Genetic and physiological analysis of iron biofortification in maize kernels

Background

Maize is a major cereal crop widely consumed in developing countries, which have a high prevalence of iron (Fe) deficiency anemia. The major cause of Fe deficiency in these countries is inadequate intake of bioavailable Fe, where poverty is a major factor. Therefore, biofortification of maize by increasing Fe concentration and or bioavailability has great potential to alleviate this deficiency. Maize is also a model system for genomic research and thus allows the opportunity for gene discovery. Here we describe an integrated genetic and physiological analysis of Fe nutrition in maize kernels, to identify loci that influence grain Fe concentration and bioavailability.

Methodology

Quantitative trait locus (QTL) analysis was used to dissect grain Fe concentration (FeGC) and Fe bioavailability (FeGB) from the Intermated B73 × Mo17 (IBM) recombinant inbred (RI) population. FeGC was determined by ion coupled argon plasma emission spectroscopy (ICP). FeGB was determined by an in vitro digestion/Caco-2 cell line bioassay.

Conclusions

Three modest QTL for FeGC were detected, in spite of high heritability. This suggests that FeGC is controlled by many small QTL, which may make it a challenging trait to improve by marker assisted breeding. Ten QTL for FeGB were identified and explained 54% of the variance observed in samples from a single year/location. Three of the largest FeGB QTL were isolated in sister derived lines and their effect was observed in three subsequent seasons in New York. Single season evaluations were also made at six other sites around North America, suggesting the enhancement of FeGB was not specific to our farm site. FeGB was not correlated with FeGC or phytic acid, suggesting that novel regulators of Fe nutrition are responsible for the differences observed. Our results indicate that iron biofortification of maize grain is achievable using specialized phenotyping tools and conventional plant breeding techniques.

Why nutritional iron deficiency persists as a worldwide problem

The earliest studies of food iron absorption employing biosynthetically incorporated radioisotopes were published in the 1950s. Wheat flour has been fortified with iron in Canada, the United Kingdom, and the United States since the 1940s. However, half a century later, nutritional iron deficiency (ID) is estimated to affect 1.5-2 billion people worldwide. The reasons for the apparently limited impact of health and nutrition policies aimed at reducing the prevalence of ID in developing countries are complex. They include uncertainty about the actual prevalence of ID, particularly in regions where malaria and other infections are endemic, failure of policy makers to recognize the relationships between ID and both impaired productivity and increased morbidity, concerns about safety and the risks to iron-sufficient individuals if mass fortification is introduced, and technical obstacles that make it difficult to add bioavailable iron to the diets of those at greatest risk. It is, however, likely that the next decade will see a marked reduction in the prevalence of ID worldwide. More specific assessment tools are being standardized and applied to population surveys. The importance of preventing ID during critical periods of the life cycle is receiving increased attention. Innovative approaches to the delivery of bioavailable iron have been shown to be efficacious. The importance of integrating strategies to improve iron nutrition with other health measures, and economic and social policies addressing poverty as well as trade and agriculture, are receiving increasing consideration.

Select what you need: a comparative evaluation of the advantages and limitations of frequently used expression systems for foreign genes

The expression of heterologous proteins in microorganisms using genetic recombination is still the high point in the development and exploitation of modern biotechnology. People can produce bioactive proteins from relatively cheap culture medium instead of expensive extraction. Host cell systems for the expression of heterologous genes are generally prokaryotic or eukaryotic systems, both of which have inherent advantages and drawbacks. An optimal expression system can be selected only if the productivity, bioactivity, purpose, and physicochemical characteristics of the interest protein are taken into consideration, together with the cost, convenience and safety of the system itself. Here, we concisely review the most frequently used prokaryotic, yeast, insect and mammalian expression systems, as well as expression in eukaryote individuals. The merits and demerits of these systems are discussed.