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Glutathione transferases catalyze recycling of auto‐toxic cyanogenic glucosides in sorghum
Author(s) -
Bjarnholt Nanna,
Neilson Elizabeth H. J.,
Crocoll Christoph,
Jørgensen Kirsten,
Motawia Mohammed Saddik,
Olsen Carl Erik,
Dixon David P.,
Edwards Robert,
Møller Birger Lindberg
Publication year - 2018
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13923
Subject(s) - glutathione , hydrogen cyanide , nitrilase , chemistry , biochemistry , metabolism , cyanide , metabolite , enzyme , biology , stereochemistry , organic chemistry
Summary Cyanogenic glucosides are nitrogen‐containing specialized metabolites that provide chemical defense against herbivores and pathogens via the release of toxic hydrogen cyanide. It has been suggested that cyanogenic glucosides are also a store of nitrogen that can be remobilized for general metabolism via a previously unknown pathway. Here we reveal a recycling pathway for the cyanogenic glucoside dhurrin in sorghum ( Sorghum bicolor ) that avoids hydrogen cyanide formation. As demonstrated in vitro , the pathway proceeds via spontaneous formation of a dhurrin‐derived glutathione conjugate, which undergoes reductive cleavage by glutathione transferases of the plant‐specific lambda class ( GSTL s) to produce p ‐hydroxyphenyl acetonitrile. This is further metabolized to p ‐hydroxyphenylacetic acid and free ammonia by nitrilases, and then glucosylated to form p ‐glucosyloxyphenylacetic acid. Two of the four GSTL s in sorghum exhibited high stereospecific catalytic activity towards the glutathione conjugate, and form a subclade in a phylogenetic tree of GSTL s in higher plants. The expression of the corresponding two GSTL s co‐localized with expression of the genes encoding the p ‐hydroxyphenyl acetonitrile‐metabolizing nitrilases at the cellular level. The elucidation of this pathway places GST s as key players in a remarkable scheme for metabolic plasticity allowing plants to reverse the resource flow between general and specialized metabolism in actively growing tissue.