Introduction of glucan synthase into the cytosol in wheat endosperm causes massive maltose accumulation and represses starch synthesis
David, Laure C.
The Plant Journal
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Schreier, T. B., Fahy, B., David, L. C., Siddiqui, H., Castells‐Graells, R., & Smith, A. M. (2021). Introduction of glucan synthase into the cytosol in wheat endosperm causes massive maltose accumulation and represses starch synthesis. The Plant Journal https://doi.org/10.1111/tpj.15246
SUMMARY: We expressed a bacterial glucan synthase (Agrobacterium GlgA) in the cytosol of developing endosperm cells in wheat grains, to discover whether it could generate a glucan from cytosolic ADP‐glucose. Transgenic lines had high glucan synthase activity during grain filling, but did not accumulate glucan. Instead, grains accumulated very high concentrations of maltose. They had large volumes during development due to high water content, and very shrivelled grains at maturity. Starch synthesis was severely reduced. We propose that cytosolic glucan synthesized by the glucan synthase was immediately hydrolysed to maltose by cytosolic β‐amylase(s). Maltose accumulation resulted in a high osmotic potential in developing grain, drawing in excess water that stretched the seed coat and pericarp. Loss of water during grain maturation then led to shrinkage when the grains matured. Maltose accumulation is likely to account for the reduced starch synthesis in transgenic grains, through signalling and toxic effects. Using bioinformatics, we identify an isoform of β‐amylase likely to be responsible for maltose accumulation. Removal of this isoform through identification of TILLING mutants or genome editing, combined with co‐expression of heterologous glucan synthase and a glucan branching enzyme, may in future enable elevated yields of carbohydrate through simultaneous accumulation of starch and cytosolic glucan.
Original Article, Original Articles, wheat grain, bacterial glucan synthase, endosperm development, maltose, starch, Triticum aestivum
Biotechnology and Biological Sciences Research Council (BB/J004596/1, BB/J004561/1, BB/K006517/1, BB/P016855/1)
External DOI: https://doi.org/10.1111/tpj.15246
This record's URL: https://www.repository.cam.ac.uk/handle/1810/321951