Rice Carotenoid Biofortification and Yield Improvement Conferred by Endosperm-specific Overexpression of

Carotenoids, indispensable isoprenoid phytonutrients, are synthesized in plastids and are known to be deficient in rice endosperm. Many studies, involving transgenic manipulations of carotenoid biosynthetic genes, have been performed to obtain carotenoid-enriched rice grains. Nuclear-encoded GOLDEN2-LIKE (GLK) transcription factors play important roles in the regulation of plastid and thylakoid grana development. Here, we show that endosperm-specific overexpression of rice gene () leads to enhanced carotenoid production, increased grain yield, but deteriorated grain quality in rice. Subsequently, we performed the bioengineering of carotenoids biosynthesis in rice endosperm by introducing other three carotenogenic genes, , , and , which encode the enzymes truncated 3-hydroxy-3-methylglutaryl-CoA reductase, phytoene synthase, and phytoene desaturase, respectively. Transgenic overexpression of all four genes (, , , and ) driven by rice endosperm-specific promoter established a mini carotenoid biosynthetic pathway in the endosperm and exerted a roughly multiplicative effect on the carotenoid accumulation as compared with the overexpression of only three genes (, , and ). In addition, the yield enhancement and quality reduction traits were also present in the transgenic rice overexpressing the selected four genes. Our results revealed that confers favorable characters in rice endosperm and could help to refine strategies for the carotenoid and other plastid-synthesized micronutrient fortification in bioengineered plants.