We find that many targets of sirenRNAs are AGAMOUS-LIKE transcription factors (AGLs) that become highly upregulated in the hybrid endosperm as well as in maternal Pol IV depleted endosperm, connecting sirenRNA depletion with increased expression of major endosperm regulatory genes. (5/5)

We find that siRNAs accumulating to high levels in the endosperm (sirenRNAs) are strongly depleted in the hybrid, similar to mutants depleted for maternal Pol IV function. (4/5)

The chromatin in hybrid endosperm is highly decondensed and has low CHG and CHH DNA methylation. We observed a similar phenotype in endosperm lacking maternal Pol IV function, suggesting a role of maternal Pol IV-dependent siRNAs in establishing hybridization barriers. (3/5)

Hybridization barriers in Capsella can be bypassed by increasing the ploidy of the maternal parent, suggesting the presence of a maternal dosage sensitive component.(2/5)