title: Two Arabidopsis AGC kinases are critical for the polarized growth of pollen tubes.
abstract: Reproduction of flowering plants requires the growth of pollen tubes to deliver immotile sperm for fertilization. Pollen tube growth resembles that of polarized metazoan cells, in that some molecular mechanisms underlying cell polarization and growth are evolutionarily conserved, including the functions of Rho GTPases and the dynamics of the actin cytoskeleton. However, a role for AGC kinases, crucial signaling mediators in polarized metazoan cells, has yet to be shown in pollen tubes. Here we demonstrate that two Arabidopsis AGC kinases are critical for polarized growth of pollen tubes. AGC1.5 and AGC1.7 are pollen-specific genes expressed during late developmental stages. Pollen tubes of single mutants had no detectable phenotypes during in vitro or in vivo germination, whereas those of double mutants were wider and twisted, due to frequent changes of growth trajectory in vitro. Pollen tubes of the double mutant also had reduced growth and were probably compromised in response to guidance cues in vivo. In the agc1.5 background, downregulation of AGC1.7 using an antisense construct phenocopied the growth defect of double mutant pollen tubes, providing additional support for a redundant function of AGC1.5/1.7 in pollen tube growth. Using the actin marker mouse Talin, we show that pollen tubes of double mutants had relatively unaffected longitudinal actin cables but had ectopic filamentous actin, indicating disturbed control of polarity. Our results demonstrate that AGC1.5 and AGC1.7 are critical components of the internal machinery of the pollen tube leading to polarized growth of pollen tubes.
authors.affiliation: Plant Gene Expression Center, United States Department of Agriculture/Agricultural Research Service, University of California at Berkeley, 800 Buchanan Street, Albany, CA 94710, USA. yan_zhang@berkeley.edu
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Junmin
authors.initials: J
authors.lastname: He
authors.forename: Sheila
authors.initials: S
authors.lastname: McCormick
mesh_terms: D000199:Actins / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D016254:Mutagenesis, Insertional; D009154:Mutation; D053205:Pollen Tube / Q000166:cytology / Q000235:genetics / Q000254:growth & development*; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D018749:RNA, Plant / Q000235:genetics
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; D018749:RNA, Plant; D011494:Protein Kinases