Pollen spares all but self

Many plants encourage genetic diversity by preventing self-pollination. Two groups now show that this system works by protecting only an RNase that destroys self. This RNase stops the growth of genetically identical pollen tubes, but RNases that would destroy nonidentical pollen tubes are themselves degraded.

The RNases are made by a part of the S-locus, a huge, intractable stretch of DNA. Although the female-specific product of the S-locus has long been known to be the S-RNase, the male-specific product (made by the pollen tube) has eluded scientists for a decade. It is now identified as a regulator of ubiquitination that seems to sentence all but self S-RNases to degradation.

Through a brute force sequencing approach, Paja Sijacic, Teh-hui Kao (Penn State University), and colleagues found that the petunia pollen S...