Biochemical characterization and spatio-temporal expression of myo-inositol oxygenase (MIOX) from wheat (Triticum aestivum L.)

Myo-inositol oxygenase (MIOX) catalyzes the conversion of myo-inositol into d-glucuronic acid. The present study demonstrates isolation of MIOX cDNA (TaMIOX) from wheat (Triticum aestivum L.) with open reading frame of 912 bp encoding 303 amino acid polypeptides with a molecular mass of 35.2 kDa. Phylogenetic analysis of TaMIOX across kingdoms confirmed the close relationship with Triticum urartu and Aegilops tauschii. Secondary structure of TaMIOX consists of α-helixes (42.9%), β-turns (7.26%) joined by extended strands (14.85%), and 37 random coils (34.94%). Three-dimensional structure of TaMIOX suggested its close functional and structural resemblance with known MIOX. Catalytic activity of the purified TaMIOX is 3.47 μkatal at pH 8.0 and 35 °C with Michaelis constant 5.6 mM. Differential expression pattern of TaMIOX was observed in leaves, root, stem, seed and seed developmental stages. Leaves showed a significantly higher transcript accumulation followed by root, stem and seed. Expression of TaMIOX during seed development stages showed higher expression at later stage and suggested that expression of TaMIOX was significantly higher in endosperm as compared with aleurone. The exogenous application of myo-inositol enhanced the expression of TaMIOX in leaves and roots suggested myo-inositol acts as an inducer for the TaMIOX expression. The present study reports molecular, structural and biochemical characterizations of MIOX in wheat which might play an important role in myo-inositol oxidation pathway.