Genetic dissection of cyclic pyranopterin monophosphate biosynthesis in plant mitochondria

Kruse, I., MacLean, A. E., Hill, L. and Balk, J. (2018) Genetic dissection of cyclic pyranopterin monophosphate biosynthesis in plant mitochondria. Biochemical Journal, 475(2), pp. 495-509. (doi: 10.1042/BCJ20170559) (PMID:29247140) (PMCID:PMC5791162)

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Mitochondria play a key role in the biosynthesis of two metal cofactors, iron–sulfur (FeS) clusters and molybdenum cofactor (Moco). The two pathways intersect at several points, but a scarcity of mutants has hindered studies to better understand these links. We screened a collection of sirtinol-resistant Arabidopsis thaliana mutants for lines with decreased activities of cytosolic FeS enzymes and Moco enzymes. We identified a new mutant allele of ATM3 (ABC transporter of the mitochondria 3), encoding the ATP-binding cassette transporter of the mitochondria 3 (systematic name ABCB25), confirming the previously reported role of ATM3 in both FeS cluster and Moco biosynthesis. We also identified a mutant allele in CNX2, cofactor of nitrate reductase and xanthine dehydrogenase 2, encoding GTP 3′,8-cyclase, the first step in Moco biosynthesis which is localized in the mitochondria. A single-nucleotide polymorphism in cnx2-2 leads to substitution of Arg88 with Gln in the N-terminal FeS cluster-binding motif. cnx2-2 plants are small and chlorotic, with severely decreased Moco enzyme activities, but they performed better than a cnx2-1 knockout mutant, which could only survive with ammonia as a nitrogen source. Measurement of cyclic pyranopterin monophosphate (cPMP) levels by LC–MS/MS showed that this Moco intermediate was below the limit of detection in both cnx2-1 and cnx2-2, and accumulated more than 10-fold in seedlings mutated in the downstream gene CNX5. Interestingly, atm3-1 mutants had less cPMP than wild type, correlating with previous reports of a similar decrease in nitrate reductase activity. Taken together, our data functionally characterize CNX2 and suggest that ATM3 is indirectly required for cPMP synthesis.

Item Type:Articles
Additional Information:Funding: I.K. was funded by a Dean’s studentship from the University of East Anglia and an Institute Development Grant from the John Innes Centre [CX410-J11A]. A.M. was funded by a John Innes Foundation studentship. The LC–MS/MS analysis was supported by a Biotechnology and Biological Sciences Research Council (BBSRC) Institute Strategic Grant [BB/P012523/1].
Glasgow Author(s) Enlighten ID:MacLean, Dr Andrew
Authors: Kruse, I., MacLean, A. E., Hill, L., and Balk, J.
College/School:College of Medical Veterinary and Life Sciences > School of Infection & Immunity
Journal Name:Biochemical Journal
Publisher:Portland Press
ISSN (Online):1470-8728
Published Online:15 December 2017
Copyright Holders:Copyright © 2018 The Authors
First Published:First published in Biochemical Journal 475(2):495-509
Publisher Policy:Reproduced under a Creative Commons license

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