Researchers from The Australian National University have discovered a new cellular communication process used by plants to respond to drought.

The team, led by Dr Gonzalo Estavillo and Professor Barry Pogson in the ANU Research School of Biology, examined a small, rapid-growing plant called, a relative of canola.

The researchers discovered evidence of a process called retrograde signalling – where chemical signals move between different cellular compartments in the plant. The movement of these signals switches on a defense mechanism which could help plants cope with drought conditions.

“The chloroplast is the cellular subunit in a plant that converts light into sugars and is the most expensive cellular compartment to run,” said Dr Estavillo. “Thus, the nucleus, or control centre of the cell, needs to ensure efficient assembly and function of the chloroplast and that requires communication between the two compartments.

“The chloroplast is also an environmental sensor of stress and this is what initiates the response. In the presence of stress, the chloroplast communicates with the nucleus to change the activity of thousands of genes, impacting on photosynthesis and growth.

“We have evidence that a chemical called PAP acts as a signal between the plant’s chloroplast and nucleus. This type of signalling or ‘cross-talk’ between cellular compartments also occurs in animals, using other chemicals.

“Plants that have more PAP are more tolerant to drought. Our results support the notion that the movement of PAP from the chloroplast to the nucleus signals to the plant that it is suffering from drought conditions, initiating changes in gene activity to cope with drought stress.”

Dr Estavillo added that this process is helped when a protein called SAL1 is removed from the plant.

“In Arabidopsis the SAL1 protein usually degrades the chemical PAP. However, we have knocked SAL1 out of our mutant plants,” said Dr Estavillo. “This led to higher levels of PAP in the mutant, which we previously reported to be drought tolerant.

“More importantly, we also observed that PAP accumulated in normal plants during drought. Our hypothesis is that PAP accumulation allows drought-adaptive genes to be freely expressed.”

The breakthrough could potentially establish natural forms of drought resistance in food crops.

“The SAL1 mutation has the advantage of facilitating less controversial solutions to the enhancement of food crops,” said Dr Estavillo. “Because the basis of the mutation is a missing gene, it could be possible to create drought tolerance in commercially important crops by a traditional process of interbreeding instead of the transfer of foreign genes, alleviating public concerns about genetically-modified food.”