Amino Acid Catabolism in Plants

authored by
Tatjana M. Hildebrandt
supervised by
A. Harvey Millar

Amino acids are among the most versatile compounds in plants performing

diverse functions within proteins as well as individually. The

publications constituting this habilitation thesis focus on different

aspects of amino acid catabolism. Not all of the biochemical pathways

catalyzing degradation of the twenty proteinogenic amino acids in plants

are known, and annotation of amino acid catabolic enzymes in databases

and pathway maps is still insufficient for comprehensive evaluation of

proteomics or transcriptomics datasets. Thus, a manually assembled

pathway map covering 136 reactions involved in amino acid related

pathways is presented and used for reevaluation of already published as

well as interpretation of new omics datasets. This approach clearly

defines gaps in the present knowledge and at the same time postulates

candidate proteins for unknown reactions as a starting point for further

investigation. In addition, it provides insight into the different

metabolic functions of amino acid catabolism and their significance

during abiotic and biotic stress response.


A major topic of the work presented here is cysteine catabolism.

Cysteine in addition to the amino group also contains a thiol moiety and

therefore represents an intersection of carbon, nitrogen and sulfur

metabolism. The degradation of cysteine via different enzymatic routes

releases reduced sulfur in the form of sulfide or persulfide, which act

as signaling molecules and can be further metabolized either by

reincorporation into cysteine or by oxidation. This thesis describes a

mitochondrial cysteine catabolic pathway that oxidizes the thiol group

catalyzed by the sulfur dioxygenase ETHE1. In plants, this pathway is

essential during early embryo development and also required for energy

metabolism during low light availability. Mutations in the ETHE1 gene in

humans cause the metabolic disease ethylmalonic encephalopathy, which

is characterized by rapidly progressive encephalopathy, chronic

diarrhea, and peripheral microangio¬pathy caused by accumulation of

toxic sulfide levels. These symptoms can be relieved by combined

treatment with a bactericide that represses sulfide production by

intestinal anaerobes and N-acetylcysteine as a precursor for

glutathione, which can act as a buffer for reduced sulfur.

Institute of Plant Genetics
Habilitation treatise
No. of pages
Publication date
Publication status
ASJC Scopus subject areas
Molecular Biology, Plant Science
Sustainable Development Goals
SDG 3 - Good Health and Well-being
Electronic version(s) (Access: Open)