Regulation of Cell-Specific Inositol Metabolism and Transport in Plant Salinity Tolerance

Abstract

myo-Inositol and its derivatives are commonly studied with respect to cell signaling and membrane biogenesis, but they also participate in responses to salinity in animals and plants. In this study, we focused on L-myo-inositol 1-phosphate synthase (INPS), which commits carbon to de novo synthesis, and myo-inositol O-methyltransferase (IMT), which uses myo-inositol for stress-induced accumulation of a methylinositol, D-ononitol. The Imt and Inps promoters are transcriptionally controlled. We determined that the transcription rates, transcript levels, and protein abundance are correlated. During normal growth, INPS is present in all cells, but IMT is repressed. After salinity stress, the amount of INPS was enhanced in leaves but repressed in roots. IMT was induced in all cell types. The absence of myo-inositol synthesis in roots is compensated by inositol/ononitol transport in the phloem. The mobilization of photosynthate through myo-inositol translocation links root metabolism to photosynthesis. Our model integrates the transcriptional control of a specialized metabolic pathway with physiological reactions in different tissues. The tissue-specific differential regulation of INPS, which leads to a gradient of myo-inositol synthesis, supports root growth and sodium uptake. By inducing expression of IMT and increasing myo-inositol synthesis, metabolic end products accumulate, facilitating sodium sequestration and protecting photosynthesis.

A Novel Salt-tolerant l-myo-Inositol-1-phosphate Synthase from Porteresia coarctata (Roxb.) Tateoka, a Halophytic Wild Rice

“…8). Increased synthesis of inositol and its transport has been shown previously to play a major role in sequestration of sodium ions and maintenance of photosynthetic competence during salt stress (42,46). A protective role for inositol in maintaining the photosynthetic efficiency of the plants, as demonstrated previously for other osmolytes like glycine-betaine or proline (43,(47)(48), may also be inferred from such results.…”

“…Regulation of inositol pathway in relation to salt stress has also been studied earlier (21,42). In a facultative halophyte-like Mesembryamthemum crystallinum, a coordinate transcriptional induction of INO1 and the inositol methyltransferase (IMT) gene(s) under salt environment for production of both inositol and its methylated derivative, pinitol has been documented (49).…”

“…We have chosen the enzyme MIPS, which is conserved across evolutionarily diverse taxa (4,12), produces inositol, and is known to function in varied biochemical activities and also during stress in both prokaryotic and eukaryotic organisms (3,(41)(42)(43)(44)(45). Among the 65 INO1 genes known (12), the INO1 from Archaeoglobus fulgidis (11) has been shown to code for a thermotolerant protein, the only stress-tolerant MIPS so far reported.…”

Arabidopsis INOSITOL TRANSPORTER2 Mediates H+ Symport of Different Inositol Epimers and Derivatives across the Plasma Membrane

“…In leaves of unstressed soybean (Glycine max), for example, concentrations of pinitol (3-O-methyl-chiroinositol) can be 2-fold higher than the combined concentrations of Suc, all monosaccharides, and myoinositol (Smith and Phillips, 1982;Streeter et al, 2001). This already high concentration is further increased in droughtstressed plants, underlining the important role of unmethylated and methylated inositols as osmoprotectants (Thomas and Bohnert, 1993;Sheveleva et al, 1997;Nelson et al, 1998;Hasegawa et al, 2000;Streeter et al, 2001;Murakeö zy et al, 2003).…”

Toxicological effects of environmentally relevant lead and zinc in halophyte Suaeda salsa by NMR-based metabolomics

“…Among the selected enzymes, Myo-inositol-1-phosphate synthase (INPS, BE644574) is the key enzyme of Myo-inositol (Ins) biosynthesis. It has been confirmed that INPS regulates the pathway of Ins biosynthesis (Nelson et al, 1998), which is a specific pathway in salt tolerance in the common ice plant (Vernon and Bohnert, 1992), and its expression can be feedback inhibited by myo-inositol. In higher plants, betaine is synthesized by oxidation of choline: cholinebetaine aldehyde-betaine.…”