The Silencing of Carotenoid β-Hydroxylases by RNA Interference in Different Maize Genetic Backgrounds Increases the β-Carotene Content of the Endosperm

Abstract

Maize (<i>Zea mays</i> L.) is a staple food in many parts of Africa, but the endosperm generally contains low levels of the pro-vitamin A carotenoid β-carotene, leading to vitamin A deficiency disease in populations relying on cereal-based diets. However, maize endosperm does accumulate high levels of other carotenoids, including zeaxanthin, which is derived from β-carotene via two hydroxylation reactions. Blocking these reactions could therefore improve the endosperm β-carotene content. Accordingly, we used RNA interference (RNAi) to silence the endogenous <i>ZmBCH1</i> and <i>ZmBCH2</i> genes, which encode two non-heme di-iron carotenoid β-hydroxylases. The genes were silenced in a range of maize genetic backgrounds by introgressing the RNAi cassette, allowing us to determine the impact of <i>ZmBCH1</i>/<i>ZmBCH2</i> silencing in diverse hybrids. The β-carotene content of the endosperm increased substantially in all hybrids in which <i>ZmBCH2</i> was silenced, regardless of whether or not <i>ZmBCH1</i> was silenced simultaneously. However, the β-carotene content did not change significantly in C17 hybrids (M7 × C17 and M13 × C17) compared to C17 alone, because <i>ZmBCH2</i> is already expressed at negligible levels in the C17 parent. Our data indicate that <i>ZmBCH2</i> is primarily responsible for the conversion of β-carotene to zeaxanthin in maize endosperm.