GLOBAL: A plant's eye view of shade avoidance

The world of a plant can be a stressful place. Many plants constantly compete with their neighbours for light by elongating to try and get out of their shade and in crops this elongation can dramatically reduce the yield so is a major limiting factor in how densely a farmer can plant a crop.

Scientists at the Centre for Research in Agricultural Genomics in Barcelona and at Royal Holloway, University of London, have been studying the effects of shade avoidance. They hope eventually to impede this response and therefore increase planting density.

Using a fast-growing 'model plant', the scientists searched for individuals which showed a loss of this response. To do this, they inserted a bioluminescent 'reporter' to follow the activity of a shade-responsive gene in living plants.

They simulated shade by adding extra far red light and found that they could observe the plant glowing within as little as 20 minutes after the treatment. Using this system they were able to screen through thousands of plants to identify a number of plant strains they called 'dracula strains' which show no avoidance of shade.

Dr Paul Devlin from the school of biological sciences at Royal Holloway explained: "Shade avoidance is a major limiting factor in how densely a farmer can plant a crop. If plants are too close together then the shade avoidance response kicks in and they become too tall and spindly to produce a good yield.

"The new dracula strains we've identified in this model plant show a greatly reduced response and we hope that, ultimately, these plants can give us clues as to how we might also attenuate this response in crops."

The study was supported by The Royal Society and the Spanish CSIC; the University of London Central Research Fund and the Generalitat de Catalunya and the Ministerio de Ciencia e Innovación in Spain. A paper describing the research was published in the 11 March issue of the Journal of Experimental Botany.

Meantime, Australian scientists have uncovered a rare insight into a war between genes to control the sex of a plant. The researchers, from the ARC Centre of Excellence in Plant Energy Biology and the school of biomedical sciences at the University of Western Australia, have described the evolution of a 'restorer to fertility' (Rf) gene that influences sex determination.

The findings, published in the Proceedings of the National Academy of Sciences, have important implications for agricultural science and medicine.

Plant cells, like human cells, contain tiny mitochondria that produce energy for the cell. Mitochondria are thought to be descended from bacteria that entered the cell over two billion years ago and contain their own genes. Some of these genes produce proteins which can turn a hermaphrodite plant into a female by preventing the male parts of the flower from forming.

Researcher Dr Sota Fujii said mitochondria were more likely to pass on their genetic information when the plant was female. But plants have a defence mechanism and, in their paper, Fujii and co-workers describe the evolution of Rf genes which produce proteins that block the action of the mitochondrial male-sterility inducing genes by binding to the RNA they produce.

The finding demonstrates a 'civil war' between the nucleus and the mitochondria over the determination of the sex of the plant that has been going on for millions of years.

Chief Investigator Professor Ian Small said: "Our analysis of the evolution of Rf genes not only strongly supports their role in sex determination, it also gives us clues as to exactly how they work. The ability to silence destructive products in the cell has obvious possibilities in agricultural science and in medicine. The potential to control the sex of a plant is also important in commercial crop breeding."