XVI International Botanical Congess

In the Brassica self-incompatibility response, self pollen is rejected through a mechanism involving the S-receptor kinase (SRK). Since little is known about the signaling pathway activated by SRK, the yeast two-hybrid system was used to isolate potential SRK substrates. Three different clones were isolated which show specific interactions with the SRK kinase domain. THL1 and THL2 belong to the thioredoxin h family and while they bind specifically to the SRK kinase domain, the interaction is not phosphorylation-dependent. The third clone, ARC1, is a novel plant protein with arm repeats in the C-terminal region which mediate a phosphorylation-dependent interaction with the SRK kinase domain. In addition, ARC1 expression is localized to the stigma, the site of the self- incompatibility response.