The Lateral suppressor technology

There are several reasons, why in many crop plants the formation of side-shoots is a major drawback for crop production:

• Side-shoots act as sink organs and reduce the yield on the main stem.

• Side-shoots are a major impediment for mechanical harvesting.

• Side-shoots reduce the quality of the harvested product (e.g. tobacco, canola).

For these reasons breeders have tried for decades to produce monostem varieties. These attempts were successful in a few crop species (e.g. sunflower), however, in many other species, for which the monostem character would also be desired (e.g. tomato, tobacco), this trait could not be introduced into high yielding lines

In some cases alternative techniques are in use to obtain plants with monostem architecture:

• Side-shoots are manually removed from greenhouse grown tomato plants.

• In tobacco, outgrowth of side-shoots is blocked by the application of chemicals.

These practices account for a high percentage of the production costs, add considerably to the spread of the diseases (tomato) or cause major concerns with respect to product safety and environmental pollution (tobacco).

In tomato breeders have used the lateral suppressor (ls) mutant to introduce the monostem character into breeding lines. However, it turned out that the desired trait was always linked to a severe reduction in fruit set and, therefore, not acceptable for crop production. Following the isolation of the Ls gene one of GreenTecs associates succeeded to disconnect the two traits resulting in tomato plants with a monostem architecture but a normal fruit set. Several transgenic lines show a strong reduction in the number of side-shoots, the strongest being indistinguishable from the lateral suppressor mutant. In contrast, flower and inflorescence morphology as well as fruit set in these lines are comparable to the parent line (cv. Moneymaker). Phenotypes proved to be stable for at least three generations.

Left: Wild Type, Right: Lateral Suppressor Mutant In Tobacco, inflorescences are cut off from flowering plants, because they act as sink organs and reduce the quality of the tobacco leaves. The following outgrowth of side-shoots is presently being controlled by the application of chemicals (sucher control). This treatment causes environmental concerns and affects the quality of tobacco leaves. Using the Lateral suppressor technology it will be possible to inhibit the formation of side-shoots of all leaf axils.

Arabidopsis thaliana plants with reduced Ls levels are also available. They show properties similar to the described tomato plants, a strong reduction in lateral shoot formation during vegetative development, and normal shoot branching during inflorescence development combined with normal seed set. Canola and rape seed, two close relatives of Arabidopsis, are good candidates for the use of the Lateral suppressor technology, because both display branching patterns similar to Arabidopsis. In these plants, late flowering side-shoots are the cause of contaminations of harvested grains with immature green seeds, which can be up to 20%. Anti-nutritional substances from immature seeds have to be extracted before consumption increasing costs and reducing the nutritional value of the products. With the help of the Lateral suppressor technology it will be possible to inhibit the development of late growing side-shoots leading to a reduction in the costs of oil production.