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Front. Plant Sci. | doi: 10.3389/fpls.2018.00192

Novel bioengineered cassava expressing an archaeal starch degradation system and a bacterial ADP-glucose phosphorylase for starch self-digestibility and yield increase

  • 1Agriculture and Natural Resources, Delaware State University, United States
  • 2Department of Biochemistry and Molecular Biology, University of Georgia, United States
  • 3Department of Microbiology and Molecular Genetics and Department of Biochemistry and Molecular Genetics, Michigan State University, United States

To address national and global low-carbon fuel targets, there is great interest in alternative plant species such as cassava (Manihot esculenta), which are high-yielding, resilient, and are easily converted to fuels using the existing technology. In this study the genes encoding hyperthermophilic archaeal starch-hydrolyzing enzymes, -amylase and amylopullulanase from Pyrococcus furiosus and glucoamylase from Sulfolobus solfataricus, together with the gene encoding a modified ADP-glucose pyrophosphorylase (glgC) from Escherichia coli, were simultaneously expressed in cassava roots to enhance starch accumulation and its subsequent hydrolysis to sugar. A total of 13 multigene expressing transgenic lines were generated and characterized phenotypically and genotypically. Gene expression analysis using quantitative RT-PCR showed that the microbial genes are expressed in the transgenic roots. Multigene-expressing transgenic lines produced up to 60% more storage root yield than the non-transgenic control, likely due to glgC expression. Total protein extracted from the transgenic roots showed up to 10-fold higher starch-degrading activity in vitro than the protein extracted from the non-transgenic control. Interestingly, transgenic tubers released three-fold more glucose than the non-transgenic control when incubated at 85oC for 21-h without exogenous application of thermostable enzymes, suggesting that the archaeal enzymes produced in planta maintain their activity and thermostability.

Keywords: cassava, hyperthermophilic archaeal, glgC, starch self-processing, bioethanol, multigene-expression, starch-hydrolyzing enzymes

Received: 29 Aug 2017; Accepted: 01 Feb 2018.

Edited by:

Zeng-Yu Wang, Noble Research Institute, LLC, United States

Reviewed by:

Alberto A. Iglesias, National University of the Littoral, Argentina
Peng Zhang, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences (CAS), China  

Copyright: © 2018 Ligaba-Osena, Jones, Donkor, Chandrayan, Pole, Wu, Vieille, Adams and Hankoua. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Bertrand B. Hankoua, Delaware State University, Agriculture and Natural Resources, 1200 North Dupont Highway, Dover, 19901, DE, United States, bhankoua@desu.edu