Characterization of -inositol oxygenase from rice (): influence of salinity stress in different rice cultivars.

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-inositol oxygenase (MIOX), the only catabolic enzyme of the inositol pathway, catalyzes conversion of -inositol to D-GlcA (glucuronic acid). The present study encompasses bioinformatic analysis of gene across phylogenetically related plant lineages and representative animal groups. Comparative motif analysis of the gene(s) across various plant groups suggested existence of abiotic- stress related -acting elements such as, DRE, MYB, MYC, STRE, MeJa among others. A detailed analysis revealed a single isoform of gene, located in chromosome 6 of rice () with an open reading frame of 938 bp coding for 308 amino acids producing a protein of ~ 35 kD. Secondary structure prediction of the protein gave the predicted number of 144 alpha helices and 154 random coils. The three-dimensional structure suggested it to be a monomeric protein with a single domain. Bacterial overexpression of the protein, purification and enzyme assay showed optimal catalytic activity at pH 7.5-8 at an optimal temperature of 37 °C with Michaelis constant of 40.92 mM. The range of Km was determined as 22.74-28.7 mM and the range of Vmax was calculated as 3.51-3.6 µM/min, respectively. Four salt-tolerant and salt-sensitive rice cultivars displayed differential gene expression of at different time points in different tissues under salinity and drought stress as observed from qRT-PCR data, microarray results and protein expression profile in immunoblot analysis. Gel volumetric analysis confirmed a very high expression of in roots and leaves on 7th day following germination. Microarray data showed high expression of at all developmental stages including seedling growth and reproduction. These data suggest that OsMIOX might have a role to play in rice abiotic stress responses mediated through the -inositol oxidation pathway.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-023-01340-6.