title: Actin dynamics in papilla cells of Brassica rapa during self- and cross-pollination.
abstract: The self-incompatibility system of the plant species Brassica is controlled by the S-locus, which contains S-RECEPTOR KINASE (SRK) and S-LOCUS PROTEIN11 (SP11). SP11 binding to SRK induces SRK autophosphorylation and initiates a signaling cascade leading to the rejection of self pollen. However, the mechanism controlling hydration and germination arrest during self-pollination is unclear. In this study, we examined the role of actin, a key cytoskeletal component regulating the transport system for hydration and germination in the papilla cell during pollination. Using rhodamine-phalloidin staining, we showed that cross-pollination induced actin polymerization, whereas self-pollination induced actin reorganization and likely depolymerization. By monitoring transiently expressed green fluorescent protein fused to the actin-binding domain of mouse talin, we observed the concentration of actin bundles at the cross-pollen attachment site and actin reorganization and likely depolymerization at the self-pollen attachment site; the results correspond to those obtained by rhodamine-phalloidin staining. We further showed that the coat of self pollen is sufficient to mediate this response. The actin-depolymerizing drug cytochalasin D significantly inhibited pollen hydration and germination during cross-pollination, further emphasizing a role for actin in these processes. Additionally, three-dimensional electron microscopic tomography revealed the close association of the actin cytoskeleton with an apical vacuole network. Self-pollination disrupted the vacuole network, whereas cross-pollination led to vacuolar rearrangements toward the site of pollen attachment. Taken together, our data suggest that self- and cross-pollination differentially affect the dynamics of the actin cytoskeleton, leading to changes in vacuolar structure associated with hydration and germination.
authors.affiliation: Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0101, Japan. m-iwano@bs.naist.jp
authors.forename: Megumi
authors.initials: M
authors.lastname: Iwano
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Shiba
authors.forename: Kyoko
authors.initials: K
authors.lastname: Matoba
authors.forename: Teruhiko
authors.initials: T
authors.lastname: Miwa
authors.forename: Miyuki
authors.initials: M
authors.lastname: Funato
authors.forename: Tetsuyuki
authors.initials: T
authors.lastname: Entani
authors.forename: Pulla
authors.initials: P
authors.lastname: Nakayama
authors.forename: Hiroko
authors.initials: H
authors.lastname: Shimosato
authors.forename: Akio
authors.initials: A
authors.lastname: Takaoka
authors.forename: Akira
authors.initials: A
authors.lastname: Isogai
authors.forename: Seiji
authors.initials: S
authors.lastname: Takayama
mesh_terms: D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D000199:Actins / Q000502:physiology*; D029741:Brassica rapa / Q000378:metabolism* / Q000502:physiology / Q000648:ultrastructure; D015638:Cytochalasin D / Q000494:pharmacology; D018525:Germination; D049452:Green Fluorescent Proteins / Q000032:analysis; D012098:Reproduction / Q000502:physiology; D014617:Vacuoles / Q000378:metabolism / Q000648:ultrastructure
chemical_list: D000199:Actins; D049452:Green Fluorescent Proteins; D015638:Cytochalasin D