Cloning, functional expression and characterization of Mesorhizobium loti arylamine N‐acetyltransferases: rhizobial symbiosis supplies leguminous plants with the xenobiotic N‐acetylation pathway

Abstract

SummaryArylamine N -acetyltransferases (NATs) are xenobiotic-metabolizing enzymes involved in the detoxification of numerous aromatic chemicals. The NATdependent N-acetylation pathway has not previously been detected in plants. We demonstrate here the occurrence of the NAT-dependent pathway in leguminous plants, due to symbiosis with Mesorhizobium loti . We cloned two NAT enzymes from M. loti and showed that these two recombinant enzymes catalysed the N-acetylation of several known NAT substrates, including aniline-derived pesticide residues. We also demonstrate the existence of a functional NAT-dependent acetylation pathway in the root nodules of Lotus japonicus inoculated with M. loti . M. loti is the first non-eukaryotic organism shown to express two catalytically active NAT isoforms. This work also provides the first evidence for acquisition of a xenobiotic detoxification pathway by a plant through symbiosis with a soil microbe.

An Acetyltransferase Conferring Tolerance to Toxic Aromatic Amine Chemicals

“…The catalytic efficiency of PaNat1 with 3,4-DCA was 2.5 times higher and that of PaNat2 was five times higher than that of the Pseudomonas aeruginosa NAT, which is currently considered to be the most efficient NAT enzyme ever described, particularly with 3,4-DCA (29). When compared with the two NAT isoforms from the plant symbiotic bacterium Mesorhizobium loti, the catalytic efficiency toward 3,4-DCA by PaNAT2 (k cat /K m ϭ 17,400 M Ϫ1 ⅐s Ϫ1 ) was 220 and 120 times higher than that of M. loti NAT1 and M. loti NAT2, respectively (14).…”

“…Certain fungi and bacteria have nonetheless been shown to biotransform 3,4-DCA to its acetylated form (19,34). In the bacterium M. loti, a NAT isoform has been shown to acetylate 3,4-DCA (14). In plants, glucosylation of 3,4-DCA was described, but this pathway was considered as non-effective at detoxifying this AA (35).…”

“…An antibody raised against the Salmonella typhimurium NAT enzyme was used to detect the purified recombinant PaNat1 and PaNat2 proteins (14).…”

“…Four well known fungal species (Fusarium graminearum, Phycomyces blakesleeanus, P. anserina, and Rhizopus oryzae) from different ecosystems, for which complete genome sequences were available, were screened for radial growth in the presence of three toxic AA: 3,4-DCA (pesticide residue), 2-AF (carcinogen), and 4-BOA (chemical intermediate) (14). The growth of R. oryzae and P. blakesleeanus was almost completely abolished by these three AA at concentrations of 100 -250 M in standard minimal growth medium.…”

Fungi as a promising tool for bioremediation of soils contaminated with aromatic amines, a major class of pollutants

“…Most studies have focused on conversion of 3,4-DCA into its acetylated form. First, it has been shown that acetylated 3,4-DCA is less toxic than 3,4-DCA; second, some soil bacteria and fungal strains acetylate 3,4-DCA 12,13 . Although aniline derivatives undergo complex transformations in soils, these studies open up new possibilities in bioremediation.…”