Elucidating the role of Inositol monophosphatases gene family in abiotic stress management

Apart from many crucial roles in cellular processes and signaling pathways, myo-inositol is also considered as an important osmoprotectant, which is directly involved in abiotic stress management in plants. Myo-inositol monophosphatase (IMP) catalyses the conversion of inositol 1-phosphate to myo-inositol, the second step in inositol biosynthesis. We have isolated IMP (CaIMP) from drought tolerant legume Chickpea (Cicer arietinum). The stress-induced increased accumulation of inositol has been reported in chickpea; however, the role and regulation of IMP is not well defined in response to stress.

We have demonstrated the significance of IMP in abiotic stress tolerance and thus explained its role in improving seed germination and plant growth under variety of stresses including drought and salt stress. Biochemical study revealed that CaIMP encodes a lithium-sensitive phosphatase enzyme with broad substrate specificity, it has been found to be implicated in both inositol and ascorbate biosynthesis. Apart from its main substrate Inositol 1-P and Galactose 1-P, CaIMP was also able to hydrolyze other substrates like Phytate, Fructose 1,6 bis-P. Our results indicate that, CaIMP possibly link various metabolic pathways. The transcript level of IMP has also been studied and found to be increased in different abiotic stresses.

We have also identified two IMP like proteins from chickpea; CaIMPL1 and CaIMPL2. Not much is known about the functions of IMPL. We have checked transcript level of both CaIMPL1 and CaIMPL2 under different abiotic stresses and hormone treatments in chickpea. Interestingly, differential expression of CaIMPL1 and CaIMPL2 were observed under different abiotic stresses. Similar to CaIMP, it also showed induction by ABA treatment. Our work also signifies the role of CaIMPL2 in Histidine pathway as it was able to catalyze the dephosphorylation of Histidinol 1-P, however IMPL1 was mostly involved in the hydrolysis of D-Ins 3-P and D Gal 1-P. Given the relation between IMP, IMPL1 and IMPL2, the difference in substrate specificity among these highly homologous enzymes suggests that the genes encoding these enzymes have diverged evolutionarily. Also, we have shown that broad substrate specificity of CaIMP enzyme is because of presence of very peculiar flexible loop structure and dynamic nature of active site.