Isolation and characterization of a myo-inositol 1-phosphate synthase cDNA from developing sesame (Sesamum indicum L.) seeds:: functional and differential expression, and salt-induced transcription during germination

A cDNA (SeMIPS1) encoding myo-inositol 1-phosphate synthase (EC 5.5.1.4) (MIPS) has been characterized from sesame (Sesamum indicum L. cv. Dan-Baek) seeds and its functional expression analyzed. The SeMIPS1 protein was highly homologous with those from other plant species (88-94%), while a much lower degree of sequence homology (53-62%) was found with other organisms such as humans, mouse, algae, yeast, Drosophila, bacteria and other prokaryotes. A yeast-based complementation assay in yeast mutants containing a disrupted INO1 gene for yeast MIPS confirmed that the SeMIPS1 gene encodes a functional MIPS. Phylogenetic analysis suggested that the SeMIPS1 gene diverged as a different subfamily or family member. Southern hybridization revealed several copies of the SeMIPS1 gene present in the sesame genome and northern blotting indicated that expression of the SeMIPS1 gene may be organ specific. Salt stress during sesame seed germination had an adverse influence on transcription of SeMIPS1 and greatly reduced transcript levels as the duration of exposure to a saline environment increased and NaCl concentration increased. Germination initiation of sesame seeds was severely delayed as NaCl level increased. These results suggest that expression of SeMIPS1 is down-regulated by salt stress during sesame seed germination.