Abstract
BackgroundPhytic acid (InsP6) is considered as the major source of phosphorus and inositol phosphates in cereal grains. Reduction of phytic acid level in cereal grains is desirable in view of its antinutrient properties to maximize mineral bioavailability and minimize the load of phosphorus waste management. We report here RNAi mediated seed-specific silencing of myo-inositol-3-phosphate synthase (MIPS) gene catalyzing the first step of phytic acid biosynthesis in rice. Moreover, we also studied the possible implications of MIPS silencing on myo-inositol and related metabolism, since, first step of phytic acid biosynthesis is also the rate limiting step of myo-inositol synthesis, catalyzed by MIPS.ResultsThe resulting transgenic rice plants (T3) showed a 4.59 fold down regulation in MIPS gene expression, which corresponds to a significant decrease in phytate levels and a simultaneous increment in the amount of inorganic phosphate in the seeds. A diminution in the myo-inositol content of transgenic plants was also observed due to disruption of the first step of phytic acid biosynthetic pathway, which further reduced the level of ascorbate and altered abscisic acid (ABA) sensitivity of the transgenic plants. In addition, our results shows that in the transgenic plants, the lower phytate levels has led to an increment of divalent cations, of which a 1.6 fold increase in the iron concentration in milled rice seeds was noteworthy. This increase could be attributed to reduced chelation of divalent metal (iron) cations, which may correlate to higher iron bioavailability in the endosperm of rice grains.ConclusionThe present study evidently suggests that seed-specific silencing of MIPS in transgenic rice plants can yield substantial reduction in levels of phytic acid along with an increase in inorganic phosphate content. However, it was also demonstrated that the low phytate seeds had an undesirable diminution in levels of myo-inositol and ascorbate, which probably led to sensitiveness of seeds to abscisic acid during germination. Therefore, it is suggested that though MIPS is the prime target for generation of low phytate transgenic plants, down-regulation of MIPS can have detrimental effect on myo-inositol synthesis and related pathways which are involved in key plant metabolism.Electronic supplementary materialThe online version of this article (doi:10.1186/1939-8433-6-12) contains supplementary material, which is available to authorized users.
Highlights
Phytic acid (InsP6) is considered as the major source of phosphorus and inositol phosphates in cereal grains
In the present study we report RNA interference (RNAi) mediated silencing of myo-inositol −3- phosphate synthase (MIPS) gene, catalyzing the first step of phytic acid biosynthesis in indica rice cultivar
PCR amplification of genomic DNA from 21 day old plants resulted in amplification of wheat RGA2 intron only in transgenic positive plants while no amplification was observed in non-transgenic control plants (Figure 1b)
Summary
Phytic acid (InsP6) is considered as the major source of phosphorus and inositol phosphates in cereal grains. We report here RNAi mediated seed-specific silencing of myo-inositol-3-phosphate synthase (MIPS) gene catalyzing the first step of phytic acid biosynthesis in rice. Phytic acid (InsP6) is considered as the major source of phosphorus and inositol phosphates. Degradation of phytate mediated by the action of phytase, releases the bound mineral cations, phosphorus and myo-inositol which are required for proper growth and development of seedlings (Raboy 2002). The monogastric animals, due to lack of this phytase enzyme, cannot digest phytate efficiently, rendering the bound phosphorus and mineral cations (Fe2+, Zn2+, Ca2+) unavailable for absorption (Bregitzer and Raboy 2006). Various attempts have been made to develop low phytate crops which would facilitate improvement in the bioavailability of phosphorus and micronutrients
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