D-amino acids are the D stereoisomers of common L-amino acids found in
proteins. In the past two decades, the occurrence of D-amino acids in
plants has been reported and circumstantial evidence for a role in
several processes has been provided, including the interaction with soil
microorganisms or an interference with cellular signalling. However,
examples are relatively scarce and D-amino acids can also be
detrimental, some of them inhibiting growth and development. Thus, the
persistence of a D-amino acid metabolism in plants is rather surprising
and evolutive origins of D-amino acid metabolism is presently unclear.
Systemic analysis of sequences associated with enzymes of D-amino acid
metabolism shows that they are not simply inherited from cyanobacterial
metabolism. In effect, the history of enzymes of plant D-amino acid
metabolism likely involves several steps, cellular compartments, gene
transfers and losses. Regardless of evolutive steps, enzymes of D-amino
acid metabolism like D-amino acid transferases or racemases have been
kept by higher plants and not simply eliminated, hence it is likely that
they fulfil important metabolic roles, which can be illustrated with
serine, tryptophan, and folate metabolism. We suggest that D-amino acid
metabolism was perhaps crucial to support metabolic functions required
during land plants evolution.