African scientists have uncovered how one of the world’s most economically devastating crop diseases emerged, and hope to genetically engineer disease resistant crops using the information. Researchers from the University of Cape Town (UCT), South Africa, compared the genetic sequence of the virulent maize streak virus (MSV) with ten less harmful strains of the virus from across the continent, which infect other grass food crops such as wheat and oats.

“We found that two relatively mild grass viruses had merged through genetic recombination,” said UCT researcher Dr. Arvind Varsani. This merger resulted in an ancestral MSV far more potent than its parents, which moved into maize before spreading rapidly across the continent. The researchers think that this occurred approximately a century ago, just when commercial agriculture was replacing subsistence farming and maize started to overshadow indigenous crops in Africa. “Our results mean that DNA viruses are evolving faster than was thought. This rapid mutation increases the possibility of new plant viruses emerging,” said Dr. Varsani.

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Maize (corn) – the world’s number one feed grain and a staple food for many – does not tolerate cold well. If maize’s intolerance of low temperatures could be overcome, then the length of the growing season and yield could be increased at present sites of cultivation and its range extended into colder regions. Researchers from the Department of Crop Sciences and the Institute of Genomic Biology at the University of Illinois, the United States, may have made a breakthrough on this front.

Plants can be divided into two groups based on their strategy for harvesting light energy: C4 and C3. The C4 groups include many of the most agriculturally productive plants known, such as maize, sorghum and sugar cane. All other major crops, including wheat and rice, are C3. The C4 plants differ from the C3s by the addition of four extra chemical steps, which make these plants more efficient in converting sunlight energy into plant matter. Until recently, the higher productivity achieved by C4 species was thought to be possible only in warm environments. Recently a wild C4 grass related to maize, Miscanthus x giganteus, has been found to be highly productive in cold climates. The Illinois researchers set about trying to discover the basis of this difference, focusing on the four extra chemical reactions that separate C4 from C3 plants.

Each of the four reactions is catalysed by a protein or enzyme. The enzyme for one of these steps, Pyruvate Phosphate Dikinase (PPDK) is made up of two parts. At low temperature, these parts have been observed to fall apart, differing from the other three C4-specific enzymes. The researchers examined the DNA sequence of the gene coding for this enzyme in both plants, but could find no difference, nor could they see any difference in the behaviour of the enzyme in the test tube. However, they noticed that when maize leaves were placed in the cold, PPDK slowly disappeared in parallel with the decline in the ability of the leaves to take up carbon dioxide in photosynthesis. When Miscanthus leaves were placed in the cold, they made more PPDK and as they did so, the leaves became able to maintain photosynthesis in the cold conditions.
The researchers cloned the gene for PPDK from both maize and Miscanthus into a bacterium, enabling the isolation of large quantities of this enzyme. They discovered that, as the enzyme was concentrated, it became resistant to cold, thus the difference between the two plants was not the structure of the protein components but rather the amount of protein present. The findings suggest that modifying maize to synthesize more PPDK during cold weather could allow it to be cultivated in colder climates and be productive for more months of the year in its current locations.

Source: www.genengnews.com