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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Actin Dynamics in Papilla Cells of Brassica rapa during Self- and Cross-Pollination^1,[W]

Graduate School of Biological Sciences, Nara Institute of Science and Technology, Ikoma, Nara 630–0101, Japan (M.I., H.S., T.M., M.F., T.E., P.N., H.S., A.I., S.T.); and Research Center for Ultra-High Voltage Electron Microscopy, Osaka University, Suita, Osaka 565–0781, Japan (K.M., A.T.)

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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with journal policy described in the Instructions for Authors (http://www.plantphysiol.org) is: Megumi Iwano (m-iwano{at}bs.naist.jp).

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.106.095273

^* Corresponding author; e-mail m-iwano{at}bs.naist.jp; fax 81–743–72–5459.

Received December 26, 2006; accepted February 17, 2007; published March 2, 2007.

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Peter V. Minorsky
Plant Physiol. 2007 144: 1-2. [Full Text]