The Search for Components of the Self-incompatibility Signalling Pathway(s) in Brassica napus

Abstract

The Brassica self-incompatibility system is controlled by a multi-allelic S receptor kinase (SRK) gene. Upon contact between self-incompatible pollen and the stigmatic papillae at the surface of the pistil, this receptor kinase is predicted to initiate a signalling pathway in the stigmatic papilla leading to the rejection of the self-incompatible pollen. Several different approaches have been taken to determine the molecular events occurring in the stigmatic papillae upon activation of the self-incompatible response. Examination of cytosolic calcium levels, electrical responses, cytoskeletal organization, and callose deposition in the stigmatic papillae during compatible and incompatible pollinations fail to reveal any responses specific to self-incompatibility. However, the identification of stigmatic proteins which interact with the SRK kinase domain has led to the characterization of a novel protein called ARC1 which appears to be a substrate for the S receptor kinase and is a positive effector of the self-incompatibility response.