Understanding cell death in plants

Posted on September 5, 2011

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Researchers tracks down genetic ‘hit squad’ to improve agricultural production:

Understanding cell death in plants

It sounds a bit like Underbelly, but you won’t find it on television…

This particular drama unfolded in the lab of La Trobe University plant biologist Professor Roger Parish, and is featured in a recent issue of the international scientific journal, The Plant Cell, published by the American Society of Plant Biologists.

It’s a tale of grand scientific detective work, a Godfather-like genetic ‘master switch’, biochemical ‘hit-squads’ of ‘killer’ proteins that cause premature cell death, and an enzyme, aspartic protease, called ‘UNDEAD’, that helps decide when cells in the tapetum – where plants manufacture their valuable gold pollen – live or die.

The tapetum, explains Professor Parish, is a layer of cells in the pollen sac that have to be sacrificed at the correct stage of plant development so that plants can make pollen. Otherwise the plants become male sterile.

The work of his research group, part of long-term studies on male sterility and anther development in plants, has already resulted in new technology for hybrid seed production for agriculture. 
It achieved this a few years ago when it discovered a ‘Godfather’ gene (called AtMYB80) which acts as a master ‘switch’. 

When researchers ‘knocked out’ this gene, cells in the tapetum died and the plant became sterile. When the process was reversed and the gene re-inserted with some modification, the opposite happened and plants again began to produce pollen.

Stops self pollination

This system is now being used to produce seeds with ‘hybrid vigour’ because it stops plants from self pollinating. It can also ensure the containment of genetically engineered plants, and stop seeds from setting so plants can put extra energy into making more leaves.

The La Trobe research team has now published the next step, having come to grips with the host of other biochemical players involved down the chain in the process of cell death that is triggered by this master gene.

‘One of the big issues in plants, just as in animals, is programmed cell death,’ explains Professor Parish. ‘But nobody really knows how it works in plants. There are lots of theories.

‘It’s very important for plant development that certain cells die at the right time so that the plant can do what it has to do – so this new work is a real breakthrough,’ he says.

First-time insights

Flowering thale cress

The work was carried out by molecular and cell biologists Dr Huy Anh Phan, Dr Sylvana Iacuone, Dr Song F. Li and Professor Parish. They have provided for the first time insight into how such programmed cell death is regulated in plants.

The researchers identified more than 400 other genes controlled by this master gene. They isolated and identified the 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.

‘So as long as our master gene is turned on,’ says Professor Parish, ‘the protease is produced and when the master gene is turned off, the protease gene is also turned off.  Then programmed cell death starts because if we block the gene coding for the protease we get premature cell death, in exactly the same way as when we knock out the master switch.

Counter-intuitive

‘What that means, and it’s kind of counter-intuitive, you have a protease that protects the cells from death, probably by digesting ‘killer proteins’. Intriguingly, UNDEAD is targeted to the mitochondrion and mitochondria are known to play a critical role in animal programmed cell death.

‘So for the first time we have an insight into how programmed cell death may be controlled in plants,’ says Professor Parish.

The La Trobe research was carried out on Arabidopsis thaliana, or thale cress, but Professor Parish says 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.

Having identified anther-specific genes essential for pollen production and now shed new light on their regulatory pathways, the researchers are also working on genes that can help protect plants against cold and dehydration.

His 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

The scientific paper can be found here.