Rice biofortification: breeding and genomic approaches for genetic enhancement of grain zinc and iron contents

Abstract

Rice is a highly consumed staple cereal cultivated predominantly in Asian countries, which share 90% of global rice production. Rice is a primary calorie provider for more than 3.5 billion people across the world. Preference and consumption of polished rice have increased manifold, which resulted in the loss of inherent nutrition. The prevalence of micronutrient deficiencies (Zn and Fe) are major human health challenges in the 21^st century. Biofortification of staples is a sustainable approach to alleviating malnutrition. Globally, significant progress has been made in rice for enhancing grain Zn, Fe, and protein. To date, 37 biofortified Fe, Zn, Protein and Provitamin A rich rice varieties are available for commercial cultivation (16 from India and 21 from the rest of the world; Fe > 10 mg/kg, Zn > 24 mg/kg, protein > 10% in polished rice as India target while Zn > 28 mg/kg in polished rice as international target). However, understanding the micronutrient genetics, mechanisms of uptake, translocation, and bioavailability are the prime areas that need to be strengthened. The successful development of these lines through integrated-genomic technologies can accelerate deployment and scaling in future breeding programs to address the key challenges of malnutrition and hidden hunger.

Keywords: biofortification; breeding; genomics; iron; rice; zinc.

Figure 1

Biofortification priority index (BPI) global rankings and priority levels for rice-consuming countries in Asia, Africa, and Latin America and the Caribbean (LAC).

Figure 2

Soil strategies of micronutrient availability in crops. (A) Zn and Fe dynamics in soil. (B) Zn and Fe translocation from soil to plant. OsYSL15, an iron-regulated iron (III)-deoxymugineic acid transporter; OsTOM1, TRANSPORTER OF MUGINEIC ACID 1; IRT-1, Iron-Regulated Transporter 1; ZIP1, ZRT, IRT-like protein; FRO2 gene, Ferric Chelate Reductase gene; AHA2, Arabidopsis plasma membrane H⁺-ATPase 2 gene; ABCG3, The ATP-binding cassette (ABC) transporter.

Figure 3

Percent distribution of iron (Fe) and zinc (Zn) in different parts of rice grain. Fe-PA, iron–phytic acid complex; Zn-PA, zinc–phytic acid complex.

Figure 4

Integrated breeding approaches for rice biofortification. AAS, atomic absorption spectroscopy; XRF/ED-XRF, energy-dispersive X-ray fluorescence; ICP-OES, inductively coupled plasma–optical emission spectroscopy; QTL, quantitative trait loci; GWAS, genome-wide association study; AICRIP, All India Coordinated Rice Improvement Programme; MLT, Multi Locational Trial; CRISPR/Cas9, Clustered Regularly Interspaced Short Palindromic Repeats, CRISPR-associated proteins9 technology; SSR, simple sequence repeats; SNP, single-nucleotide polymorphism; CAPS, cleaved amplified polymorphic sequences; MAS, marker-assisted selection; MABC, marker-assisted backcrossing; MARS, marker-assisted recurrent selection.