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ScienceWise - Autumn 2010

Can DNA Packaging in Plants Affect our Diet?

Article Illustration
Professor Barry Pogson, Dr Christopher Cazzonelli with students Andrea Roberts and Alice Burgess in the Plant Growth Room

Regulating Pigment Composition and Plant Architecture

Carotenoids are the second most abundant  class of coloured organic pigments on Earth. They tend to absorb blue light giving them a characteristic red, orange or yellow colour. Carotenoids serve a central role in the chemistry of photosynthesis and are found in many plants, algae, fungi and bacteria. They are what give many fruits their distinctive coulors and are also responsible for the vibrant hues of autumn leaves.

Beyond their role in plants, Carotenoids are also vital to the biochemistry of most animals, including humans. However, unlike plants, animals do not directly produce carotenoids, so they have to get those they need from their diet. Lack of β-carotene, a vitamin A precursor, can lead to deterioration of the immune system and blindness. Consequently, fruit and vegetables are an essential dietary requirement for humans. But not all food colours are due to carotenoids, so not all plants provide an adequate source.

Dr Christopher Cazzonelli is a Research Associate at the Research School of Biology, ANU. He is a member of the Pogson lab in the ARC Centre of Excellence in Plant Energy Biology - a cutting edge research centre focused on better understanding the way in which plants produce and use their energy systems in response to environmental change. 

Professor Pogson gave Dr Cazzonelli the challenge of finding what limits the production of carotenoids in plants and it wasn’t long before he had identified a chromatin-modifying gene, SET DOMAIN GROUP 8 (SDG8). He found that it regulates carotenoid composition as well as flowering time, seed set, germination, root development and shoot branching.

Dr Cazzonelli says, “Loss of function of SDG8 limits production of a carotenoid called lutein, (the same compound that prevents age-related macular degeneration of the human eye.) Furthermore, we have found preliminary evidence of novel hormonal-like roles for carotenoids in the differentiation of plant stem cells into roots, leaves and flowers.”

Such modifications in cell structure that arise from external factors rather than directly from the cell’s DNA are known as epigenetic changes and are becoming an increasingly important area of research.

In response to environmental pressures, organisms have evolved to reversibly modify DNA-binding proteins. These proteins regulate how DNA is packaged within the nucleus of the cell. This affects gene expression and cell function without changing the original DNA sequence, creating a ‘memory process’.

Unlike genetic modifications, which lead to the inheritance of genetic information, such epigenetic modifications can mediate the transmission of an active or silent state of gene expression without altering the primary DNA sequence. As these modifications can be reversible, they can form the basis of a controllable regulatory mechanism.

The essential roles of carotenoids, as well as the chromatin-modifying nature of SDG8, have opened a new door towards understanding regulatory mechanisms that control plant development. The team are now investigating when and why epigenetics regulates carotenoids in fruits and cereals and how this effects plant development.

This further research has many possible applications and could one day help developing countries by preventing the medical problems associated with gross Vitamin A deficiency.

Dr Cazzonelli found inspiration and a mentor whilst growing up on the Tablelands in Far North Queensland. In between racing dirt bikes around his parents’ crayfish farm, his neighbour would excite him with stories about molecular biology and its potential. He says, “Our discussions were complex: proteins, DNA, chromosomes, things that we didn’t know a lot about in the late eighties and because it was so hard, I figured that if I could study it and be good at it, that I would have an edge, an advantage out there in the job market, so I took that chance and it has paid off.“

He now has many peer-reviewed data papers including a publication in Plant Cell, the plant biology research journal with the highest number of citings. However, he plays down his blossoming scientific career by saying, “I enjoy working as a Plant Molecular Biologist, while I am not racing motocross!”

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