Nature Biotechnology pp 453 - 456

Biotechnologists have come up with a way to make sex deadly for medflies, resulting in a strategy which thwarts an insect pest that currently causes millions of dollars of crop losses in the US and elsewhere every year. In the April issue of Nature Biotechnology, researchers in the UK use genetic engineering to create male strains of the Mediterranean fruit fly or medfly (Ceratitis capitata) that cannot produce viable offspring when they mate with the natural population of female medflies.

Luke Alphey and colleagues describe a genetic system for controlling medflies that takes advantage of a protein, the tetracycline-repressible transactivator (tTA), which interacts with the antibiotic tetracycline. In the presence of tetracycline, tTA is expressed at low levels and is innocuous to medflies; when tetracycline is withdrawn, however, tTA is expressed to such high levels it causes causes severe growth impairment or death in these insects. By introducing a construct harboring tTA into medflies using transgenic techniques, the researchers produce male medflies that mate with wild females to produce eggs that are incapable of developing into adult flies.

These transgenic medflies complement current sterile insect techniques that use radiation to mutagenize male medflies, which can then be released to mate with the natural population of medfly females to control medfly infestations. Unlike the radiation method, however, which often induces changes that make mutant males less attractive than natural males to females, the genetic approach produces sterile males that are more likely to be as attractive. The Mediterranean fruit fly is one of the world's most important agricultural pest insect, attacking more than 250 kinds of fruits, nuts and vegetables.

Nature Biotechnology pp 482 - 487

An improved version of Golden Rice, rich in pro-vitamin A, is described in the April issue of Nature Biotechnology. A team of industry scientists in the UK and USA has produced an improved version of 'Golden Rice', which contains significantly elevated levels of beta-carotene (pro-vitamin A) — work that could bring efforts to develop rice strains to help combat dietary vitamin A deficiency closer to reality.

Dietary vitamin A deficiency affects over 250 million people around the globe and can result in blindness and a depressed immune system. Golden Rice 2 accumulates more than 20 times the amount of beta-carotene produced in the original Golden Rice, developed five years ago. Rachel Drake and colleagues engineered the new strain following methodical screening and testing of alternative versions of phytoene synthase — the first enzyme in the beta-carotene pathway — to find the one that produced the most beta-carotene. Among all the enzymes screened, a phytoene synthase from maize gave the best results. The new version of Golden Rice containing the maize enzyme is an excellent starting point for breeding new varieties of rice rich in beta-carotene.

The original Golden Rice, although a valuable first step, was soon recognized to contain insufficient levels of beta-carotene in its grains to allow practical implementation in the field. Golden Rice 2, however, has the potential to provide about 50% of the required daily allowance of vitamin A for children, although this depends on overall diet composition — in particular the amount of dietary oils consumed together with it.

The company developing the new rice strain supports the Humanitarian Project for Golden Rice and intends to donate the strain for further research and development through a research license.

Nature Biotechnology pp 445 - 451

Scientists have generated dairy cows with enhanced resistance to mastitis, an infection of cows' udders that costs the US dairy industry over $2 billion every year through lost productivity. As described in April's Nature Biotechnology, the cows carry a gene that specifically protects them from the bacterium Staphyolococcus aureus, a major cause of mastitis.

Mastitis is a painful infection of the udder that causes inflammation and swelling. Estimates suggest that over one-third of dairy cows in the UK herd suffer from mastitis. The disease is difficult to cure with antibiotics and is often controlled by killing chronically infected cows. Robert Wall and colleagues reasoned that cows expressing an antibacterial protein, lysostaphin, in their mammary gland would be better equipped to fight off infection. Sure enough, when challenged with Stapyhlococcus aureus, cows carrying the lysostaphin gene proved more resistant to mastitis.

Although lysostaphin does not kill all mastitis-causing bacteria, these results suggest that it might be possible to control other harmful bacteria in dairy cattle with different antibacterial genes.