## 1 Introduction
They are divided into early biosynthetic genes (EBGs) and late biosynthetic genes (LBGs). EBGs include chalcone synthase, chalcone isomerase, flavonoid 3-hydroxy, flavonoid 3'-hydroxyase (F3'H), and flavonoid synthase. LBGs include dihydroflavonol 4-reductase (DFR), leucine anthocyanin oxygenase (LDOX), anthocyanin reductase, and UDP-glucose: flavonoid 3-O-glucoseyltransferase. Among these, \(F3^{\prime}H\) belongs to the CYP75B subfamily of the cytochrome P450-dependent monooxygenase (P450) superfamily. It converts dihydroflavanol into colorless cyanidin and is the key enzyme for the synthesis of cyanidin [32; 33]. [PERSON] et al. recently crossed the white radish inbred line YAAS-WR1 with the red radish inbred line YAAS-RR1. The genetic analyses highlighted \(R\)_Sr3'H_ and \(R\)_sMYB1.3_ as key candidates for controlling anthocyanin pigmentation in radish [34]. Green broccoli can sometimes produce light purple buds due to various environmental factors, significantly reducing its market value. The plant receptors detect the changes in environmental factors and activate a series of downstream transcription factors, which directly or indirectly regulate the expression of anthocyanin biosynthetic genes [35; 36]. In purple kale, the expression of \(DFR\) and \(LDOX\) genes in the anthocyanin synthesis pathway was induced under UV-A and UV-B treatments, increasing anthocyanin accumulation [37]. [PERSON] et al. found that \(BrMYB2\) and \(BrTT8\) might co-activate anthocyanin structural genes in purple-head Chinese cabbage after low-temperature induction, while the \(BrMYB2\) gene was downregulated and some negative regulators were upregulated in white-head cabbage [38]. Studies have shown that green leaves accumulated anthocyanins under low temperatures with excessive light exposure in maize, thereby shading chloroplasts and preventing the risk of photo-inhibition [39; 40]. The \(HY5\) transcription factor may be a central integrator of light and temperature signaling pathways in regulating anthocyanin biosynthesis in _Arabidopsis_[36]. Several previous studies have been performed on anthocyanins biosynthesis in broccoli. In purple broccoli, cyanidin was identified as a predominant anthocyanin isomer using HPLC-UV photo-diode array detection (PAD)-electrospray ionization (ESI)-MS/MS (HPLC-PAD-ESI-MS/MS) analysis [10; 41]. [PERSON] et al. used 127 doubled-haploid segregation populations of broccoli to construct a genetic map and localized a major locus and two minor loci on chromosome C1 controlling the purple sepal trait of flower heads at low temperatures [42]. [PERSON] et al. analyzed the dynamic transcript levels of structural and regulatory genes related to anthocyanin synthesis in purple broccoli with real-time quantitative analysis. They showed that the transcription factor _BoTT8_ was expressed in coordination with anthocyanin biosynthesis genes and activated their expression at the same time [43]. Fine localization and the candidate gene identification in purple cauliflower mutants also clearly revealed that the insertion of transposons upstream of the _BoMYB2_ promoter resulted in the activation of _BoMYB2_, which led to the ectopic accumulation of pigments in the mutants [27]. Molecular marker-assisted selection (MAS) plays an important role in modern plant breeding thanks to the aid of molecular markers closely linked to target genes. The genome-wide selection of single plants can be performed using MAS, which quickly recovers the genotype of the recurrent parent. As a general rule, two to four markers per 100 cM can be efficiently used to accelerate the recovery of the recipient parent in the early generations, such as BC1 or BC2 [44].