What transgenic plants do

What can transgenic plants do?

Survive harsh conditions (abiotic stress). Plants made to produce more osmolytes (small molecules that hold water in cells), such as the sugars trehalose and fructans and the amino acids betaine and proline, better tolerate drought, salinity and extreme temperatures.

Resist pests (biotic stress). Bt crops carry cry genes from the bacterium Bacillus thuringiensis. Each kind of Cry toxin kills only one group of insects: cryIAc and cryIIAb act on cotton bollworms, cryIAb on corn borers. Useful insects such as butterflies and silkworms are spared. Bt cotton is grown in India; Bt brinjal, maize, rice and tomato also exist. Other GM traits include herbicide tolerance, virus resistance, delayed ripening, and better nutrition: Golden Rice is enriched with vitamin A.

Silencing genes. A gene can be switched off by destroying its mRNA:

• An antisense oligonucleotide binds the target mRNA; the bound mRNA is either destroyed by the enzyme RNase H or simply cannot be read by ribosomes.
• In RNA interference (RNAi), an enzyme called Dicer cuts double-stranded RNA into small pieces; a protein complex, RISC, keeps one strand as a guide and uses it to find and cut the matching mRNA. Tobacco plants made to produce antisense RNA against the roundworm Meloidogyne incognita are protected from it.

Molecular farming. Plants can be used as factories to make vaccine antigens, medicines, bioplastics and enzymes; putting the genes into chloroplasts gives higher yields. Elelyso, made in carrot cells to treat Gaucher's disease, was the first plant-made human medicine approved, in 2012. Lettuce has been made to produce a hepatitis B antigen, and safflower to produce insulin.

Helping the environment. Transgenic sugarcane makes PHB, a biodegradable plastic. Plants carrying the bacterial mercuric reductase gene can detoxify mercury in polluted soil (phytoremediation).