title: MAP18 regulates the direction of pollen tube growth in Arabidopsis by modulating F-actin organization.
abstract: For fertilization to occur in plants, the pollen tube must be guided to enter the ovule via the micropyle. Previous reports have implicated actin filaments, actin binding proteins, and the tip-focused calcium gradient as key contributors to polar growth of pollen tubes; however, the regulation of directional pollen tube growth is largely unknown. We reported previously that Arabidopsis thaliana MICROTUBULE-ASSOCIATED PROTEIN18 (MAP18) contributes to directional cell growth and cortical microtubule organization. The preferential expression of MAP18 in pollen and in pollen tubes suggests that MAP18 also may function in pollen tube growth. In this study, we demonstrate that MAP18 functions in pollen tubes by influencing actin organization, rather than microtubule assembly. In vitro biochemical results indicate that MAP18 exhibits Ca(2+)-dependent filamentous (F)-actin-severing activity. Abnormal expression of MAP18 in map18 and MAP18 OX plants was associated with disorganization of the actin cytoskeleton in the tube apex, resulting in aberrant pollen tube growth patterns and morphologies, inaccurate micropyle targeting, and fewer fertilization events. Experiments with MAP18 mutants created by site-directed mutagenesis suggest that F-actin-severing activity is essential to the effects of MAP18 on pollen tube growth direction. Our study demonstrates that in Arabidopsis, MAP18 guides the direction of pollen tube growth by modulating actin filaments.
authors: State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing 100193, China.
authors: Lei
authors: L
authors: Zhu
authors: Yan
authors: Y
authors: Zhang
authors: Erfang
authors: E
authors: Kang
authors: Qiangyi
authors: Q
authors: Xu
authors: Miaoying
authors: M
authors: Wang
authors: Yue
authors: Y
authors: Rui
authors: Baoquan
authors: B
authors: Liu
authors: Ming
authors: M
authors: Yuan
authors: Ying
authors: Y
authors: Fu
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics / Q000378:metabolism; D000199:Actins / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D053205:Pollen Tube / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D054817:Pollination; D011485:Protein Binding; D012639:Seeds / Q000235:genetics / Q000378:metabolism; D057945:Self-Fertilization
chemical_list: D000199:Actins; D029681:Arabidopsis Proteins; C520841:MAP18 protein, Arabidopsis; D008869:Microtubule-Associated Proteins; D002118:Calcium