###### Abstract  
Supplementation using selenium (Se) on plants is an effective and widely used approach. It can not only be converted to more Se rich compounds but promote the accumulation of glucosinolates (GSLs) with anti-carcinogenic properties. However, the molecular mechanism of Se in regulating GSLs synthesis remains unclear. In the present study, we analyzed the effects of Se treatment (50 uM sodium selenite) on GSLs, glucoraphanin (4 MSOB), and sulforaphanne compounds in brocoli tissues. The transcript levels of genes involved in sulfur absorption and transport, GSLs biosynthesis, translocation, and degradation pathways were also evaluated. The study showed that Se treatment remarkably promoted the accumulation of total sulfur and total Se contents and increased Trp-derived GSLs levels in roots by 2 times. The 4 MSOB concentration and sulforaphanne content in fresh leaves was increased by 67% and 30% after Se treatment, respectively. For genes expressions, some genes involved in sulfate uptake and transporters, GSLs biosynthesis, and transporters were induced strongly upon Se exposure. Results revealed that exogenous Se treatment promotes the overaccumulation of GSLs and 4 MSOB content in brocoli by activating the transcript levels of genes involved in sulfur absorption, GSLs biosynthesis, and translocation pathways. selenium application; _Brassica oleracan_ var. _italica_ Plenck; sulfur-rich metabolites; genes expression Received: 2 April 2022  
Accepted: 14 April 2022  
Published: 19 April 2022  
**Published: 19 April 2022**  
and pathogen invasion [8]. Concerning biosynthesis, the groups not only have different amino acid precursors but also differ in the actual biosynthetic enzymes and their regulation [4; 9; 10] (Figure S1). Hence, in physiological studies including this, the two groups are generally discussed separately. Some transcription factors, including _MYB28_, _MYB29_, and _MYB76_, are involved in regulating Met-derived GSLs biosynthesis [11; 12]. Other transcription factors, such as _MYB34_, _MYB51_, and _MYB122_ genes, are responsible for accumulating Trp-derived GSLs [13]. As specialized metabolites, GSLs contents and degradation products are susceptible to external stimuli [14; 15; 16]. Among them, supplementation using inorganic Se on broccoli is considered to be an effective and widely used approach because it can not only affect GSLs accumulation but produce more Se-rich compounds with anti-carcinogenic properties [17; 18]. Se is an essential micronutrient for many living organisms, which plays a crucial role in enhancing human immunity, reducing cancer risks, mitigating heavy metals toxicity, and alleviating abiotic stress [19; 20; 21; 22]. The Recommended Dietary Allowance (RDA) of Se consumption for adult males and females is 55-75 \(\upmu\)g/day. When the daily consumed level is low, 40 \(\upmu\)g or over 400 \(\upmu\)g, people will be suffered from corresponding dietary deficiency and toxicity symptoms, respectively [23]. Se uptake in humans primarily depends on the ingestion of Se-enriched fruits, vegetables, and crops [24; 25]. Se biofortification at an appropriate concentration on plants is an effective and convenient strategy for producing more Se-containing edible foods [26; 27]. Besides, Se supplementation can boost the accumulation of plants' secondary metabolites with benefits for human health [28], such as capsaicin in peppers [29],tocopherol and total phenols in mustards [30], phenolic acids and anthocyanins in lettuce [31], flavonoids and chalcone in tomatoes [32]. Se biofertilization on plants may also affect the production of GLSs, a class of sulfur-containing specialized metabolites [33; 34; 35]. Due to the similarities in chemical properties and physical structures between Se and sulfur, Se competes with the same sulfate transporters (SULTRs) and sulfur assimilation genes with sulfur in plants [36; 37]. Previous studies have concluded that Se application leads to a reduction in GSLs contents, especially Met-derived GSLs, including ITCs and sulforaphane levels [38].