Molecular, Cell, Development (MCD) Seminar Series - McMaster University
2008-09 || 2009-10 || 2010-11 || 2011-12 || 2012-13

Molecular, Cell, Development (MCD) SEMINAR SERIES
Department of Biology

Speaker: Dr. Daphne Goring

Date: Friday 11th, January, 2013
Time: 12 noon
Location: HSC 1A3

Title: Signaling events in the pistil initiated by pollen contact in the mustard family (Brassicaceae): Pollen acceptance or rejection?

Many flowering plants possess self-incompatibility systems which prevent inbreeding by rejecting “self” pollen, and this response occurs following interactions between the pollen (male gametes) and the pistil (female part of the plant). In Brassica, the self-incompatibility response is induced when the polymorphic SCR/SP11 ligand on the ‘self’ pollen grain binds to the matching S Receptor Kinase (SRK) on the stigmatic papilla (at the surface of the pistil). This ligand-receptor interaction triggers a signal cascade that is proposed to activate the ARC1 E3 ubiquitin ligase. This, in turn, is proposed to trigger pollen rejection by ARC1’s activity promoting the inhibition of factors required for compatible pollen acceptance. Exo70A1 is one such ARC1 target that we have uncovered in this system. Exo70A1 is required in the pistil for the early stages of compatible pollen hydration and pollen tube penetration into the pistil. In our model, we hypothesize that Exo70A1 functions, as part of the exocyst complex, to tether secretory vesicles to the pistil plasma membrane under the pollen contact site. This is thought to result in water transfer to the pollen grain for hydration as well as the expansion of the papillar cell wall to promote pollen tube penetration for the subsequent fertilization. To test this model, we are examining the other subunits of the exocyst complex and using transmission electron microscope to observe the presence or absence of secretory vesicles, following compatible or self-incompatible pollinations. As well, we have investigated if the role of ARC1 is evolutionarily conserved in regulating pollen rejection in other naturally self-incompatibility systems in the Brassicaceae. From this research, the cellular mechanisms in the Brassicaceae that regulate whether pollen is accepted or rejected are being better understood.