# Mining of Potential Gene Resources for Breeding Nutritionally Improved Maize
## 5 Identification of Maize Potential Gene Resources for Vitamin Content Improvement  
After decades of relentless efforts by plant breeders, the yield of staple crops has increased dozens of times. However, hidden hunger, which refers to eating food that is insufficient in vitamins and micronutrients, becomes a new problem that afflicts more than 2 billion people globally. Crops such as corn are unable to provide sufficient micronutrients and need to undergo biofortification, which uses agricultural methodologies to augment \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Genes** & **Protein Function** & **Maize Orthology** & **Gene ID** & **Strategy** & **References** \\ \hline _AK_ & aspartate kinase & _ASK1_ & _Zm00001 eb064530_ & knockout & [52] \\ \hline _SYNC1_ & asparaginyl-tRNA synthetase & & _Zm00001 eb341390_ & overexpression & [53] \\ \hline _VSP_ & storage protein & _VSP1_ & _Zm00001 eb283460_ & overexpression & [54; 55] \\ \hline _BIP_ & storage protein & _BIP1_ & _Zm00001 eb229930_ & overexpression & [56] \\ \hline _CGS_ & cystathionine \(\gamma\)-synthase & _CGS1_ & _Zm00001 eb392050_ & overexpression & [57; 58] \\ \hline _TS1_ & threonine synthase & _THR1_ & _Zm00001 eb294790_ & & \\  & & _THR2_ & _Zm00001 eb284240_ & knockout & [60; 61] \\  & & _THR3_ & _Zm00001 eb022690_ & & \\  & & _Zm00001 eb088230_ & & & \\ \hline _HMT_ & homocysteine & _HMT1_ & _Zm00001 eb399940_ & overexpression & [67] \\ \hline _ASA_ & anthranilate synthase & & _Zm00001 eb063220_ & overexpression & [68; 69] \\ \hline _AAT_ & aspartate aminotransferase & _GOT1_ & _Zm00001 eb152450_ & & \\  & & _GOT2_ & _Zm00001 eb257910_ & overexpression & [63] \\  & & _GOT3_ & _Zm00001 eb238900_ & overexpression & [70] \\  & & _GOT4_ & _Zm00001 eb146400_ & & \\ \hline _ASNI_ & asparagine synthetase & _ASN3_ & _Zm00001 eb013430_ & overexpression & [70] \\  & & _ASN4_ & _Zm00001 eb396990_ & overexpression & [64] \\ \hline _SUT1_ & carrier protein & _SUT1_ & _Zm00001 eb005460_ & overexpression & [65] \\ \hline _AAP6_ & carrier protein & _AAAP21_ & _Zm00001 eb145670_ & overexpression & [65] \\ \hline _NAC100_ & transcription factor & _NACT32_ & _Zm00001 eb080700_ & knockout & [66] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: List of potential gene resources for elevating essential amino acid content in maize. the nutritional quality of food and counter micronutrient malnutrition [71]. Vitamins are essential micronutrients for growth, metabolism, reproduction and other processes related to human health. Vitamins can be classified into two groups: fat-soluble (A, D, E and K) and water-soluble (B and C). \(\beta\)-carotene is a kind of red-orange pigment, which imparts color and antioxidant properties to plants and fruits. When it enters the body, it turns into vitamin A. Deficiency in vitamin A can cause night blindness. Isoprenoids produced by the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway are carotenoid precursors [72]. 1-deoxy-D-xylulose 5-phosphate synthase (DXS) and 1-Deoxy-D-xylulose 5-phosphate reductio isomerase (DXR) are important catalytic enzymes for \(\beta\)-carotene synthesis. Phytoene desaturase (PDS) also promotes the formation of caroten. In addition to improving the synthesis efficiency through overexpressing key enzymes, some other factors that are not directly involved in the biosynthetic pathway have been shown to affect carotenoid accumulation in several plant species. Ectopic expression of ORANGE (OR), a plastidial DnaJ cysteine-rich domain-containing protein governing chromoplast biogenesis and carotenoid accumulation, promotes carotenoid accumulation and fruit development in tomatoes [73; 74]. Suppression of de-etiolated 1 (detI) that affects plant light absorption via RNAi alters the carotenoid content in tomatoes and _brassica napus_[75; 76]. Ectopic expression of a brassinazole-resistant 1 (bzr1-1d) transcription factor in brassinaored signaling enhances carotenoid accumulation in tomatoes [77].