Cyanogen Metabolism in Cassava Roots: Impact on Protein Synthesis and Root Development

Journal Article · 24 February 2017 · Frontiers in Plant Science

DOI: https://doi.org/10.3389/fpls.2017.00220 · OSTI ID:1628280

Zidenga, Tawanda ^[1]; Siritunga, Dimuth ^[2]; Sayre, Richard T. ^[3]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Biosciences Division
2. Univ. of Puerto Rico, Mayaguez (Puerto Rico). Dept. of Biology
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States). Biosciences Division; New Mexico Consortium, Los Alamos, NM (United States)

Cassava (Manihot esculenta Crantz), a staple crop for millions of sub-Saharan Africans, contains high levels of cyanogenic glycosides which protect it against herbivory. However, cyanogens have also been proposed to play a role in nitrogen transport from leaves to roots. Consistent with this hypothesis, analyses of the distribution and activities of enzymes involved in cyanide metabolism provides evidence for cyanide assimilation, derived from linamarin, into amino acids in cassava roots. Both β-cyanoalanine synthase (CAS) and nitrilase (NIT), two enzymes involved in cyanide assimilation to produce asparagine, were observed to have higher activities in roots compared to leaves, consistent with their proposed role in reduced nitrogen assimilation. In addition, rhodanese activity was not detected in cassava roots, indicating that this competing means for cyanide metabolism was not a factor in cyanide detoxification. In contrast, leaves had sufficient rhodanese activity to compete with cyanide assimilation into amino acids. Using transgenic low cyanogen plants, it was shown that reducing root cyanogen levels is associated with elevated root nitrate reductase activity, presumably to compensate for the loss of reduced nitrogen from cyanogens. Finally, we overexpressed Arabidopsis CAS and NIT4 genes in cassava roots to study the feasibility of enhancing root cyanide assimilation into protein. Optimal overexpression of CAS and NIT4 resulted in up to a 50% increase in root total amino acids and a 9% increase in root protein accumulation. However, plant growth and morphology was altered in plants overexpressing these enzymes, demonstrating a complex interaction between cyanide metabolism and hormonal regulation of plant growth.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER). Biological Systems Science Division; Bill and Melinda Gates Foundation
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1628280
• Journal Information: Frontiers in Plant Science, Vol. 8; ISSN 1664-462X
• Publisher: Frontiers Research FoundationCopyright Statement
• Country of Publication: United States
• Language: English