Metabolic consequences of knocking out UGT85B1, the gene encoding the glucosyltransferase required for synthesis of dhurrin in Sorghum bicolor (L. Moench).
Many important food crops produce cyanogenic glucosides as natural defense compounds to protect against herbivory or pathogen attack. It has also been suggested that these nitrogen-based secondary metabolites act as storage reserves of nitrogen. In sorghum, three key genes, CYP79A1, CYP71E1 and UGT85B1, encode two Cytochrome P450s and a glycosyltransferase, respectively, the enzymes essential for synthesis of the cyanogenic glucoside dhurrin. Here, we report the use of targeted induced local lesions in genomes (TILLING) to identify a line with a mutation resulting in a premature stop codon in the N-terminal region of UGT85B1. Plants homozygous for this mutation do not produce dhurrin and are designated tcd2 (totally cyanide deficient 2) mutants. They have reduced vigor, being dwarfed, with poor root development and low fertility. Analysis using liquid chromatography-mass spectrometry (LC-MS) shows that tcd2 mutants accumulate numerous dhurrin pathway-derived metabolites, some of which are similar to those observed in transgenic Arabidopsis expressing the CYP79A1 and CYP71E1 genes. Our results demonstrate that UGT85B1 is essential for formation of dhurrin in sorghum with no co-expressed endogenous UDP-glucosyltransferases able to replace it. The tcd2 mutant suffers from self-intoxication because sorghum does not have a feedback mechanism to inhibit the initial steps of dhurrin biosynthesis when the glucosyltransferase activity required to complete the synthesis of dhurrin is lacking. The LC-MS analyses also revealed the presence of metabolites in the tcd2 mutant which have been suggested to be derived from dhurrin via endogenous pathways for nitrogen recovery, thus indicating which enzymes may be involved in such pathways.
School of Biological Sciences, Monash University, Wellington Rd, Clayton, 3800 Australia.
Cecilia K
CK
Blomstedt
School of Biological Sciences, Monash University, Wellington Rd, Clayton, 3800 Australia Present address: Plant Health Australia, level 1, 1 Phipps Close, Deakin, 2600 Australia.
Natalie H
NH
O'Donnell
Plant Biochemistry Laboratory and VILLUM research center for 'Plant Plasticity', Department of Plant and Environmental Sciences, University of Copenhagen, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark.
Nanna
N
Bjarnholt
School of Biological Sciences, Monash University, Wellington Rd, Clayton, 3800 Australia.
Alan D
AD
Neale
School of Biological Sciences, Monash University, Wellington Rd, Clayton, 3800 Australia Present address: Centre for Regional and Rural Futures (CeRRF), Deakin University, 75 Pigdons Rd, Waurn Ponds, 3216, Australia.
John D
JD
Hamill
Plant Biochemistry Laboratory and VILLUM research center for 'Plant Plasticity', Department of Plant and Environmental Sciences, University of Copenhagen, 40 Thorvaldsensvej, DK-1871 Frederiksberg C, Copenhagen, Denmark Carlsberg Laboratory, Gamle Carlsberg Vej 10, DK-1799 Copenhagen V, Denmark.
Birger Lindberg
BL
Møller
School of Biological Sciences, Monash University, Wellington Rd, Clayton, 3800 Australia ros.gleadow@monash.edu.
Roslyn M
RM
Gleadow
D002853:Chromatography, Liquid; D055786:Gene Knockout Techniques; D017343:Genes, Plant; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism; D006856:Hydrogen Cyanide / Q000378:metabolism; D013058:Mass Spectrometry; D055442:Metabolome; D055432:Metabolomics; D009154:Mutation / Q000235:genetics; D009566:Nitrates / Q000378:metabolism; D009570:Nitriles / Q000737:chemistry / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism; D010641:Phenotype; D030821:Plants, Genetically Modified; D045868:Sorghum / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*
D009566:Nitrates; D009570:Nitriles; D006856:Hydrogen Cyanide; D005964:Glucosyltransferases; D009584:Nitrogen; C011220:dhurrin
Cyanogenic glucoside; Detoxification; Dhurrin; Metabolic turnover; Sorghum; UDP-glycosyltransferase