Production of very-high-amylose cassava by post-transcriptional silencing of branching enzyme genes.

Wenzhi Zhou,Jun Yang,Xiaomeng Hao,Shanshan Zhao,Peng Zhang,Qiuxiang Ma,Xinlu Lu,Shutao He,Hongxia Wang

doi:10.1111/jipb.12848

Wenzhi Zhou, Jun Yang + Show 7 more

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https://doi.org/10.1111/jipb.12848

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Abstract

High amylose starch can be produced by plants deficient in the function of branching enzymes (BEs). Here we report the production of transgenic cassava (Manihot esculenta Crantz) with starches containing up to 50% amylose due to the constitutive expression of hair-pin dsRNAs targeting the BE1 or BE2 genes. All BE1-RNAi plant lines (BE1i) and BE2-RNAi plant lines (BE2i) were grown up in the field, but with reduced total biomass production. Considerably high amylose content in the storage roots of BE2i plant lines was achieved. Storage starch granules of BE1i and BE2i plants had similar morphology as wild type (WT), however, the size of BE1i starch granules were bigger than that of WT. Comparisons of amylograms and thermograms of all three sources of storage starches revealed dramatic changes to the pasting properties and a higher melting temperature for BE2i starches. Glucan chain length distribution analysis showed a slight increase in chains of DP>36 in BE1i lines and a dramatic increase in glucan chains between DP 10-20 and DP>40 in BE2i lines. Furthermore, BE2i starches displayed a B-type X-ray diffraction pattern instead of the A-type pattern found in BE1i and WT starches. Therefore, cassava BE1 and BE2 function differently in storage root starch biosynthesis.

Highlights

Cassava (Manihot esculenta Crantz) is one of the most important starchy crops worldwide, providing staple food for more than 700 million people in the tropics and subtropics (Hershey, 2017)
The heights ranged from 1.7 m (BE1i-13) to 2.1 m (BE1i-18) for BE1-RNAi plant lines (BE1i) lines, and 1.4 m (BE2i-24) to 2.0 m (BE2i-58) for BE2-RNAi plant lines (BE2i) lines (Fig1 a, b), both of which were shorter than wild type (WT)
The biomass per plant ranged from 0.7 kg (BE1i-13) to 1.6 kg (BE1i-26) for BE1i lines and 0.9 kg (BE2i-24) to 1.4 kg (BE2i-38, BE2i-59) for BE2i lines (Fig1 a, c), which is much lighter than the average fresh weight of WT (3.5 kg)

Summary

Introduction

Cassava (Manihot esculenta Crantz) is one of the most important starchy crops worldwide, providing staple food for more than 700 million people in the tropics and subtropics (Hershey, 2017). Unlike the traditional physical and/or chemical starch modifications, breeders intend to produce new cassava varieties with modified starches to expand their application spectrum through genetic approaches, such as starch-related mutant identification and reverse-genetic/biotechnological approaches (Schwall et al, 2000; Jobling et al, 2002; Raemakers et al, 2005; Ceballos et al, 2007; Zhao et al, 2011; Bull et al, 2018). The SSS, BE, and DBE are involved in amylopectin synthesis, and GBSS is the key enzyme for amylose biosynthesis in plants including cassava (Zhao et al, 2011; Bull et al, 2018)

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