## 3 Flavonoids
### Biosynthesis of Flavonoids
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Genes** & **Enzyme and Its Alternative Names in** & **Functions** \\  & **Arabidopsis** & **Functions** \\ \hline _At2g37040_ & PAL, phenylalanine ammonia lyase & The deamination of phenylalanine to trans-cinnamic acid [178; 179] \\ \hline _At3g53260_ & PAL, phenylalanine ammonia lyase & The hydroxylation of trans-cinnamic acid [180; 181] \\ \hline _At2g30490_ & C4H, Cinnamic acid 4-hydroxylase & The hydroxylation of trans-cinnamic acid [180; 181] \\ \hline _At1g65060_ & 4 CL, 4-comarate CoA ligase & Coumaric acid conversion to coumaroyl-CoA, which is the last step of phenylpropanoid pathway [182] \\ \hline _At5g13930_ & CHS, chalcone synthase (ATCHS, Transparent Testa 4, TT4) & The condensation of activated coumaric acid with three molecules of activated malonic acid in the form of malonyl-CoA to the formation of naringenin-chalcone. A key enzyme involved in the biosynthesis of flavonoids [183] \\ \hline _At3g55120_ & CHI, chalcone isomerase (A11, ATCHI, Chalcone flavanone isomerase, Transparent Testa 5, TT5) & Catalysis of the conversion of chalcone into flavanones [183]. _At3g55120_ is co-expressed with CHS encoding gene [60] \\ \hline _At3g51240_ & F3H, flavanone 3-hydroxylase & Encodes flavanone 3-hydroxylase that is coordinately expressed with CHSs and CHIs and involved in flavonoid biosynthesis [184] \\ \hline _At5g07990_ & F3H, flavanone 3\({}^{\prime}\)-hydroxylase (CYP75B1, Cytochrome P450 75B1, D501, Transparent Testa 7, TT7) & Hydroxylation of 3\({}^{\prime}\)-position of B-ring of flavonoids with catalysis of dihydroquercetin and quercetin formation from dihydrokaempferol and kaempferol, respectively [184] \\ \hline _At5g24530_ & FNS, flavone synthase (AtDMR6, Downy Mildew Resistant6) & The conversion of the flavanones into flavones. This class is also shown to comprise soluble Fe\({}^{2+}\)/2-oxoglutate-dependent dioxygenases, which are oxygen- and NADPH-dependent cytochrome P450 membrane-bound monooxygenases [185] \\ \hline _At5g08640_ & \begin{tabular}{c} Encodes a flavonol synthase that catalyzes formation of flavonols from dihydroflavonols. Co-expressed with CHI and CHS (qRT-PCR) \\ \end{tabular} & \begin{tabular}{c} Encodes a flavonol synthase that catalyzes formation of flavonols from dihydroflavonols. Co-expressed with CHI and CHS (qRT-PCR) \\ \end{tabular} \\ \hline _At5g63590_ & \begin{tabular}{c} The reduction of the 4-keto group of dihydroflavonol to the corresponding leucoanthocyanidin. Synthesis of phlobahenes from flavan-4-oles in _Zea mays_[186] \\ \end{tabular} \\ \hline _At5g42800_ & DFR, dihydroflavonol 4-reductase & \begin{tabular}{c} The reduction of the 4-keto group of dihydroflavonol to the corresponding leucoanthocyanidin. Synthesis of phlobahenes from flavan-4-oles in _Zea mays_[186] \\ \end{tabular} \\ \hline _At1g61720_ & ANR, anthocyanin reductase & \begin{tabular}{c} Synthesis of proanthocyanidin (condensed tannins) from leukoanthocyanidins and anthocyanin [13] \\ \end{tabular} \\ \hline _At4g22880_ & \begin{tabular}{c} ANS, anthocyanin synthase (LDOX, Leucanthocyanidin dioxygenase) \\ \end{tabular} & Convertion leucoanthocyanidins to anthocyanins [187] \\ \hline _At5g17050_ & \begin{tabular}{c} \\ _At1g30530_ \\ \end{tabular} & \begin{tabular}{c} FGT, flavonoid glycosyltransferases \\ \end{tabular} & Glycosylation of anthocyanins to anthocyanins [188; 189; 190; 191] \\ \hline _At2g36790_ & \begin{tabular}{c} FGT, flavonoid glycosyltransferases \\ \end{tabular} & Glycosylation of anthocyanins to anthocyanins [188; 189; 191] \\ \hline _At1g60600_ & \begin{tabular}{c} \\ _At4g14090_ \\ \end{tabular} & \begin{tabular}{c} \\ _At5g54060_ \\ \end{tabular} & \
\begin{tabular}{c} MYB domain protein 12, MYB12, \\ ATMYB12, PFG1 \\ \end{tabular} & Flavonol synthesis regulators. Strongly activate the promoters of CHS, F3H, FLS, and CHI [192] \\ \hline _At5g49330_ & AtMYB111, PFG3 &
\begin{tabular}{c} FIA7 (ABA-inducible bHLH-type \\ transcription factor), AIB, ATAIB, \\ JA-associated MYC2-like 1, JAM1 \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}