Manipulating the Phytic Acid Content of Rice Grain Toward Improving Micronutrient Bioavailability

Ishara Perera,Naoki Hirotsu,Saman Seneweera

doi:10.1186/s12284-018-0200-y

Ishara Perera, Naoki Hirotsu + Show 1 more

Open Access

https://doi.org/10.1186/s12284-018-0200-y

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Journal: Rice	Publication Date: Jan 11, 2018
Citations: 95	License type: open-access

Affiliation: Toyo University, University of Southern Queensland

Abstract

Myo-inositol hexaphosphate, also known as phytic acid (PA), is the most abundant storage form of phosphorus in seeds. PA acts as a strong chelator of metal cations to form phytate and is considered an anti-nutrient as it reduces the bioavailability of important micronutrients. Although the major nutrient source for more than one-half of the global population, rice is a poor source of essential micronutrients. Therefore, biofortification and reducing the PA content of rice have arisen as new strategies for increasing micronutrient bioavailability in rice. Furthermore, global climate change effects, particularly rising atmospheric carbon dioxide concentration, are expected to increase the PA content and reduce the concentrations of most of the essential micronutrients in rice grain. Several genes involved in PA biosynthesis have been identified and characterized in rice. Proper understanding of the genes related to PA accumulation during seed development and creating the means to suppress the expression of these genes should provide a foundation for manipulating the PA content in rice grain. Low-PA rice mutants have been developed that have a significantly lower grain PA content, but these mutants also had reduced yields and poor agronomic performance, traits that challenge their effective use in breeding programs. Nevertheless, transgenic technology has been effective in developing low-PA rice without hampering plant growth or seed development. Moreover, manipulating the micronutrient distribution in rice grain, enhancing micronutrient levels and reducing the PA content in endosperm are possible strategies for increasing mineral bioavailability. Therefore, a holistic breeding approach is essential for developing successful low-PA rice lines. In this review, we focus on the key determinants for PA concentration in rice grain and discuss the possible molecular methods and approaches for manipulating the PA content to increase micronutrient bioavailability.

Highlights

Myo-inositol 1,2,3,4,5,6-hexakisphosphate (InsP6), commonly known as phytic acid (PA) is the principle storage form of phosphorus (P) in cereal grains, and may account for 65%–85% of the total seed P (Raboy 2000)
In transgenic rice, reducing the PA content in seeds by suppressing RINO1 gene expression driven by the RINO1 or CaMV35S promoters resulted in an increase in available Inorganic Phosphate (Pi) but no reduction in the total seed P levels (Feng and Yoshida 2004)
Using these molecular techniques in future rice breeding should be an effective approach for reducing micronutrient deficiency issues; limited molecular level research studies have been carried out, and only a few Quantitative Trait Loci (QTLs) for PA content are known in rice

Summary

Background

Myo-inositol 1,2,3,4,5,6-hexakisphosphate (InsP6), commonly known as phytic acid (PA) is the principle storage form of phosphorus (P) in cereal grains, and may account for 65%–85% of the total seed P (Raboy 2000). In transgenic rice, reducing the PA content in seeds by suppressing RINO1 gene expression driven by the RINO1 or CaMV35S promoters resulted in an increase in available Pi but no reduction in the total seed P levels (Feng and Yoshida 2004) These investigators observed that the RINO1 and CaMV35S promoters were active in vegetative tissues in addition to developing seeds; the effects of the transgenes were low compared to the effects of the lpa mutants. Use of DNA Marker Technology Genetic DNA marker technology enhances the efficiency of plant breeding through marker-assisted selection of improved traits Using these molecular techniques in future rice breeding should be an effective approach for reducing micronutrient deficiency issues; limited molecular level research studies have been carried out, and only a few Quantitative Trait Loci (QTLs) for PA content are known in rice. Searching for low-PA/high micronutrient cultivars from diverse rice germplasm could be a beneficial approach for finding a donor cultivar that can be used in genetic approaches to enhance grain micronutrient content as a strategy for improving the nutritional value of human diets

Conclusions

Findings

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