Actin dynamics in papilla cells of Brassica rapa during self- and cross-pollination.
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.
Iwano
Megumi
M
Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630-0101, Japan. m-iwano@bs.naist.jp
Shiba
Hiroshi
H
Matoba
Kyoko
K
Miwa
Teruhiko
T
Funato
Miyuki
M
Entani
Tetsuyuki
T
Nakayama
Pulla
P
Shimosato
Hiroko
H
Takaoka
Akio
A
Isogai
Akira
A
Takayama
Seiji
S
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
D000199:Actins; D049452:Green Fluorescent Proteins; D015638:Cytochalasin D