RT Journal Article SR Electronic T1 Expression of E. coli glycogen branching enzyme in an Arabidopsis mutant devoid of endogenous starch branching enzymes induces the synthesis of starch-like polyglucans JF bioRxiv FD Cold Spring Harbor Laboratory SP 019976 DO 10.1101/019976 A1 Laura Boyer A1 Xavier Roussel A1 Adeline Courseaux A1 Ofilia Mvundza Ndjindji A1 Christine Lancelon-Pin A1 Jean-Luc Putaux A1 Ian Tetlow A1 Michael Emes A1 Bruno Pontoire A1 Christophe D’Hulst A1 Fabrice Wattebled YR 2015 UL http://biorxiv.org/content/early/2015/10/29/019976.abstract AB 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 origin 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.