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Friday, July 29, 2011

Programmed cell death in plants revealed


Arabidopsis plant used for genetic research
Image: dra_schwartz/iStockphoto
Research at La Trobe University has provided new insight into how programmed cell death may be controlled in plants.
The work, led by plant biologist Professor Roger Parish, is reported in the latest issue of the international scientific journal, The Plant Cell, published by the American Society of Plant Biologists.

As the world’s population rises and demand for food and bio-fuel increases, it has important implications for improving agricultural crop production.
Key to the La Trobe study is the discovery of an enzyme, aspartic protease, called ‘UNDEAD’

With its Zombie connotation, the enzyme helps decide such things as when cells in the tapetal layer – which provides building blocks for the pollen – live or die.

‘One of the big issues in plants, just as in animals and humans, is programmed cell death,’ explains Professor Parish. ‘To date nobody has really known how it works in plants. There have been lots of theories.

‘It’s very important for plant development that certain cells die at the right time so that the plant can develop and reproduce – so this new work is a real breakthrough,’ he says. Other members of the La Trobe research team are Dr Huy Anh Phan, Dr Sylvana Iacuone, and Dr Song F Li.

The new discovery follows previous studies by Professor Parish’s research group on male sterility and anther development in plants. This has already led to new technology for hybrid seed production. The researchers are also working on ways to help protect plants against cold and dehydration.

A few years ago the La Trobe group discovered a ‘Godfather’ gene (AtMYB80) which acts as a master ‘switch’ for pollen production.  When researchers ‘knocked out’ this gene, plants became male sterile. When they reversed the process, re-inserting the gene with some modification, plants again began to produce pollen.

It is this system that is now used to produce seeds with ‘hybrid vigour’, a trait which leads to increased yields.

Key to producing hybrid seeds is the ability to stop plants from self pollinating. This system can also be used to contain genetically engineered plants, and stop seeds from setting so plants can direct extra energy into making more leaves.

The latest La Trobe research also provides insights into the role of a host of other biochemical players involved in the process of cell death that is triggered by the master gene.

The researchers identified more than 400 genes controlled by the master gene. They isolated and identified various suspects and tracked down one that ‘codes’ for an aspartic protease enzyme called UNDEAD that digests, or breaks down, other proteins.

‘This gene, along with AtMYB80, appears to regulate the timing of programmed cell death in the tapetum,’ says Professor Parish.

The La Trobe research was carried out on Arabidopsis thaliana, or thale cress. The same genes are found in wheat, barley, canola, cotton, broccoli, rice, cabbage – and even poplar trees. So the work can be applied to improve plants for a wide range of agricultural industries.

Professor Parish’s lab also specialises in the mechanisms of seed mucilage production and seed coat development. It is funded by the Grains Research and Development Council, the Australian Research Council and the company Pacific Seeds.

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