d-Amino Acids in Plants: Sources, Metabolism, and Functions

Abstract

Although plants are permanently exposed to D-amino acids (D-AAs) in the rhizosphere, these compounds were for a long time regarded as generally detrimental, due to their inhibitory effects on plant growth. Recent studies showed that this statement needs a critical revision. There were several reports of active uptake by and transport of D-AAs in plants, leading to the question whether these processes happened just as side reactions or even on purpose. The identification and characterization of various transporter proteins and enzymes in plants with considerable affinities or specificities for D-AAs also pointed in the direction of their targeted uptake and utilization. This attracted more interest, as D-AAs were shown to be involved in different physiological processes in plants. Especially, the recent characterization of D-AA stimulated ethylene production in Arabidopsis thaliana revealed for the first time a physiological function for a specific D-AA and its metabolizing enzyme in plants. This finding opened the question regarding the physiological or developmental contexts in which D-AA stimulated ethylene synthesis are involved in. This question and the ones about the transport characteristics of D-AAs, their metabolism, and their different physiological effects, are the focus of this review.

Plant Growth-Promoting Endophytic Bacillus Aryabhattai Triggers Novel Genes to Induce Plant Growth

“…Although plants are constantly exposed to D-amino acids (D-AAs) in the rhizosphere, these compounds have inhibitory effects on plant growth. A recent characterization of D-AA-stimulated ethylene production in Arabidopsis showed the physiological function of a speci c D-AA and its metabolizing enzyme in plants [51]. Most likely, the regulation of plant D-AA content could in uence the composition of the rhizosphere [52].…”

d‐Amino acids in biological systems

“…DADs, which catalyze the dehydrogenation of D‐amino acids to corresponding imino acids, also were found in plants 59 . Important aspects of D‐amino acids in plants have been reviewed recently 60 …”

Endophytic bacterium Bacillus aryabhattai induces novel transcriptomic changes to stimulate plant growth

“…Contradictorily, the expression of the D-hydantoinase gene was induced in the bacterium during its interaction with the plant. These D-amino acids (D-AAs) exert a growth-inhibiting effect on plants [62][63][64]. The exogenous administration of various D-AAs to growth media has a deleterious or favorable effect on the growth and development of many plant species, and these effects depend on the D-AAs used [63,65].…”

“…These D-amino acids (D-AAs) exert a growth-inhibiting effect on plants [62][63][64]. The exogenous administration of various D-AAs to growth media has a deleterious or favorable effect on the growth and development of many plant species, and these effects depend on the D-AAs used [63,65]. However, the mechanism responsible for the finding that its expression is correlated with growth stimulation but not growth inhibition.…”