Capacities and constraints of amino acid utilization in Arabidopsis

Abstract

Various amino acids, including both L- and D-enantiomers, may be present in soils, and recent studies have indicated that plants may access such nitrogen (N) forms. Here, the capacity of Arabidopsis to utilize different L- and D-amino acids is investigated and the constraints on this process are explored. Mutants defective in the lysine histidine transporter 1 (LHT1) and transgenic plants overexpressing LHT1 as well as plants expressing D-amino acid-metabolizing enzymes, were used in studies of uptake and growth on various N forms. Arabidopsis absorbed all tested N-forms, but D-enantiomers at lower rates than L-forms. Several L- but no D-forms were effective as N sources. Plants deficient in LHT1 displayed strong growth reductions and plants overexpressing LHT1 showed strong growth enhancement when N was supplied as amino acids, in particular when these were supplied at low concentrations. Several D- amino acids inhibited growth of wild-type plants, while transgenic Arabidopsis-expressing genes encoding D-amino acid-metabolizing enzymes could efficiently utilize such compounds for growth. These results suggest that several amino acids, and in particular L-Gln and L-Asn, promote growth of Arabidopsis, and increased expression of specific amino acid transporters enhances growth on amino acids. The efficiency by which transgenic plants exploit D-amino acids illustrates how plants can be engineered to utilize specific N sources otherwise inaccessible to them.

Lysine catabolism, amino acid transport, and systemic acquired resistance

“…This amino acid therefore can even shape root morphology: in plants overexpressing or lacking the Lys-transporting amino acid transporter CATIONIC AMINO ACID TRANSPORTER1 (CAT1), the lateral root density was increased by Lys and affected in the mutants. 5 The inhibitory effects of Asp-derived AAs are largely consistent with the results from Arabidopsis seedlings at higher basal N supply, 6,7 and these are at least partially physiologically explained by the complex feedback inhibition that these AAs impose on the primary biosynthesis of essential amino acids. Lysine is an essential amino acid for human nutrition, which is generally low in cereal diets.…”

Analysis of Nitrogen Utilization Capability during the Proliferation and Maturation Phases of Norway Spruce (Picea abies (L.) H.Karst.) Somatic Embryogenesis

“…For Picea glauca, four times higher fresh weight increase on initiation medium was observed when L-glutamine was the sole source of nitrogen compared to growth on ammonium nitrate [30]. The increase in proliferation rates observed in media containing NO 3 in addition to Gln could be due to the release of additional L-glutamine from metabolized nitrate, or by nitrate functioning as a growth promoting signal [31].…”

Amino Acid Homeostasis Modulates Salicylic Acid–Associated Redox Status and Defense Responses inArabidopsis

“…Although LHT1 was previously reported to be a broad-spectrum amino acid transporter (Hirner et al, 2006;Svennerstam et al, 2007;Forsum et al, 2008), these abundant amino acids are possibly the main physiological substrates of LHT1. Growth assays on D-amino acids as the sole nitrogen source showed that the root growth of the lht1 mutant was less sensitive to the toxic D-Gln and D-Asn, suggesting that Gln and Asn are preferred substrates of LHT1.…”

“…In view of these contradictory results, we adapted an assay that uses D-enantiomeric amino acids (Erikson et al, 2004). D-enantiomers are generally toxic to plant cells but are thought to be taken up by the same transporters and with similar kinetics as their L-form counterparts (Erikson et al, 2004;Svennerstam et al, 2007;Forsum et al, 2008). Our results showed that, although both lht1 and wild-type seeds germinated well on complete Murashige and Skoog (MS) medium supplemented with a range of concentrations of D-amino acids, except for D-Cys, significant inhibition of root and leaf development were observed, indicating that all tested D-enantiomers are toxic to Arabidopsis (see Supplemental Figure 9 online).…”