DNA GABI lines analyzed here were generated in the context of the GABI-Kat program and provided by B. Weisshaar (Max Planck Institute for Plant Breeding Research).
Open access: no