Molecular cloning and functional analysis of the phosphomannomutase (PMM) gene from Dendrobium officinale and evidence for the involvement of an abiotic stress response during germination

Phosphomannomutase (PMM, EC 5.4.2.8) catalyzes the interconversion of mannose-6-phosphate to mannose-1-phosphate, the precursor for the synthesis of GDP-mannose. In this study, the complementary DNA (cDNA) of the Phosphomannomutase (PMM) gene was initially cloned from Dendrobium officinale by RACE method. Transient transform result showed that the DoPMM protein was localized in the cytoplasm. The DoPMM gene was highly expressed in the stems of D. officinale both in vegetative and reproductive developmental stages. The putative promoter was cloned by TAIL-PCR and used for searched cis-elements. Stress-related cis-elements like ABRE, TCA-element, and MBS were found in the promoter regions. The DoPMM gene was up-regulated after treatment with abscisic acid, salicylic acid, cold, polyethylene glycol, and NaCl. The total ascorbic acid (AsA) and polysaccharide content in all of the 35S::DoPMM Arabidopsis thaliana transgenic lines #1, #2, and #5 showed a 40, 39, and 31% increase in AsA and a 77, 22, and 39% increase in polysaccharides, respectively more than wild-type (WT) levels. All three 35S::DoPMM transgenic lines exhibited a higher germination percentage than WT plants when seeded on half-strength MS medium supplemented with 150 mM NaCl or 300 mM mannitol. These results provide genetic evidence for the involvement of PMM genes in the biosynthesis of AsA and polysaccharides and the mediation of PMM genes in abiotic stress tolerance during seed germination in A. thaliana.