MJ 2-3 - Pollen Acceptance or Rejection: Cellular regulation of mate selection in the Brassicaceae
Sunday, July 15
10:00 AM - 10:30 AM
In the Brassicaceae (e.g. Brassica and Arabidopsis sp.), the regulation of pollen-pistil interactions and fertility begins rapidly after pollen grains have landed on the stigmatic papillae at the top of the pistil. The pollen grains which carry the sperm cells are in a desiccated state for dispersal, and so, the first step in this process is for the pollen grains to become hydrated for germination. The water for hydration comes from the stigmatic papilla but is only released when the pollen grain is recognized as compatible. This recognition event is facilitated by recognition factors on the pollen surface that are mixed into the pollen-papillar interface. Following hydration, a pollen tube emerges and penetrates the stigmatic surface to begin its journey down the pistil to deliver the sperm cells to an ovule for fertilization. One of the key outstanding questions is how compatible pollen grains are recognized and what cellular events are activated in stigmatic papillae for pollen hydration and pollen tube entry into the stigma (the ‘basal compatible pollen response pathway’). We have identified vesicle trafficking as a component of this pathway and are now investigating a number candidate signalling proteins for initiating this pathway. Interrelated to compatible pollen recognition is the self-incompatibility system present in a number of Brassicaceae species where self-pollen is rejected to prevent inbreeding. A second research direction is to better understand the self-incompatibility pathway and how it overrides the basal compatible responses in the stigmatic papillae. The key regulators of self-incompatibility are well-known, the pollen SP11/SCR ligand and the stigma S Receptor Kinase, and some downstream signalling events have been identified. We continue to investigate these cellular responses to understand how they contribute to the rejection of self-pollen.