Research holds out hope for safer crop pest control

Research holds out hope for safer crop pest control

15 Jan 2008

Research into a series of circular proteins – first found in plants used by African women to help accelerate childbirth – may lead to a new class of natural, more ecologically friendly insecticides.

This possibility is highlighted by a La Trobe University study carried out in association with the University of Queensland, and just published in the prestigious US journal, Proceedings of the National Academy of Sciences.

The proteins, cyclotides (a group of very stable cyclic mini-peptides), have also attracted attention for their pharmaceutical applications, as a possible platform for new ways of drug delivery for human diseases.

The new research involved detailed biochemical and microscopy studies. It reveals how plant cyclotides disrupt epithelial cells in the midgut of lepidopteran larvae. Lepidoptera are insects such as butterflies, moths and skippers which, during their larval phase, can cause substantial crop losses.

The work was carried out by La Trobe biochemists Ms Barbara Barbeta, PhD student Amanda Gillon and Professor Marilyn Anderson in association with zoologist Dr Alan Marshall from the University’s Analytical Microscopy Laboratory, and Professor David Craik from the Institute for Molecular Bioscience, University of Queensland.

The project examined both the way in which larvae react to different amounts of the cyclotides in their diet as well as the importance of the circular structure of the protein.

Professor Marilyn Anderson heads the La Trobe University biochemistry laboratory at which much of the research was carried out. She says cyclotides are found at high levels in the leaves, stems, and roots of several plant species such as Rubiaceae and Violaceae.

The cyclotides used in this study were first isolated from the plant Oldenlandia affinis in Africa in the 1970s by a Norwegian Red Cross worker, Dr Lorentz Gran. However, it was not until 1995 that the circular nature and structure of one of the cyclotides, known as ‘kalata B1’, was solved by Professor Craik.

Professor Anderson says the project began six years ago when a La Trobe PhD student fed the kalata B1 cyclotide to a lepidopteran larva and noticed that it stopped growing. Subsequent studies found that cells in the larval gut, responsible for absorbing nutrients, were either damaged or destroyed.

More work indicated that higher concentrations of cyclotides destroyed these gut cells, while lower levels led to the shedding of the cells, a process that could be reversed when the protein was withdrawn from the larvae diet because the cells regenerated.

The new study shows that while control larvae doubled in size, larvae on high-concentration kalata B1 diet did not grow and consumed very little food.

‘Ingestion of cyclotides caused marked changes in the midgut of lepidopteran pests and provides an explanation for the observed insecticidal activity of cyclotides,’ Professor Anderson says.

‘At the highest concentration of cyclotide very little diet was consumed but the larvae did not die, which suggests the cyclotide is not highly toxic – and that the failure to grow was probably caused by the lack of nutrient intake.’

Turning to their work on the molecular structure of the cyclotides, the researchers say: ‘Because a break in the peptide backbone was sufficient to neutralize kalata B1 activity in this study, we suggest that the circular backbone is important in maintaining framework stability, which, in turn, is essential for insecticidal activity.’

Further details

For interviews and further information, please contact Professor Marilyn Anderson on tel: +613 9479 1255; email: m.anderson@latrobe.edu.au; website: https://www.latrobe.edu.au/biochemistry/lab/anderson/

A full report of the research can be found on the following website: http://www.pnas.org/

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