The dynamic nature of apomixis in the angiosperms

Apomixis, the asexual production of seed, is a trait estimated to occur in fewer than 1% of flowering plant species, with an uneven distribution among lineages. In the past decade, targeted research efforts have aimed at clarifying the genetic basis of apomixis, with the goal of engineering or breeding apomictic crops. Recent work suggests a simple genetic basis for apomixis, but it also indicates that natural populations of apomicts are much more complex than is often assumed. For example, in nature, nearly all apomicts that go through a megagametophyte stage (gametophytic apomicts) are polyploid, while their sexual relatives are typically diploid. Although populations have been characterized as obligately sexual or apomictic, it is increasingly clear that many plant populations exhibit some variation in reproductive mode. Many apomicts retain residual sexual function as pollen donors and thus have the potential to spread apomixis via male gametes, thereby increasing the genetic diversity observed within apomictic populations. Here, we summarize our current understanding of the genetic basis and transmission of apomixis. We use insights from previous case studies and models for the spread of asexuality to explore the potential for establishment and spread of apomixis in nature.