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Bioscience in brief

New plant technologies

What is gene stacking?

Gene stacking – also known as gene pyramiding – is the process of including more than one transgenic event in one plant to produce stacked traits, stacked transformation events, or a stacked genetically modified organisms (GMO).

The cultivation of stacked GMOs has risen rapidly since they were first approved, and to date they were grown on 51 million ha in 2014, about a quarter of the total area under GM crops worldwide, and are set to become increasingly common.

SOME EXAMPLES OF STACKED GMOs:

  • Maize with combined resistance to shoot and root insect pests and with tolerance to herbicide.

New plant technologies - What is Gene Stacking?Corn borers hiding in the tassel (maize male flowers): this is one of the pests to which GM maize is resistant.

  • Cotton containing two different genes for resistance to cotton bollworm.

Cotton damaged by a cotton bollworm. More than 80 per cent of the cotton grown worldwide is GM Bt cotton with resistance to cotton bollworm.

Plants possess the machinery to synthesise β-carotene, the precursor of vitamin A. While this machinery is fully active in leaves, parts of it are turned off in grain. By adding only two genes, a plant phytoene synthase (psy) and a bacterial phytoene desaturase (crt I), the pathway is turned back on and β-carotene consequently accumulates in the grain. Golden Rice is still pending regulatory approval.

  • Nematode-resistant bananas and plantains.

These are currently undergoing field trials in Uganda. The parasitic worms colonise the roots, impairing the absorption of water and nutrients and causing plants to topple in storms. Nematode infection causes loses between a third and a half of total production, and although these pests can be controlled chemically, nematicides are often too expensive for smallholder farmers, and they are toxic.

There are two ways to control nematodes using a GM approach: one is by inhibiting their digestion by introducing in bananas a small protein from maize; the second is by reducing infection of the root by nematodes via small, non-lethal synthetic peptides (peptides are molecules made by the same building blocks as proteins, but smaller in size). Transgenic lines can produce twice as much as susceptible lines, and double transgenic are also being tested to determine their combined effect on the durability of resistance. This approach could support the future food security of 70 million, mainly poor African smallholder farmers, who rely on plantain as a staple food.

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