Abstract
Plant carotenoids have been implicated in preventing several age-related diseases, and they also provide vitamin A precursors; therefore, increasing the content of carotenoids in maize grains is of great interest. It is not well understood, however, how the carotenoid biosynthetic pathway is regulated. Fortunately, the maize germplasm exhibits a high degree of genetic diversity that can be exploited for this purpose. Here, the accumulation of carotenoids and the expression of genes from carotenoid metabolic and catabolic pathways were investigated in several maize landraces. The carotenoid content in grains varied from 10.03, in the white variety MC5, to 61.50 μg·g−1, in the yellow-to-orange variety MC3, and the major carotenoids detected were lutein and zeaxanthin. PSY1 (phythoene synthase) expression showed a positive correlation with the total carotenoid content. Additionally, the PSY1 and HYD3 (ferredoxin-dependent di-iron monooxygenase) expression levels were positively correlated with β-cryptoxanthin and zeaxanthin, while CYP97C (cytochrome P450-type monooxygenase) expression did not correlate with any of the carotenoids. In contrast, ZmCCD1 (carotenoid dioxygenase) was more highly expressed at the beginning of grain development, as well as in the white variety, and its expression was inversely correlated with the accumulation of several carotenoids, suggesting that CCD1 is also an important enzyme to be considered when attempting to improve the carotenoid content in maize. The MC27 and MC1 varieties showed the highest HYD3/CYP97C ratios, suggesting that they are promising candidates for increasing the zeaxanthin content; in contrast, MC14 and MC7 showed low HYD3/CYP97C, suggesting that they may be useful in biofortification efforts aimed at promoting the accumulation of provitamin A. The results of this study demonstrate the use of maize germplasm to provide insight into the regulation of genes involved in the carotenoid pathway, which would thus better enable us to select promising varieties for biofortification efforts.
Highlights
The grass family (Poaceae), including maize, wheat, rice, sorghum, and millet, contains the major staple crops
We evaluated the expression of PSY1 because it encodes the first enzyme in the carotenoid biosynthetic pathway, as well as the expression of HYD3 and CYP97C because they encode the last enzymes in the same pathway; HYD3 is the last enzyme in the β,β branch, and CYP97C is the last enzyme in the β,ε branch
Gene expression analyses showed that PSY1, CYP97C and HYD3 were more highly expressed at the end of grain development and were positively correlated with the total carotenoid content
Summary
The grass family (Poaceae), including maize, wheat, rice, sorghum, and millet, contains the major staple crops. Maize is one of the most important cereal crops worldwide, as evidenced by the multiple ways in which it is exploited. Maize provides food and feed and is a resource for many unique industrial and commercial products, ranging from textiles and oil to pharmaceutical products. Maize alone is responsible for providing 15% of the total protein and 20% of the total calories in the human diet [1]. In addition to its nutritional importance, maize represents one of the most important sources of carotenoids [2,3]. Carotenoids are a complex class of isoprenoid pigments, which provide nutritional and functional value as both provitamin A and non-provitamin A compounds, such as lutein and zeaxanthin
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