Androgenetic segregation

Finding the right progeny faster

If the target gene and marker gene have been integrated separately in the plant genome (co-transformation), progeny must then be identified which carry the target gene on both chromosomes, but not the marker gene. Since statistically this desired combination of traits is only found in one in sixteen progeny, this can be a laborious process. A new method aims to make it faster and simpler.
Plant breeders require homozygous plants, which carry the target gene on both chromosomes.

Only if the new germ cells (gametes ) all carry the target gene will they produce progeny that all carry the target gene. For this reason, after segregation progeny must be identified, which are marker‑free on both chromosomes and carry the target gene twice.

A new method known as androgenetic segregation is being used to simplify the time-consuming search for these progeny. Transgenic plants in which the target and marker gene are separately integrated (co-transformation) are taken as the starting point.

In each case the germ cells contain only one set of chromosomes. Then comes the clever bit: the scientists intervene during the production of the male germ cells (androgenesis). If the unripe pollen is subjected to stress during androgenesis, the normal development to ripe pollen can be arrested. The set of chromosomes can be replicated either spontaneously or with an artificial trigger. In the right conditions, cells with the duplicated "single" set of chromosomes (double haploid) can be stimulated to divide and regenerate.

The advantage: plants regenerated from these cells have only four possible gene combinations (see diagram) and statistically every fourth plant is marker-free and contains the target gene twice, as desired.

This makes it much quicker to identify the progeny with the desired combination of traits: now every fourth plant instead of every sixteenth plant contains the target gene but not the marker gene. This combination can be identified using PCR and Southern Blot techniques.

More from GMO Safety

• Co-transformation and Segregation: Two genes in, one gene out
• Current SiFo project: Producing marker-gene-free cereal plants using androgenetic segregation; Institute of Plant Genetics and Crop Plant Research, Gatersleben