Manipulating Male Sterility

For many crops, it was either impossible or very difficult to generate commercial hybrid seed by conventional means. Hybrid seed is attractive to seed companies because farmers must purchase new seed from them each year, since hybrid varieties do not breed true. It is now possible to engineer male sterility by expression of a ribonuclease gene (barnase) specifically during development of the tapetal layer that nourishes developing pollen grains. Developmental regulation of the ribonuclease (by the TA29 tapetum specific promoter) kills the tapetal cells leading to male sterility. Male sterile plants can be used as the female parent to produce hybrid seed. Fertility can be restored by expression of the barstar gene, which inactivates barnase. This technology can be used to produce hybrids of crops such as maize or sugar beet or canola/rapeseed. It is not possible to produce hybrid canola conventionally and hybrid canola can exhibit hybrid vigour and increased yields. The same basic technology can also be used to induce sterility in transgenic trees, to prevent gene flow via crosspollination.