# Mining of Potential Gene Resources for Breeding Nutritionally Improved Maize
## 1 Introduction  
M maize (_Zea mays_ L.) is one of the main food crops in the world, which stands first among the grain crops in terms of yield production. In addition to being used as food for humans, maize can also be used as animal feed or as raw material for industrial manufacturing. Maize kernels provide many nutrients, including starch, oil and protein, and are rich in microelements, such as vitamins and minerals. The pericarp has fiber and minerals; the aleurone layer contains high levels of minerals and antioxidants; the endosperm contains starch, protein, vitamins and antioxidants; and the embryo is rich in lipids, minerals and some vitamins [1]. Understanding the distribution of various nutrients facilitates the application of appropriate methods to obtain desired components (Figure 1).  
In face of the ever-changing demand for maize in the new era, traditional breeding strategies have the challenge of meeting human beings' demands, from yield improvement to nutritional quality improvement. Compared with traditional breeding methods, molecular breeding significantly shortens the breeding process and has attracted more and more attention. Genome engineering technologies, including the CRISPR-Cas9 based genome editing and ectopic expression of functional genes driven by strong or tissue-specific promoters, have paved the way for molecular breeding [2; 3]. So far, maize has the largest number of transgenic events that have been commercialized [4], which reflects the fact that maize improvement has attracted considerable attention and that genome engineering is profoundly changing the past and future of maize. Homologous genes among different plant species are highly likely to have similar functions. Many genes in model plant species such as rice (_Oryza sativa_) and _Arabidopsis thaliana_ have been known to control specific traits. However, their homologs have not been identified or studied in maize. Therefore, delivering knowledge from model species to maize would be a rapid way to deliver maize nutrient improvement.  
In this review, we focus on increasing the content of resistant starch, maize oil, essential amino acids, vitamins, minerals of iron and zinc, which are essential nutrients for human health. We summarize 107 genes that have been reported to be related to the above nutrient contents from different plant species, including _A. thaliana_, rice, soybean and potato, tomato, etc.; the protein sequences of these were used as queries to blast a maize genome with blastP on the Gramene website ([[http://ensembl.gramene.org/Zea_mays/Info/Index](http://ensembl.gramene.org/Zea_mays/Info/Index)]([http://ensembl.gramene.org/Zea_mays/Info/Index](http://ensembl.gramene.org/Zea_mays/Info/Index)), accessed on 20 February 2022). All obtained sequences a with low \(E\)-value (<10\({}^{-12}\)) were selected for manual inspection. The Pfam domain searches ([[http://pfam.xfam.org/](http://pfam.xfam.org/)]([http://pfam.xfam.org/](http://pfam.xfam.org/)), accessed on 20 February 2022) were performed to confirm the candidate sequences as maize homologs. In addition, chromosomal mapping of these genes was carried out according to their positions on the chromosomes (Figure S1). Using available RNA_seq data, we analyzed the expression patterns of the 246 maize potential gene resources in maize early seeds, kernels and non-seed tissues. In addition, we also discuss the strategies of using these genes to obtain desired traits, providing a valuable candidate gene pool for nutrient improvement in maize.