A Cysteine-Rich Protein, SpDIR1L, Implicated in S-RNase-Independent Pollen Rejection in the Tomato ( Section ) Clade.

Tomato clade species ( sect. ) display multiple interspecific reproductive barriers (IRBs). Some IRBs conform to the SI x SC rule, which describes unilateral incompatibility (UI) where pollen from SC species is rejected on SI species' pistils, but reciprocal pollinations are successful. However, SC x SC UI also exists, offering opportunities to identify factors that contribute to S-RNase-independent IRBs. For instance, SC LA0716 pistils only permit SC pollen tubes to penetrate to the top third of the pistil, while pollen penetrates to ovaries. We identified candidate LA0716 pistil barrier genes based on expression profiles and published results. CRISPR/Cas9 mutants were created in eight candidate genes, and mutants were assessed for changes in pollen tube growth. Mutants in a gene designated (), which encodes a small cysteine-rich protein, permitted pollen tubes to grow to the bottom third of the style. We show that SpDIR1L protein accumulation correlates with IRB strength and that species with weak or no IRBs toward pollen share a 150 bp deletion in the upstream region of . These results suggest that contributes to an -RNase-independent IRB.