Summary of the stigmatic papillar responses to compatible and self-incompatible pollen.

<p>(<b>A</b>) Percentage of samples with the main ultrastructural features observed in the TEM images. Corresponding TEM images are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084286#pone-0084286-g001" target="_blank">Figures 1</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084286#pone-0084286-g004" target="_blank">4</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084286#pone-0084286-g007" target="_blank">7</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084286#pone-0084286-g009" target="_blank">9</a>. Abbreviations: Un = unpollinated; MVBs = multivesicular bodies; ABs = autophagic bodies; PM = plasma membrane. (<b>B-D</b>) Models for compatible pollen responses (based on this study and cited references). Under the compatible pollen contact site, an unknown basal pollen recognition pathway is activated in the stigmatic papilla. This leads to the assembly of the exocyst complex with Exo70A1 and plasma membrane docking of vesicles in <i>Arabidopsis</i> species (B, C) or MVBs in <i>B. napus</i> (D). Following vesicle/MVB fusion to the plasma membrane by SNAREs, unknown cargo are released to facilitate water release for pollen hydration and cell wall expansion for pollen tube entry (pollen is accepted). (<b>E, F</b>) Models for loss of Exo70A1 function in the stigmatic papilla (based on this study and cited references). Disrupting <i>Exo70A1</i> expression prevents plasma membrane docking of vesicles in <i>A. thaliana exo70A1-1</i> (E) or MVBs in <i>B. napus Exo70A1</i> RNAi (F). Consequently, vesicles/MVBs accumulate in the cytoplasm; cargo needed for accepting the compatible pollen are not delivered to the plasma membrane; and this leads to pollen rejection. (<b>G, H</b>) Models for self-incompatible pollen responses (based on this study and cited references). With self-incompatible pollen, the self-incompatibility pathway is activated in the stigmatic papilla and overrides the basal pollen recognition pathway by inhibiting Exo70A1 and vesicle/MVB docking. The vesicles in <i>A. lyrata</i> (G) or MVBs in <i>B. napus</i> (H) are redirected to the vacuole via autophagy for degradation. Consequently, pollen hydration and pollen tube penetration are prevented (self-pollen is rejected). (<b>I</b>) Model for the partial breakdown of self-incompatibility through the expression of <i>RFP:Exo70A1</i> in <i>B. napus </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084286#pone.0084286-Samuel1" target="_blank">[17]</a>. MVBs are able to dock at the plasma membrane despite the activation of the self-incompatibility pathway, and this leads to pollen acceptance (pollen hydration and pollen tube entry occur <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0084286#pone.0084286-Samuel1" target="_blank">[17]</a>. RFP:Exo70A1 may potentially cause this phenotype through increased Exo70A1 levels or by interference with the ARC1 interaction.