Altered metabolism of chloroplastic NAD kinase-overexpressing Arabidopsis in response to magnesium sulfate supplementation.

Nicotinamide adenine dinucleotide (NAD)/NAD phosphate (NADPH) is essential for numerous redox reactions and serve as co-factors in multiple metabolic processes in all organisms. NAD kinase (NADK) is an enzyme involved in the synthesis of NADP+ from NAD+ and ATP. Arabidopsis NADK2 (AtNADK2) is a chloroplast-localizing enzyme that provides recipients of reducing power in photosynthetic electron transfer. When Arabidopsis plants were grown on MS medium supplemented with 5 mM MgSO4, an AtNADK2-overexpressing line exhibited higher glutathione and total sulfur accumulation than control plants. Metabolomic analysis of major amino acids and organic acids using capillary electrophoresis-mass spectrometry demonstrated that overexpression of AtNADK2 affected a range of metabolic processes in response to MgSO4 supplementation.

Ralfuranones contribute to mushroom-type biofilm formation by Ralstonia solanacearum strain OE1-1.

After invasion into intercellular spaces of tomato plants, the soil-borne, plant-pathogenic Ralstonia solanacearum strain OE1-1 forms mushroom-shaped biofilms (mushroom-type biofilms, mBFs) on tomato cells, leading to its virulence. The strain OE1-1 produces aryl-furanone secondary metabolites, ralfuranones (A, B, J, K and L), dependent on the quorum sensing (QS) system, with methyl 3-hydroxymyristate (3-OH MAME) synthesized by PhcB as a QS signal. Ralfuranones are associated with the feedback loop of the QS system. A ralfuranone productivity-deficient mutant (ΔralA) exhibited significantly reduced growth in intercellular spaces compared with strain OE1-1, losing its virulence. To analyse the function of ralfuranones in mBF formation by OE1-1 cells, we observed cell aggregates of R. solanacearum strains statically incubated in tomato apoplast fluids on filters under a scanning electron microscope. The ΔralA strain formed significantly fewer microcolonies and mBFs than strain OE1-1. Supplementation of ralfuranones A, B, J and K, but not L, significantly enhanced the development of mBF formation by ΔralA. Furthermore, a phcB- and ralA-deleted mutant (ΔphcB/ralA) exhibited less formation of mBFs than OE1-1, although a QS-deficient, phcB-deleted mutant formed mBFs similar to OE1-1. Supplementation with 3-OH MAME significantly reduced the formation of mBFs by ΔphcB/ralA. The application of each ralfuranone significantly increased the formation of mBFs by ΔphcB/ralA supplied with 3-OH MAME. Together, our findings indicate that ralfuranones are implicated not only in the development of mBFs by strain OE1-1, but also in the suppression of QS-mediated negative regulation of mBF formation.