Three types of genes underlying the Gametophyte factor1 locus cause unilateral cross incompatibility in maize

Abstract

AbstractUnilateral cross incompatibility (UCI) occurs between popcorn and dent corn, and represents a critical step towards speciation. It has been reported thatZmGa1P, encoding a pectin methylesterase (PME), is a male determinant of theGa1locus. However, the female determinant and the genetic relationship between male and female determinants at this locus are unclear. Here, we report three different types, a total of seven linked genes underlying theGa1locus, which control UCI phenotype by independently affecting pollen tube growth in both antagonistic and synergistic manners. These include five pollen-expressedPMEgenes (ZmGa1Ps-m), a silk-expressed PME gene (ZmPME3), and another silk-expressed gene (ZmPRP3), encoding a pathogenesis-related (PR) proteins.ZmGa1Ps-mconfer pollen compatibility. Presence ofZmPME3causes silk to reject incompatible pollen.ZmPRP3promotes incompatibility pollen tube growth and thereby breaks the blocking effect ofZmPME3. In addition, evolutionary genomics analyses suggest that the divergence of theGa1locus existed before maize domestication and continued during breeding improvement. The knowledge gained here deepen our understanding of the complex regulation of cross incompatibility.