Seed Development in Interploidy Hybrids

Hybridization between plants of the same or different species can have dramatic effects on seed size and survival. Postzygotic hybridization barriers may prevent the development of viable seeds or fertile hybrids, and can arise within a single species as a result of polyploidization, resulting in genetic isolation and potentially sympatric speciation. Dramatic growth-related changes in endosperm development, principally cellularization and proliferation, frequently account for seed failure following hybridization between polyploids and their diploid progenitors. Misexpression of key transcription factors controlled by a PcG complex that contains factors subject to genomic imprinting explains this behaviour in Arabidopsis thaliana. Further insights into the origin and nature of postzygotic hybridization barriers are being provided by analysis of the Columbia ecotype of A. thaliana where (2x × 4x) crosses show high-frequency seed abortion. Loss of the flavonoid biosynthesis pathway activity in the integuments strongly mitigates this lethality implying a role for the seed coat in regulating endosperm cellularization.