Molecular cloning and characterization of a cDNA encoding kiwifruit L-myo-inositol-1-phosphate synthase, a key gene of inositol formation

l-myo-inositol-1-phosphate synthase (MIPS; EC 5.5.1.4) is the key enzyme involved in de novo synthesis of myo-inositol, leading to numerous cellular functions. We isolated an open reading frame of Actinidia deliciosa MIPS (AdMIPS), which is 1,533 bp long and codes for 510 amino acids, with a predicted molecular weight of 56.3 kDa. Sequence analysis revealed its high similarity with MIPS proteins from other organisms. Gene expression and enzyme activity were highest in flower and young fruit. Transcription of AdMIPS was also detected in other tissues. Moderate drought drastically induced expression in the leaves whereas salinity stress induced transcription and enzyme activity in the leaves, phloem, and roots with different degrees. However, a longer period of saline exposure suppressed both expression and enzyme activity in all sampled tissues, indicating that AdMIPS is salt-sensitive.