Endosperm-based incompatibilities in hybrid monkeyflowers

The sexual endosperm is an angiosperm innovation central to flowering plant reproduction. Genomic interactions between parental alleles control its development and help determine seed viability. These interactions are characterized by genomic imprinting, where expression from certain genes is parent-specific. Unsuccessful imprinting has been linked to failed hybridization between plants of different species or ploidies. Here, we describe an endosperm-based barrier between Mimulus guttatus, a diploid, and M. luteus, an allotetraploid. Hybrid seeds suffer from underdeveloped endosperm, reducing viability, when M. guttatus is the seed parent, and from arrested endosperm and abortion when M. luteus is the seed parent. The two parental species differ in patterns of endosperm DNA methylation, expression dynamics, and their sets of imprinted genes; and transgressive patterns of methylation and expression emerge in their hybrids. The two inherited M. luteus subgenomes, which are genetically dis...