d-myo-Inositol-3-Phosphate Affects Phosphatidylinositol-Mediated Endomembrane Function inArabidopsisand Is Essential for Auxin-Regulated Embryogenesis  

Abstract

In animal cells, myo-inositol is an important regulatory molecule in several physiological and biochemical processes, including signal transduction and membrane biogenesis. However, the fundamental biological functions of myo-inositol are still far from clear in plants. Here, we report the genetic characterization of three Arabidopsis thaliana genes encoding D-myo-inositol-3-phosphate synthase (MIPS), which catalyzes the rate-limiting step in de novo synthesis of myo-inositol. Each of the three MIPS genes rescued the yeast ino1 mutant, which is defective in yeast MIPS gene INO1, and they had different dynamic expression patterns during Arabidopsis embryo development. Although single mips mutants showed no obvious phenotypes, the mips1 mips2 double mutant and the mips1 mips2 mips3 triple mutant were embryo lethal, whereas the mips1 mips3 and mips1 mips2 +/2 double mutants had abnormal embryos. The mips phenotypes resembled those of auxin mutants. Indeed, the double and triple mips mutants displayed abnormal expression patterns of DR5:green fluorescent protein, an auxin-responsive fusion protein, and they had altered PIN1 subcellular localization. Also, membrane trafficking was affected in mips1 mips3. Interestingly, overexpression of PHOSPHATIDYLINOSITOL SYNTHASE2, which converts myoinositol to membrane phosphatidylinositol (PtdIns), largely rescued the cotyledon and endomembrane defects in mips1 mips3. We conclude that myo-inositol serves as the main substrate for synthesizing PtdIns and phosphatidylinositides, which are essential for endomembrane structure and trafficking and thus for auxin-regulated embryogenesis.

The Polyadenylation Factor Subunit CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR30: A Key Factor of Programmed Cell Death and a Regulator of Immunity in Arabidopsis

“…The mips1 mutants also display defects in primary root development (Luo et al, 2011), but the oxt6 mutation did not rescue this mips1 phenotype (Fig. 2C), indicating that CPSF30 is specifically involved in the cell death-related defects of the mips1 mutant but not in other cellular processes requiring MI.…”

“…Another striking phenotype of the mips1 mutant was the alterations in cotyledon morphology characterized by irregular margins and altered vascular patterning (Meng et al, 2009;Chen and Xiong, 2010;Donahue et al, 2010;Luo et al, 2011). To investigate whether this abnormality, like lesion formation, also was suppressed in the oxt6 mutant background, we examined cotyledon development in the mips1 oxt6 double mutant and in the mips1 oxt6 CPSF30 complemented line.…”

“…These two proteins constitute a regulatory hub for genemediated and basal resistance and are required for the accumulation of SA, but several intermediates in this signaling cascade remain to be identified. We recently characterized the LMM mips1 mutant (also called Arabidopsis thaliana L-myo-Inositol-1-Phosphate Synthase1), which is deficient in D-MYOINOSITOL-3-PHOSPHATE SYN-THASE (MIPS), the key enzyme catalyzing the limiting step of myoinositol (MI) synthesis, using Glc-6-P as a substrate (Meng et al, 2009;Donahue et al, 2010;Luo et al, 2011). The Arabidopsis genome contains three genes encoding MIPS isoforms that share 89% to 93% identity at the amino acid level (GhoshDastidar et al, 2006;Torabinejad and Gillaspy, 2006), but MIPS1 appears to be responsible for most of the MI biosynthesis in leaves.…”

Phospholipid biosynthesis increases in RHD3-defective mutants

“…16 Interestingly, PIS overexpression rescued the phenotype of the MIPS mutants, and PIS2 was more efficient than PIS1 in such process. 17 Therefore, PIS1 appears to be engaged in the biosynthesis of the bulk of PI for membranes and its overexpression induces the biosynthesis of other phospholipids; on the other hand, PIS2 is more engaged in the biosynthesis of PI species for the production of phosphoinositides which are involved in the regulation of the secretory pathway. As a consequence, we wondered whether PIS1 but not PIS2 could be linked to some extent to RHD3 as it was described for Rab10 and PI metabolism in animal cells.…”

Comparative Expression and Cellular Localization of Myo-inositol Phosphate Synthase (MIPS) in the Wild Type and in an EMS Mutant During Common Bean (Phaseolus vulgaris L.) Seed Development

“…Myoinositol is the most important and abundant stereoisomer of the six-carbon cyclitol inosito (Luo et al 2011) and acts as a substrate for the formation of various inositol-derived molecules involved in many different and critical plant biochemical and physiological pathways, such as intracellular signal transduction (Stevenson-Paulik et al 2005), membrane construction and trafficking (Cullen et al 2001), and regulation of cell death (Donahue et al 2010). More recently, myo-inositol was reported to be the main substrate for synthesizing membrane phosphatidylinositol and phosphatidylinositides, which are essential for endomembrane structure and trafficking and thus for auxin-regulated embryogenesis (Luo et al 2011). The regulation, purification, characterization and localization of MIPS enzymes have been investigated by several authors (Abreau and Aragao 2007;Chiera and Grabau 2007;Mitsuhashi et al 2008).…”