Lab+Life Scientist Oct 2014

Page 42

GM crops

replicate it in commercial cultivars of crop species,”

were developed to join things, or separate them - the

Hellens said.

same is true of most of the power tools in a modern garage,” Hellens said. ©

Hellens’ own research in recent times has focused on the biosynthesis pathways in fruit that produce flavonoid compounds and vitamin C, both potent antioxidants with potential health benefits for humans. But his team’s work to increase vitamin C concentrations in fruit has a broader goal: dietary vitamin C is crucial to the body’s ability to absorb

the emerging tools of molecular genetics are very good at making precise cuts, and excising DNA sequences with precision. “But we’re not particularly good at sticking things back together again. It’s particularly true for

iron. “Increasing vitamin C in plants doesn’t affect the concentration of iron in the plant, but it does enhance

involved, we have the tantalising prospect of elevating

the body’s ability to absorb iron,” Hellens said.

vitamin C concentrations in other plants in the human

“Around 1.6 billion people around the globe

“Most of the things we do involve breaking or cutting DNA, and sticking it together again. Some of

diet,” Hellens said.

plant DNA. “I believe that, in the future, we will develop a better understanding of the mechanisms involved in

are chronically anaemic because they don’t absorb

“We could prevent anaemia and keep people

enough iron from their diet. Elevating vitamin C

alive and healthy by editing the genomes of important

“When conventional plant breeders introduce

concentrations in the diet could help correct iron-

commodity crops to replicate naturally occurring alleles

a gene into a crop, and back-cross, they are doing

deficiency anaemia.”

in high-vitamin C species like kiwifruit, Kakadu plum,

basically the same thing - double-strand breaks are

Amazonian fruits like acerola and camu camu, or the

required for the recombination events that lead

Indian gooseberry,” Hellens said.

to the hybrid progeny, so you’re further blurring

Hellens says his team’s research has determined not only how vitamin C is made in fruit, but how its production is regulated.

Targeted methylation or demethylation of genes, and

homologous recombination.

the differences between molecular genetics and

Hellens says his team’s studies of kiwifruit, which

homologous recombination, are among future tools for

has 50 times the vitamin C of oranges, and Australia’s

manipulating the activity of genes in situ in crop plants.

Hellens says that for virtually every trait of

Kakadu plum, Terminalia ferdinandiana, which has the

Hellens says it is already possible to demethylate

importance in crop plants, there will be a pool of

highest concentration of vitamin C of any fruit in the

genes, but selectively silencing genes by target

genetic diversity within the crop and its wild relatives

world - 200 times more than oranges - have revealed

methylation is not yet feasible - however, it may be

to improve it. Rather than install the allele of interest,

that a single nucleotide substitution in the regulatory

possible, by demethylating repressor genes, to activate

the preferred approach will be to use homologous

region of an enzyme involved in vitamin C biosynthesis

dormant downstream genes, to achieve gain-of-

recombination to ‘overwrite’ the gene in situ in

changes one peptide in the enzyme, resulting in a very

function traits, Hellens said.

the crop plant - the trait might affect yield, disease

large increase in vitamin C concentration.

conventional breeding.”

Modifying genes in situ by homologous

resistance, drought tolerance, dwarfing - “We know

Vitamin C from fruits is more readily absorbed by

recombination has been used for years to create

that lots of alleles exist in the wild, and we can use

the human gut than vitamin C in the form of ascorbic

transgenic animals, but researchers have yet to find a

them,” he said.

acid tablets, sold by chemists.

way of making it work reliably in plants.

“Many traits are multigenic, but I don’t believe

“Although we’re only at the preliminary stages of

“I once drew an analogy between modern

the project, because we now understand the mechanism

molecular genetics and toolmaking: all primitive tools

42 | LAB+LIFE SCIENTIST - October 2014

any trait is so complex that it is not amenable to molecular dissection. |