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Dr Liz Dennis was interviewed in 2000 for the Australian Academy of Science's '100 Years of Australian Science' project funded by the National Council for the Centenary of Federation. This project is part of the Interviews with Australian scientists program. By viewing the interviews in this series, or reading the transcripts and extracts, your students can begin to appreciate Australia's contribution to the growth of scientific knowledge.
The following summary of Dennis's career sets the context for the extract chosen for these teachers notes. The extract highlights Dennis's interest in plant gene regulation and how plants respond to environmental stimuli. Use the focus questions that accompany the extract to promote discussion among your students.
Elizabeth Dennis was born in Sydney, New South Wales in 1943. She was educated at Methodist Ladies College, NSW. She attended the University of Sydney, gaining a BSc Hons in 1964 and a PhD in 1968.
Her postdoctoral work (1968-70) was with Dr Julius Marmur at the Albert Einstein College of Medicine in New York. In 1970 Dennis went to the University of Papua New Guinea, where she lectured in biochemistry and did DNA and chromosome studies on native rodents. During this time, she wrote a book with zoologist Jim Menzies on the rodents of Papua New Guinea.
From 1972-74 she worked at the CSIRO Division of Plant Industry in Canberra, returning to the University of Papua New Guinea as a senior lecturer in biochemistry (1974-76). Dennis moved back to Plant Industry in 1976 and is now chief research scientist.
Her research is in the general area of plant molecular biology. She has worked on Arabidopsis (an ideal plant to study because of its small genome size) and chaired the Multinational Arabidopsis Genome Project steering committee from 1993 to 1994.
Dennis became a Fellow of the Australian Academy of Technological Sciences and Engineering in 1987 and was awarded the Pharmacia LKB/Biotechnology Medal of the Australian Biochemistry Society in 1988. She became a Fellow of the Australian Academy of Science in 1995 and won the Avon 'Spirit of Achievement' award in 1997. In 2000, she and Dr Jim Peacock were awarded the inaugural Prime Minister's Prize for Science for their work on the flower switch gene, a key gene in determining when plants end their vegetative growth phase and begin flowering.
You also have an interest in the flowering of plants. In general terms, what is that about?
That is very much our current project, involving all the people in the lab. Flowering is an important developmental process in plants, a very exciting biological process. In animals you set aside your germ cells early in development, but in plants there is a growing point which starts by making leaves and stems and vegetative structures but then switches to making reproductive structures like flowers and pollen, all the components that make up flowers. So how does that switch occur? How do cells derived from the one growing point change from making vegetative to reproductive cells?
Using Arabidopsis, we isolated a mutant that didn’t flower till very late, and then we isolated the gene that was mutated to cease this effect. We could show that this gene acts as a repressor of flowering: the more of the gene product there is – the more the gene is switched on – the later the plant flowers. It’s a quantitative controller of flowering time. Later we found that this gene is down-regulated by vernalisation, a response to a period of cold which has long been known to cause plants to flower.
Plants need to flower in the springtime, not when there might be frosts or when they won’t have enough time to get their seeds mature for the next generation. They can’t go inside when it’s cold, so it is very important to them to flower at the right time and they’ve evolved mechanisms to ensure this happens. One of those mechanisms uses the cold as a signal. That is, many plants require a period of cold – a cold winter – in order to flower in the spring. They may also use day length (they recognise when the days get longer) as well as vernalisation to ensure that flowering occurs at the right time. We’ve found that the vernalisation, or cold, switches off the repressor gene called FLC – flowering LOCUS C. After this repressor of flowering is switched off by the period of cold, the plants flower. So we have a molecular basis for one of the long-standing question in plant biology – how does vernalisation work?
You’ve also been interested in the regulation of plant genes, haven’t you?
Yes. That’s the basic theme that makes it all hang together. The major project we’ve had, over a long time, is looking at genes being switched on by low oxygen, such as occurs in flooding or waterlogging. When plants are flooded they can’t run away. If it gets wet for you and me, we just walk away, but the plants are stuck. Plants have evolved mechanisms to cope with stresses caused by their being sedentary. So, when plants are flooded, they switch their metabolism from oxidative metabolism – oxidative phosphorylation – to fermentation. They make alcohol: the genes for the ethanol fermentation pathway are switched on. Instead of pyruvate going into the Krebs cycle, it enters the ethanol fermentation pathway where it is converted first to acetaldehyde and then to alcohol, using the enzmes pyruvate decarboxylase and alcohol dehydrogenase.
Over the years we have looked at these genes switched on by low oxygen, trying to identify the promoter motif so important for switching them on. In fact, all these genes have the same anaerobic response elements, so they all have a DNA sequence, upstream of the gene – a promoter element – that’s important in the glycolysis and low oxygen metabolism alcohol fermentation pathways. We’ve now identified the protein that binds to that low oxygen control element. That’s the sort of thing we’ve been interested in, with a view to trying to help Australian agriculture by making plants more resistant to waterlogging.
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