By Alison Ballance
Petunias are a popular garden plant, and plant breeders have put a lot of effort into breeding 'mutant petunias' that boast spectacular colours and patterns. Such mutant plants interest Nick Albert, not as a gardener, but as a geneticist who is trying to unlock the genetic codes that underpin how pigmentation and colour patterns are expressed. Nick is quick to point out that the term mutant is a straight-forward genetic term that describes any variant of a plant that has been bred from an ancestral type.
Nick is interested in pigments known as anthocyanins, which are responsible for the reds, blues and purples in plant colour. They belong to a class of molecules called flavonoids. Yellows and oranges, on the other hand, are produced by carotenoid pigments, while chlorophylls produce greens.
Nick's interest in anythocyanins began during his PhD research at Massey University.
"We’re doing a lot of work understanding how the 15 genes that produce pigments]are turned on at the right time and place," says Nick. "And they’re regulated by a set of very special genes – these genes are the regulatory genes. And these proteins have partners, and they can only turn on their genes when their partner is present."
"A lot of previous work had been done on how genes are turned on. But I was really interested in the mechanisms that might allow the plant to turn off colour, or to put the brakes on so that excessive amounts of pigment aren’t produced at the wrong time. We’ve identified two different classes of genes that turn off these genes."
The two genes Nick has identified work in quite different ways. One essentially hijacks the activating part of those proteins and instead of allowing that complex to turn on the genes it turns the switch off – and it’s like the handbrake, it’s a very effective way of turning genes off. Then there’s another type of repression and this a small, interfering mechanism, more like damping on the pedal brake.
Nick says pigments are an important way for plants to respond to stress. “If conditions become unfavourable plants can’t move – and these systems allow the plant to respond very rapidly to changing conditions.”
David Lewis from Plant and Food Research says that understanding the genetic regulation of pigment production in petunias may be useful in breeding coloured fruits and vegetables, as pigments have recognised health benefits.
During a post-doctoral position at AgResearch Nick, who now works at Plant and Food Research, looked at how tannins, which are another group of flavonoids, were regulated in clover. Plants use tannins to deter insects from feeding on them. Tannin production in forage crops is important as it improves nitrogen use efficiency in the rumen of animals such as cows, and can help prevent bloat.
Nick was awarded the 2014 Roger Slack Award in Plant Biology by the New Zealand Society of Plant Biologists.