A team of UK researchers has figured out how low-quality starch grows in wheat.
The discovery, published in The Plant Cell, could help to breed plants with more control over their starch.
As well as being an important nutritional source of carbohydrates, starch is a valuable ingredient in brewing, glue, paper, textiles, and construction materials.
In the plant tribe Triticeae, which includes wheat, barley, and rye, starch grows in two distinct granules: large “A-type” granules, and small, more problematic, “B-type” granules.
A-type granules are often better for making starchy things. B-type granules can get lost during flour milling because of their size, leading to waste. They also present problems when using starch for other things: too many B-type granules in beer, for instance, makes it cloudy.
These researchers have found the culprit that makes the B-type granules: an enzyme, or type of protein, called PHS1.
“We discovered that the ubiquitous enzyme, (PHS1) is crucial for the formation of B-type granules in wheat,” says lead author Dr Nitin Uttam Kamble, a postdoctoral scientist at the John Innes Centre, UK.
“This is a scientific breakthrough because decades of research on this enzyme have failed to find a clear role for PHS1 in plants, and it shows that the A- and B-type granules of wheat form via different biochemical mechanisms.
“We can now use this knowledge to create variations in starch for different food and industrial applications.”
The researchers found that the enzyme interacts with other B-type granule proteins in lab-based experiments.
They then bred wheat plants with mutated genomes that didn’t include a gene for PHS1, finding they had fewer B-type granules than the wild-type plants.
“Industry does not generally like heterogeneity; it wants something nice and even to process smoothly and having these different types of starch granules in wheat has always represented a challenge,” says group leader Dr David Seung, also at John Innes.
“So, for us to discover the enzyme responsible for making the smaller granule population and to be able to use our breeding platform to reduce the number of B-type granules will hopefully be of great interest to many industry users.
“Combined together with our previous work, we now have a panel of diverse, novel wheat starches that vary in granule morphology, and these have diverse physical and chemical properties.”
The researchers are now interested in seeing how these granules interact with digestibility, human health and cooking quality.
