title: EXO70C2 Is a Key Regulatory Factor for Optimal Tip Growth of Pollen.
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 23Arabidopsis thalianaEXO70 isoforms, we analyzed seven isoforms expressed in pollen. Genetic and microscopic analyses of single mutants inEXO70A2,EXO70C1,EXO70C2,EXO70F1,EXO70H3,EXO70H5, andEXO70H6genes revealed that only a loss-of-functionEXO70C2allele 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,exo70C2pollen tubes could frequently recover and restart their speedy elongation, resulting in a repetitive stop-and-go growth dynamics. A pollen-specific depletion of the closest paralog,EXO70C1, using artificial microRNA in theexo70C2mutant 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 ofexo70C2pollen 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.
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and lukas.synek@kaust.edu.sa zarsky@ueb.cas.cz.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.) lukas.synek@kaust.edu.sa zarsky@ueb.cas.cz.
authors.forename: Lukáš
authors.identifier: http://orcid.org/0000-0003-2111-2450
authors.initials: L
authors.lastname: Synek
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.).
authors.forename: Nemanja
authors.initials: N
authors.lastname: Vukašinović
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.).
authors.forename: Ivan
authors.identifier: http://orcid.org/0000-0002-0458-6470
authors.initials: I
authors.lastname: Kulich
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.).
authors.forename: Michal
authors.initials: M
authors.lastname: Hála
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.).
authors.forename: Klára
authors.initials: K
authors.lastname: Aldorfová
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.).
authors.forename: Matyáš
authors.identifier: http://orcid.org/0000-0002-9767-8699
authors.initials: M
authors.lastname: Fendrych
authors.affiliation: Institute of Experimental Botany, Czech Academy of Sciences, 16502 Prague 6, Czech Republic (L.S., N.V., M.H., K.A., M.F., V.Ž.); and lukas.synek@kaust.edu.sa zarsky@ueb.cas.cz.|Department of Experimental Botany, Faculty of Science, Charles University, 12844 Prague 2, Czech Republic (I.K., M.H., K.A., V.Ž.) lukas.synek@kaust.edu.sa zarsky@ueb.cas.cz.
authors.forename: Viktor
authors.identifier: http://orcid.org/0000-0002-5301-0339
authors.initials: V
authors.lastname: Žárský
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D009154:Mutation; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D011058:Pollen / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D053205:Pollen Tube / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D033921:Vesicular Transport Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C000627965:EXO70C2 protein, Arabidopsis; D020033:Protein Isoforms; D033921:Vesicular Transport Proteins; D049452:Green Fluorescent Proteins