RNAi-Mediated Downregulation of Inositol Pentakisphosphate Kinase (IPK1) in Wheat Grains Decreases Phytic Acid Levels and Increases Fe and Zn Accumulation.

Sipla Aggarwal,Siddharth Tiwari,Gazaldeep Kaur,Vishnu Shukla,Anil Kumar,Ajay K Pandey,Kaushal K Bhati

doi:10.3389/fpls.2018.00259

Sipla Aggarwal, Siddharth Tiwari + Show 5 more

Open Access

https://doi.org/10.3389/fpls.2018.00259

Copy DOI

Abstract

Enhancement of micronutrient bioavailability is crucial to address the malnutrition in the developing countries. Various approaches employed to address the micronutrient bioavailability are showing promising signs, especially in cereal crops. Phytic acid (PA) is considered as a major antinutrient due to its ability to chelate important micronutrients and thereby restricting their bioavailability. Therefore, manipulating PA biosynthesis pathway has largely been explored to overcome the pleiotropic effect in different crop species. Recently, we reported that functional wheat inositol pentakisphosphate kinase (TaIPK1) is involved in PA biosynthesis, however, the functional roles of the IPK1 gene in wheat remains elusive. In this study, RNAi-mediated gene silencing was performed for IPK1 transcripts in hexaploid wheat. Four non-segregating RNAi lines of wheat were selected for detailed study (S3-D-6-1; S6-K-3-3; S6-K-6-10 and S16-D-9-5). Homozygous transgenic RNAi lines at T4 seeds with a decreased transcript of TaIPK1 showed 28–56% reduction of the PA. Silencing of IPK1 also resulted in increased free phosphate in mature grains. Although, no phenotypic changes in the spike was observed but, lowering of grain PA resulted in the reduced number of seeds per spikelet. The lowering of grain PA was also accompanied by a significant increase in iron (Fe) and zinc (Zn) content, thereby enhancing their molar ratios (Zn:PA and Fe:PA). Overall, this work suggests that IPK1 is a promising candidate for employing genome editing tools to address the mineral accumulation in wheat grains.

Highlights

Mineral malnutrition is among the most critical worldwide challenges to humankind
The expression validation for TaIPK1 homoeologs was performed in C306, an Indian hexaploid wheat variety. qRT-PCR showed high transcript level of TaIPK1-2B at different developmental stages (14 and 21 day after anthesis (DAA)) (Figure 1)
IPK1 had been a target of choice to achieve low phytate crops (Stevenson-Paulik et al, 2005; Shukla et al, 2009; Ali et al, 2013a)

Summary

Introduction

In developing countries ∼50% of the children are estimated to be micronutrient deficient (WHO, 2007). This condition might be a result of crop production in areas with low mineral phytoavailability and/or consumption of staple crops with inherently low tissue mineral concentrations (Welch and Graham, 2005). The mineral malnutrition can be addressed through dietary enhancement, mineral supplementation, food fortification, or increasing the concentrations and/or bioavailability of mineral elements. Methodologies to expand dietary enhancement, mineral supplementation, and food fortification have not generally been very effective (White and Broadley, 2005). Biofortification of crops by decreasing the concentration of antinutrients and other secondary metabolites can be considered as an important means to increase the bioavailability of mineral elements

Methods

Results

Conclusion