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Mannan-related enzymes of wheat endosperm

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Mannan structure in wheat grain no longer an enigma

Mannan is a key molecular player in wheat grain development and food storage. A first, EU researchers have characterised the structure of wheat mannan and the genes behind its formation using new genetic methods.

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The EU-funded project MANAN, with a Marie Skłodowska-Curie Individual Fellowships scheme grant, has provided a knowledge platform to help equip future research into mannan. Potential uses include products for the rapidly expanding areas of food industry, agriscience and biomed. Challenging previous structure models MANAN project coordinator Dr Luc Saulnier of the French National Institute for Agricultural Research, INRA outlines: “We had three goals, to elucidate mannan’s structure, its biosynthesis and its role in grain development.” The MANAN team isolated and characterised the structure of wheat grain mannan, challenging previous models in existing literature. Not just a first for the team, the exact structure is important to all related research, especially for future genetics and biochemistry applications. The researchers also showed that mannan is present in the endosperm, responsible for nourishing the developing embryo, and appears early in grain development. The genes behind the molecule As mannan is ubiquitous throughout the plant world, the MANAN team extended its research to other plants in search of the genes involved in its biosynthesis. The cellulose synthase-like (CSL) family of genes, including the sub-group CSLA, are present in modern-day plants as well as ancestors such as primitive algae. Project researchers studied the role of CSLA genes in mannan synthesis using several sources: mutants of wheat in collaboration with Rothamsted Research Centre in the United Kingdom, yeast (Pichia) in collaboration with Heinrich Heine University in Germany and Arabidopsis in collaboration with Berkeley University in the United States. “In yeast we successfully produced wheat-like mannan showing that the candidate CSLA gene encodes the enzyme responsible for the synthesis of the mannan backbone,” says Dr Saulnier. Work is still in progress in Arabidopsis and the team are finishing the characterisation of Arabidopsis mutants, the next step before publication of the results. A flexible future for mannan Mannan can form galactomannan or glucomannan, used as thickeners in various domains including food and the mining industry. However, mannans in wheat have clearly totally different structures and functions. To underline the importance of mannan in plants, studies on Arabidopsis plants lacking mannan or glucomannan in seeds are either barely viable or embryo lethal. “When its role is fully elucidated, it’s likely that mannan could potentially impact grain shape or size and therefore cereal yields,” says Dr Saulnier. Challenges and lessons for future research Based on project findings, and recent literature data, mannan is seen as a fundamental structure, essential for early cell development and whole plant development. “Our main issues concerned the wheat mutants’ approach that didn’t work as expected due to the complexity of the wheat genome. Therefore, we used other systems (Arabidopsis and yeast) to demonstrate the role of the CSLA candidate genes,” explains Dr Saulnier. “Unfortunately, using these systems does not allow us to decipher the physiological and technological impact of mannan in wheat grain,” he points out. This research is of potential interest to various industrial sectors – plant breeding, milling and biofuel industries active in Europe – and represents a good opportunity to improve competitiveness of European agriculture. “As such, further research along this path promises to yield useful data,” Dr Saulnier concludes.

Keywords

MANAN, mannan, wheat, gene, grain, CSLA, biosynthesis, embryo

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