# Metabolism and Regulation of Ascorbic Acid in Fruits
## 4 Regulatory Genes That Control Ascorbic Acid Accumulation  
Aside from genetic engineering to control the expression of genes related to AsA metabolism, plants have a variety of transcriptional and translational regulatory mechanisms. The transcription factors can bind to gene promoters and control the expression of target genes at the transcriptional level. There have been some preliminary studies on the regulation of AsA accumulation in fruits by transcription factors (Table 3). _SIICE1_, a bHLH transcription factor, is closely related to chilling resistance in tomatoes. Overexpression of _SIICE1_ in tomatoes increases the AsA content in the ripe red fruit of tomato and improves the resistance of tomato fruit to low-temperature stress [105]. In tomato L1L4 transcription factor mutants, AsA content is significantly increased, suggesting that L1L4 may negatively influence AsA synthesis [106]. Heterologous expression of _Arabidopsis_ brassinosteroloid response transcription factor Brassinazole resistant 1 (_BZR1-1D_) in tomato can significantly increase AsA content in fruit [107]. It is found that MADS-box and CCAAT motifs are \begin{table}
\begin{tabular}{c c c c c c} \hline
**Common Name** & **Gene Name** & **Gene Source** & **Strategy** & **Change of AsA Content** & **Fold Change** & **Reference** \\ \hline tomato & GMP3 & tomato & overexpression & up & 1.1–1.6 & [85] \\ GMP3 & tomato & RNAi & down & 1.3–2.4 & [85] \\  & GME1 & tomato & overexpression & up & 1.6 & [86] \\  & GME1 & tomato & RNAi & no change & 0 & [87] \\  & GME2 & tomato & overexpression & up & 1.2 & [86] \\  & GME2 & tomato & RNAi & no change & 0 & [87] \\  & GME1 \(\times\) GME2 & tomato & RNAi & down & 0.2–0.6 & [38] \\  & GGP & tomato & overexpression & no change & 0 & [35] \\  & GGP & tomato & mutant & down & 0.5 & [88; 89] \\  & GGP & kiwifruit & overexpression & up & 2.0 & [90] \\  & GGP \(\times\) GPP & tomato & overexpression & no change & 0 & [35] \\  & SIMP3 & tomato & overexpression & up & 0.3–0.6 & [93] \\  & SIMP3 & tomato & antisense & down & 0.3–0.7 & [93] \\  & GLDH & tomato & RNAi & no change & 0 & [17] \\  & GLOase & rat & overexpression & up & 1.5 & [94] \\  & MIMO & _Arabidopsis_ & overexpression & up & 1.4 & [95] \\  & MIOX4 & tomato & overexpression & up & 1.5–2.3 & [96] \\  & GalUK & strawberry & overexpression & up & 1.2–2.5 & [97] \\  & AY & tomato & RNAi & up & 1.4–2.2 & [100] \\  & AO & tomato & RNAi & up & 0.3 & [101] \\  & DHAR1 & tomato & overexpression & up & 0.4 & [102] \\  & DHAR2 & tomato & overexpression & no change & 0 & [102] \\  & MDHAR & tomato & overexpression & up & 0.7 & [56] \\ \hline kiwifruit & GGP3 & kiwifruit & overexpression & up & 2.0–6.4 & [91; 92] \\ \hline strawberry & GGP & kiwifruit & overexpression & up & 2.0 & [90] \\ \hline \end{tabular}
\end{table} 
Table 2: Relationship between expression patterns of AsA metabolism-related genes and AsA accumulation in fruits. enriched in the promoters of tomato AsA synthesis-related genes, indicating that a single transcription factor may regulate multiple AsA synthesis genes [108]. Overexpression of the banana _MaMADS7_ transcription factor in tomatoes significantly increases the AsA content in the fruit [109]. The CCAAT-box transcription factor SINFYA10 in tomatoes can bind to the promoter of _SIGMET_1 and negatively regulate the expression of _SIGMET_1 and the level of AsA in leaves and fruits [110]. An HD-Zip I family transcription factor SIHZ24 is identified in tomato, which binds to the promoter of _SIGMP3_, activates the expression of _SIGMP3_, and then positively regulates the accumulation of AsA [111]. In addition, _SHZ24_ can bind to the promoters of _GME2_ and _GGP_ and regulate the accumulation of AsA by multiple targets [111]. _MdERF98_ activates the expression of _MdGMP1_, thereby promoting the synthesis of AsA in apple [36]. Transient expression of _AcERF91_ in kiwifruit can increase AsA content. At the same time, _AcERF91_ can bind to the promoter of _AcGGP3_ and activate the transcription of _AcGGP3_[112].