COPI complex isoforms are required for the early acceptance of compatible pollen grains in Arabidopsis thaliana

The Coat Protein I (COPI) complex is a seven-subunit coatomer complex consisting of the α, β, β', γ, δ, ε, and ζ proteins. In Arabidopsis thaliana, COPI is required for retrograde transport from the Golgi to the endoplasmic reticulum, Golgi maintenance, and cell plate formation. During compatible pollination, vesicle recruitment to the pollen contact point is required for pollen hydration and pollen tube penetration. Here, to identify other aspects of trafficking involved in the acceptance of compatible pollen by stigmatic papillae and to determine their roles in compatible pollination, we characterized knockout lines of several isoforms of the COPI complex, including α1-COP, γ-COP, and ε-COP. Specifically, we characterized pollen grain adherence, pollen tube penetration, and seed set in the mutants. Of the mutant lines examined, α1-cop had the most severe phenotypes, including altered compatible pollen grain adherence and tube germination and reduced seed set, whereas the other lines had milder phenotypes but visibly retarded compatible pollen acceptance. This is the first study demonstrating that COPI complex subunits are required for the acceptance of compatible pollen.