Functional transfer of the papaver si system into self-compatible a. thaliana and investigating the role of the proteasome in the papaver si response

Abstract

Self-incompatibility is adopted by many flowering plants to prevent inbreeding, and is controlled by a multi-allelic $S$-locus. In $Papaver$ $rhoeas$, the pistil $S$-determinant is PrsS (a small secreted protein); the pollen $S$-determinant is PrpS (a novel transmembrane protein). Cognate PrpS-PrsS interaction induces DEVDase-mediated programmed cell death of incompatible pollen. Here, we examined the role of proteasome during the $Papaver$ SI response and showed that the proteasome is a target of the $Papaver$ SI response, and is distinct from the SI-induced DEVDase activity. Our main focus here is translational work, attempting to move the Papaver SI system into $A$. $thaliana$. We previously demonstrated that PrpS:GFP expressed in $A$. $thaliana$ pollen was functional $in$ $vitro$. Here, we expressed the female $S$-determinant, PrsS, in $A$. $thaliana$ and investigated function $in$ $vivo$. We present data demonstrating that transgenic A. thaliana stigmas expressing PrsS pollinated with $A$. $thaliana$ pollen expressing PrpS:GFP inhibited pollen tube growth in an S-specific manner, and virtually no seed was set. Transformation of both $PrpS$$:$$GFP$ and $PrsS$ into $A$. $thaliana$ generated self-incompatible plants that set no self-seed. This demonstrates that transfer of the $Papaver$ SI system into a highly diverged self-compatible species can result in a fully functional SI system