Rhizosphere Bacterium Rhodococcus sp. P1Y Metabolizes Abscisic Acid to Form Dehydrovomifoliol

Abstract

The phytohormone abscisic acid (ABA) plays an important role in plant growth and in response to abiotic stress factors. At the same time, its accumulation in soil can negatively affect seed germination, inhibit root growth and increase plant sensitivity to pathogens. ABA is an inert compound resistant to spontaneous hydrolysis and its biological transformation is scarcely understood. Recently, the strain Rhodococcus sp. P1Y was described as a rhizosphere bacterium assimilating ABA as a sole carbon source in batch culture and affecting ABA concentrations in plant roots. In this work, the intermediate product of ABA decomposition by this bacterium was isolated and purified by preparative HPLC techniques. Proof that this compound belongs to ABA derivatives was carried out by measuring the molar radioactivity of the conversion products of this phytohormone labeled with tritium. The chemical structure of this compound was determined by instrumental techniques including high-resolution mass spectrometry, NMR spectrometry, FTIR and UV spectroscopies. As a result, the metabolite was identified as (4RS)-4-hydroxy-3,5,5-trimethyl-4-[(E)-3-oxobut-1-enyl]cyclohex-2-en-1-one (dehydrovomifoliol). Based on the data obtained, it was concluded that the pathway of bacterial degradation and assimilation of ABA begins with a gradual shortening of the acyl part of the molecule.

Growth-Promoting Effect of Rhizobacterium (Bacillus subtilis IB22) in Salt-Stressed Barley Depends on Abscisic Acid Accumulation in the Roots

“…Abscisic acid (ABA) was less studied, although it is the latter hormone that is most involved in plants’ stress responses [ 14 ]. Nevertheless, there are reports showing the ability of bacteria either to produce [ 15 ] or catabolize ABA [ 16 , 17 ] and influence the concentration of this hormone in plants [ 18 , 19 ]. Production of ABA by plants has been shown to be important for plant response to PGPR [ 20 ]: unlike wild-type tomato plants, in which PGPR stimulated growth, bacteria inhibited the growth of ABA-deficient mutant plants.…”

Isolation and Characterization of 1-Hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexene-1-acetic Acid, a Metabolite in Bacterial Transformation of Abscisic Acid

“…P1Y on the minimal medium with ABA was accompanied by the degradation of this phytohormone and the accumulation of additional metabolites in the culture liquid. HPLC-MS revealed two putative metabolites, one of which was purified and identified as dehydrovomifoliol [ 46 ]. In the present work, we increased the cultivation time after the addition of ABA from 2 to 4 h, which increased the accumulation of the second compound ( Figure 1 , compound with a retention time (RT) of 4.8 min) in the culture liquid with a simultaneous decrease in the content of dehydrovomifoliol and ABA ( Figure 1 , compounds with RT of 5.4 and 6.3 min, respectively).…”

“…For FTIR spectroscopic measurements, a sample of the isolated and purified compound (~1 mg) was dissolved in a minimal volume (~10 μL) of MilliQ water, placed (using a microsyringe) as a thin film on a clean flat ZnSe disk (CVD-ZnSe, “R’AIN Optics”, Dzerzhinsk, Russia; ø 1 cm, thickness 0.2 cm) and dried in a drying cabinet at 45 °C (~20 h). Transmission FTIR spectroscopic measurements were performed on a Nicolet 6700 FTIR spectrometer (Thermo Electron Corporation, Beverly, MA, USA; DTGS detector; KBr beam splitter) as reported earlier [ 46 ] (with a total of 64 scans (resolution 4 cm −1 ) against the ZnSe disk background; spectra were manipulated using the OMNIC software (version 8.2.0.387) supplied by the manufacturer of the spectrometer). The baseline was corrected using the “automatic baseline correct” function, and the spectra were smoothed using the standard “automatic smooth” function of the software which uses the Savitsky–Golay algorithm (95-point moving second-degree polynomial).…”

“…We have also shown that Rhodococcus sp. P1Y is able to shorten the acyl moiety of the ABA molecule to form dehydrovomifoliol [ 46 ]. This work is devoted to a further study of ABA catabolism in this bacterial species and presents a new bacterial metabolite.…”

Phytohormones 2020

“…The next [ 5 ] article of the issue addresses another plant hormone (abscisic acid, ABA), which plays an important role in plant growth and in response to abiotic stress factors. The authors assert that its accumulation in soil can negatively affect seed germination and plant growth.…”