TY - JOUR T1 - <em>E. coli</em> glycogen branching enzyme restores synthesis of starch-like polyglucans in an <em>Arabidopsis</em> mutant devoid of endogenous starch branching enzymes JF - bioRxiv DO - 10.1101/019976 SP - 019976 AU - Laura Boyer AU - Xavier Roussel AU - Adeline Courseaux AU - Ofilia Mvundza Ndjindji AU - Christine Lancelon-Pin AU - Jean-Luc Putaux AU - Ian Tetlow AU - Michael Emes AU - Bruno Pontoire AU - Christophe D’Hulst AU - Fabrice Wattebled Y1 - 2015/01/01 UR - http://biorxiv.org/content/early/2015/05/29/019976.abstract N2 - Starch synthesis requires several enzymatic activities including branching enzymes (BEs) responsible for the formation of α(1→6) linkages. Distribution and number of these linkages are further controlled by debranching enzymes (DBEs) that cleave some of them, rendering the polyglucan water-insoluble and semi-crystalline. Although the activity of BEs and DBEs is mandatory to sustain normal starch synthesis, the relative importance of each in the establishment of the plant storage polyglucan (i.e. water-insolubility, crystallinity, presence of amylose) is still debated. Here, we have substituted the activity of BEs in Arabidopsis with that of the Escherichia coli glycogen branching enzyme (GlgB). The latter is the BE counterpart in the metabolism of glycogen, a highly branched water-soluble and amorphous storage polyglucan. GlgB was expressed in the be2 be3 double mutant of Arabidopsis that is devoid of BE activity and consequently free of starch. The synthesis of a water-insoluble, partly crystalline, amylose-containing starch-like polyglucan was restored in GlgB-expressing plants, suggesting that BEs only have a limited impact on establishing essential characteristics of starch. Moreover, the balance between branching and debranching is crucial for the synthesis of starch, as an excess of branching activity results in the formation of highly branched, water-soluble, poorly crystalline polyglucan. ER -