title: Metabolic engineering of the chloroplast genome reveals that the yeast ArDH gene confers enhanced tolerance to salinity and drought in plants.
abstract: Osmoprotectants stabilize proteins and membranes against the denaturing effect of high concentrations of salts and other harmful solutes. In yeast, arabitol dehydrogenase (ArDH) reduces D-ribulose to D-arabitol where D-ribulose is derived by dephosphorylating D-ribulose-5-PO4 in the oxidized pentose pathway. Osmotolerance in plants could be developed through metabolic engineering of chloroplast genome by introducing genes encoding polyols since chloroplasts offer high level transgene expression and containment. Here, we report that ArDH expression in tobacco chloroplasts confers tolerance to NaCl (up to 400 mM). Transgenic plants compared to wild type (WT) survived for only 4-5 weeks on 400 mM NaCl whereas plants remained green and grew normal on concentrations up to 350 mM NaCl. Further, a-week-old seedlings were also challenged with poly ethylene glycol (PEG, up to 6%) in the liquid medium, considering that membranes and proteins are protected under stress conditions due to accumulation of arabitol in chloroplasts. Seedlings were tolerant to 6% PEG, suggesting that ARDH enzyme maintains integrity of membranes in chloroplasts under drought conditions via metabolic engineering. Hence, the gene could be expressed in agronomic plants to withstand abiotic stresses.
authors.affiliation: Center of Agricultural Biochemistry and Biotechnology, University of Agriculture, Faisalabad Pakistan.
authors.forename: Muhammad Sarwar
authors.initials: MS
authors.lastname: Khan
authors.affiliation: National Institute for Biotechnology and Genetic Eningeering, Faisalabad Pakistan.
authors.forename: Benish
authors.initials: B
authors.lastname: Kanwal
authors.affiliation: Agricultural Biotechnology Research Institute - Ayub Agricultural Research Institute, Faisalabad Pakistan.
authors.forename: Shahid
authors.initials: S
authors.lastname: Nazir
keywords: arabitol dehydrogenase; chloroplast transformation; osmoprotectants; salt and draght tolerance