Me, myself and I. The genetics and molecular biology behind self‐incompatibility and the avoidance of inbreeding in plants

The emergence of sex was a huge leap for evolution. The development of sexual reproduction meant that random mutations were no longer the only source of genetic variety on which selection could act. By mixing up parental alleles, sex essentially put evolution on afterburners; it creates a rich abundance of new varieties, which are the substrate for the process of natural selection and evolution.However, sexual reproduction came with a new set of problems. On the one hand, incest must be avoided, as reproduction between closely related individuals leads to the accumulation of detrimental traits owing to the lack of genetic variety; on the other hand, inter‐species reproduction creates sterile individuals. Animals have thus evolved a range of molecular and behavioural strategies to cope with incest, while at the same time ensuring that they only reproduce with their own kind.Plants have faced the somewhat larger challenge of overcoming their lack of mobility and resulting inability to directly select their mates. They have therefore evolved sexual reproduction that utilizes mobile male gametes—pollen—that must be transmitted to another plant where they fertilize the oocyte, which will develop into a seed (Fig 1). Early plants released their pollen into the air, relying on the wind to carry it away to other plants. But the emergence of flowering plants—angiosperms—refined this process to commandeer insects to transport pollen from one plant to another. Yet, neither strategy solves the problem of incest, as both the wind and insects are likely to carry pollen to a flower from the same plant, or to a very closely related individual.Figure 1. Pollination, fertilization and germination in flowering plants. To overcome their lack of mobility, flowering plants release their male gametes as pollen to be delivered—usually by the wind or insects—to other members of their species. To avoid incest and …