Science 350, 684–687 (2015)

Plants have evolved many ways to avoid self-fertilization — including a number of different self-incompatibility systems, which recognize genetically similar pollen and prevent its growth. Now Zongcheng Lin and colleagues working at the University of Birmingham, UK, have demonstrated that the self-incompatibility mechanism from one group of plants can be functional in another.

The self-incompatibility system of field poppies (Papaver rhoeas) has two main components — a pollen protein, PrpS, and a signal protein, PrsS, produced by the stigma — encoded by closely linked genes within the S locus. When PrpS recognizes PrsS of its own type, it triggers a cell death program within the pollen to abort pollination. But if PrsS does not match, ‘self’ recognition does not occur and pollination can proceed. Lin and colleagues engineered the normally self-fertile Arabidopsis thaliana to express the two poppy genes in pollen and pistils, respectively, creating plants that rejected their own pollen while allowing fertilization by pollen that either does not express PrpS or expresses PrpS of a different class.

It is remarkable that so few genes are needed to implement the poppy self-incompatibility system in Arabidopsis, as these two plants diverged from a common ancestor around 140 million years ago. Similar engineering might be a route to ensure outcrossing in crop breeding.