Genomics and Genetic Engineering to Develop Metal/Metalloid Stress-Tolerant Rice

Abstract

Rapid industrialization and urbanization gradually shrink the cultivable land worldwide. To meet the growing demand for food, excessive application of fertilizer/pesticide and irrigation with sewage/industry effluent result in contamination of arable land with heavy metals. Rice, a major staple food used worldwide specially in the Asian countries, is also affected by heavy metal (HM) toxicity. These HMs affect plant growth and metabolism negatively and decrease crop quality and productivity. They are also able to enter the food chain and affect human health. Lead (Pb), zinc (Zn), copper (Cu), nickel (Ni), cadmium (Cd), chromium (Cr), mercury (Hg), arsenic (As), and antimony (Sb) are some of the metals and metalloids found in contaminated soil. Both the essential and nonessential elements are taken up by the plants through different metal transporters. As more HMs are being transported into the plants, deficiencies of essential elements and oxidative stress may occur. As a defense mechanism, plants employ different strategies to mitigate the oxidative stress. Genetically engineered plants are developed in such a way that they are equipped with the production of enhanced stress tolerance protein/metal sequestration mechanism/efficient metal efflux system/modified metal transporters, which can make them more adaptable in HM stress condition. Cultivation of tolerant/genetically engineered genotypes can help to eliminate metal toxicity and accumulation in grains. Rice grown in As/Cd-contaminated sites causes accumulation of these metals in grains, which is deleterious for health. Transgenic rice engineered with As(III)-S-adenosyl methyl transferase (arsM) decreased As accumulation in rice grains, and by gene manipulation, Cd entry in rice grain can also be blocked.