HT proteins contribute to S‐ RN ase‐independent pollen rejection in Solanum

Summary Plants have mechanisms to recognize and reject pollen from other species. Although widespread, these mechanisms are less well understood than the self‐incompatibility ( SI ) mechanisms plants use to reject pollen from close relatives. Previous studies have shown that some interspecific reproductive barriers ( IRB s) are related to SI in the Solanaceae. For example, the pistil SI proteins S‐ RN ase and HT protein function in a pistil‐side IRB that causes rejection of pollen from self‐compatible ( SC ) red/orange‐fruited species in the tomato clade. However, S‐ RN ase‐independent IRB s also clearly contribute to rejecting pollen from these species. We investigated S‐ RN ase‐independent rejection of Solanum lycopersicum pollen by SC Solanum pennellii LA 0716, SC . Solanum habrochaites LA 0407, and SC Solanum arcanum LA 2157, which lack functional S‐ RN ase expression. We found that all three accessions express HT proteins, which previously had been known to function only in conjunction with S‐ RN ase, and then used RNA i to test whether they also function in S‐ RN ase‐independent pollen rejection. Suppressing HT expression in SC S. pennellii LA 0716 allows S. lycopersicum pollen tubes to penetrate farther into the pistil in HT suppressed plants, but not to reach the ovary. In contrast, suppressing HT expression in SC . Solanum habrochaites LA 0407 and in SC S. arcanum LA 2157 allows S. lycopersicum pollen tubes to penetrate to the ovary and produce hybrids that, otherwise, would be difficult to obtain. Thus, HT proteins are implicated in both S‐ RN ase‐dependent and S‐ RN ase‐independent pollen rejection. The results support the view that overall compatibility results from multiple pollen–pistil interactions with additive effects.