*2.5. Secondary Metabolites*

Broccoli contains a number of beneficial secondary metabolites, including glucosinolates/sulforaphane, carotenoids, phenolic acids and flavonoids. Several loci/genes regulating the accumulation of these compounds in broccoli have been identified. Genetic models of secondary metabolite biosynthesis in *Arabidopsis* provide a convenient tool for homologous studies in broccoli [108,109]. Via a homologous cloning strategy, some broccoli genes are isolated directly, including *cytochrome P450 79F1* (*CYP79F1*), *cytochrome P450 83A1* (*CYP83A1*), *UDP-glucosyltransferase 74B1* (*UGT74B1*), *sulfotransferase 18* (*ST5b*) and flavincontaining monooxygenase *GS-OX1* (*FMOGS-OX1*), *cytochrome P45083B1* (*BoCYP83B1*), *BoMYB51*, *GSL-PRO*, *GSL-ELONG*, *GSL-ALK*, *GSL-OH*, *Myb28* and *BoMYB51* for glucosinolate biosynthesis [109–113], and *BoPAL*, *BoDFR*, *BoTT8* and *BoTTG1* for anthocyanin biosynthesis [114]. Genetic loci determining the variation in these secondary metabolites were also detected by genetic mapping. Sotelo et al. performed genetic analysis to identify the genome regions regulating glucosinolate biosynthesis in the DH mapping population BolTBDH and detected eighty-two significant QTLs for individual and total glucosinolate synthesis in leaves, seeds and flower buds, and *QTL9.2* (proposed candidate as *GSL-ALK*) plays a central role in determining glucosinolate variation, showing epistatic interactions with other loci [115]. Brown et al. constructed a genetic linkage map with a broccoli mapping population, identified 14 QTLs associated with the accumulation of aliphatic, indolic or aromatic glucosinolates in florets, and a locus *GSL12* on C09 explains approximately 40% of the phenotypic variability of progoitrin [116]. Li et al. performed genetic mapping for sulforaphane metabolism with a DH population; 18 QTLs for sulforaphane metabolism in broccoli florets were identified, and six QTLs among them were detected in more than one environment [117]. Using the same population previously reported [116], Brown et al. constructed a genetic linkage map with an SNP array and identified three QTLs for carotenoid variation in broccoli florets [118]. Gardner et al. performed QTL analysis saturated with SNP markers in an Illumina 60 K array for total phenolic concentration and its individual components in the population previously reported by Brown et al. [118] and obtained twenty-three loci identified in at least two analyses [119]. In the BolTBDH mapping population, 33 QTLs were identified controlling phenolic concentrations in leaves, flower buds and seeds [120]. In addition, transcriptome analyses were performed to identify differentially expressed genes related to glucosinolate metabolism in broccoli seeds, sprouts and byproducts [121–123].
