Nature Biotechnology pp 466 - 469 and pp 417 - 418

Although at least half of the world's population depends on rice for nourishment, rice growth and yield is poor in the iron—deficient alkaline soils of many of the world's arid regions. Researchers in Japan have addressed this problem by engineering rice plants that are more efficient at using available iron, resulting in enhanced growth and yield of rice in alkaline soils.

Iron, nitrogen, and phosphorus are the three nutrients that most commonly limit plant growth. When grown in alkaline soil, many of the grasses grown as food crops—rice, corn, and barley, for example—release mugineic acids such as deoxymugineic acid (DMA), a natural iron chelator that solubilizes iron for uptake by binding and ferrying it across the root plasma membrane. Michiko Takahashi and colleagues proposed that rice is particularly vulnerable to iron deficiency because it produces only miniscule amounts of DMA.

To test their hypothesis, they introduced into rice two barley genes encoding enzymes that catalyze DMA biosynthesis. The resulting transgenic rice plants pumped out larger amounts of DMA than control plants when grown in iron-deficient soil. Moreover, the engineered plants also showed better tolerance for low-iron conditions and yielded more than four times as much grain as controls.

The next step is to target other vulnerable food crops, such as maize and sorghum.

Nature Biotechnology pp 434 - 439 and pp 413 - 414

About one-third of mutations associated with human diseases are nonsense mutations, which cause disease by preventing functional proteins from being made. But so far a method of finding them has remained elusive. In this issue Erick Noensie and Harry Dietz describe a completely new approach to DNA diagnostics that focuses on the type of mutation rather than the type of gene underlying disease.

Genes are first transcribed into messenger RNA transcripts, which are then translated into proteins. Nonsense mutations prematurely halt translation—something that can result in truncated proteins. The accumulation of such deleterious proteins could wreak havoc on normal cell function, but is controlled by the nonsense-mediated mRNA decay (NMD) pathway, which rapidly degrades transcripts containing nonsense mutations. However, the loss of proteins that perform important cellular functions can contribute to diseases such as cancer.

To identify genes containing nonsense mutations, Noensie and Dietz first inactivated the NMD pathway in cells using a drug that stabilized the mutant transcripts. Then they used DNA arrays to identify transcripts that increased in abundance. Taking into account measurements from controls, they detected the previously characterized nonsense mutations in the top 1% of candidates. Combining the strategy with other biological information may help narrow the search for elusive disease-related genes.

Nature Biotechnology pp 470 - 474

The day when eating pizza is considered part of a healthy lifestyle may not be too far away: Scientists have developed a "healthier" tomato that could prove particularly useful in decreasing risk for cardiovascular disease.

Antioxidant chemicals called "flavonols" are thought to protect against heart disease, slow cellular aging, help combat inflammation, and slow the growth of certain cancer cells. Although these compounds exist naturally in tomatoes, the levels are much lower than they are in such foods as onions and tea.

Martine Verhoeyen and colleagues observed that the rate of flavonol biosynthesis is limited by the enzyme, chalcone isomerase (CHI). By inserting a gene that encodes for CHI taken from Petunia plants, which have high levels of flavonols in their reproductive structures, they engineered tomatoes with skin that had up to a 78-fold increase in flavonol levels—an amount in line with that of onions, and a trait that was inherited over four subsequent generations. Moreover, taste was not affected and 65% of the beneficial compounds were retained when the tomatoes were processed into paste, suggesting that this research could lead to the production of tomato-based products with increased health benefits.

Nature Biotechnology pp 429 - 433 and pp 415 - 416

Pollution of waterways with phosphorus derived from intensive animal agriculture is becoming a worrisome environmental threat. But now, research suggests that farm animals could be produced that generate less phosphorus, potentially creating a "cleaner" animal industry.

Because livestock cannot digest the organic phosphorus found naturally in grain, inorganic phosphorus is often added to animal feed to promote optimal growth. But when excess phosphorus in animal manure enters streams and lakes, it stimulates algal blooms that kill fish and other aquatic life. One solution is to fortify animal diets with phytase, an enzyme that allows animals to metabolize naturally occurring organic phosphorus. This environment-friendly approach can eliminate the need for inorganic phosphorus supplementation and reduce the phosphorus content of animal manure. However, phytase is too costly for widespread use, and the enzyme tends to degrade during feed production and storage.

To overcome these problems, Cecil Forsberg and his collaborators set out to produce phytase directly in an animal's digestive tract. Testing the approach in mice, they showed that expressing a bacterial phytase gene in the animal's salivary glands reduced fecal phosphorus by about 11% compared with control mice that did not receive the gene. The researchers are optimistic that their strategy can be applied to farm animals and are currently conducting similar studies in pigs.