# Metabolism and Regulation of Ascorbic Acid in Fruits
## 4 Regulatory Genes That Control Ascorbic Acid Accumulation
Pattern regulation of the _AceMYBS1_ gene indicated that _AceMYBS1_ positively regulates AsA accumulation in kiwifruit [92]. In addition, AceMYBS1 can also bind to the _AceGGP3_ promoter and activate its expression, indicating that multiple transcription factors may simultaneously regulate the expression of a single AsA synthesis-related gene [92]. In addition, some transcription factors that regulate AsA degradation and regeneration are also identified. MdMYB1 can bind to the promoter of _MdDHAR_, activate the expression of _DHAR_, and then increase the content of AsA in apples [113]. MsSCL26.1 can bind to the P1 region of the _MsMDHAR_ promoter and activate the transcription of _MsMDHAR_, thereby inhibiting the synthesis of AsA in the apple [114]. After transient expression of _MYB_, _NAC_, and _ZIF_ transcription factors in tomato, AsA metabolism-related genes, such as _GMP2_, _GalUR_, _AO2_, and _APX6_, are significantly upregulated [115]. Transcript levels of _CaMYB16_ gene and _GLDH_ in pepper fruit are highly correlated, indicating that _CaMYB16_ may be involved in ascorbic acid synthesis in pepper fruit [116]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Common Name** & **Gene** & **Gene** & **Target Gene** & **Combination** & **Effect** & **Reference** \\ \hline tomato & ICE1 & tomato & not described & not & positively regulate the accumulation of AsA & [105] \\  & L114 & tomato & not described & described & Negatively regulate the accumulation of AsA & [106] \\  & BZR1-1D & _Arabidopsis_ & not described & not & positively regulate the accumulation of AsA & [107] \\  & MADS7 & banana & described & described & positively & \\  & NFYA10 & tomato & GME1 & protein-DNA & Negatively regulate the expression of GME1 and the accumulation of AsA. & [110] \\  & HZ24 & tomato & GMP3 & protein-DNA & Positively regulate the expression of GMP3 and the accumulation of AsA. & [111] \\  & HZ24 & tomato & GME2 & protein-DNA & Positively regulate the expression of GME2 and the accumulation of AsA. & [111] \\  & HZ24 & tomato & GGP & protein-DNA & Positively regulate the expression of GGP and the accumulation of AsA. & [111] \\ \hline apple & ERP98 & apple & GMP1 & protein-DNA & Positively regulate the expression of GMP1 and the accumulation of AsA. & [36] \\  & MYB1 & apple & DHAR & protein-DNA & Positively regulate the expression of DHAR and the accumulation of AsA. & [113] \\  & SCL26.1 & apple & MDHAR & protein-DNA & Positively regulate the expression of MDHAR and negatively regulate the accumulation of AsA. & [114] \\  & AMR1L1 & apple & GMP1 & protein-protein & Stimulate GMP1 degradation and negatively regulate the accumulation of AsA. & [36] \\  & mdm-m-mriR171i & apple & SCL26.1 & RNA-DNA & Stimulate SCL26.1 degradation and positively regulate the accumulation of AsA. & [114] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Regulation of AsA metabolism-related genes at the transcriptional and protein levels. The research on the regulatory mechanism of AsA accumulation at the protein level is still minimal (Table 3). AcSE3 and AcMYBR can interact with AcGGP3 to regulate AsA synthesis in kiwifruit [91]. As a result of _MdAMR1L1_ overexpression or silencing in apples, a negative relationship between Asc levels and _MdAMR1L1_ is detected [36]. MdAMR1L1 protein stimulated MdGMP1 degradation through ubiquitination, inhibiting AsA biosynthesis at a post-translational level [36]. In addition to the genes that can encode proteins, there are many noncoding RNAs in the plant genome. In plant development, the function of small ncRNAs, such as microRNAs and small interfering RNAs, has been extensively studied in the past decade. In total, 118 differentially expressed lncRNAs (DE-lncRNAs) and 32 differentially expressed microRNAs are identified during seabuckthorn fruit development [117]. These DE-lncRNAs are particularly enriched in the biosynthesis of AsA, carotenoids, and flavonoids.