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CODE RED: Switching to pathogen defence

Scientists at Cambridge used artificial evolution to improve the plant equivalent of antibodies. The research was published in the Proceeding of the National Academy of Sciences late last year.  doi: 10.1073/pnas.1311134110

As plant cells, like plants themselves, are fixed in place unable to move (due to a rather bulky cell wall), they lack the adaptive arm of the immune system found in animals, which is afforded by mobile defender cells. Instead, plants have a highly sophisticated innate immune system.

At the pinnacle of this innate immune system is a class of genes called "Resistance" genes. These Resistance genes are responsible detecting and responding to highly specific and dangerous pathogens. Before their discovery, crop breeders had been unwittingly selecting for these Resistance genes for centuries.

Researchers from the Baulcombe lab have been working on a particular model resistance gene from potato, called Rx, which provides resistance to a virus. In 2006 (doi:10.1073/pnas.0605777103), the lab showed that the recognition spectrum could be altered, creating broad recognition versions of Rx. The new research follows on from this work and shows that the sensitivity of Rx can also be enhanced, by simply targeting a different portion of the gene.

The strategy used for both of these studies was to isolate the gene from the plant, randomly mutagenise it and screen for variants with improved characteristics before finally re-inserting the modified Rx gene back into the plant - hence artificial evolution.

This is similar to a process called "somatic hypermutation" (Wikipedia) which occurs in animals during infection when antibodies with the best recognition capabilities are selected by the body to fight the invading pathogen.

This exciting work could have an impact on the future of agriculture. When asked to comment on this, lead author on the paper, Jake Harris, says "This work is an important proof of concept, showing that we now have the understanding and the ability to modify two of the most significant aspects of Resistance gene function, namely recognition an sensitivity. This may be a useful tool in agriculture as all plants use these same Resistance genes and could prove particularly useful as a means to generate resistance to newly emerging pathogens (Nature.com) for which effective Resistance genes do not currently exist in the wild. However, more work will be required, both politically and in the lab, before these technologies could be employed on a routine basis for use in the field."

This work was carried out in collaboration with researchers at Wageningen University in Holland.

Image shows 3D model of the Rx protein ‘sensitivity’ domains in complex with ATP (yellow)