Introduction
Sclerotiniasclerotiorumis a necrotrophic fungal pathogen that infects many of plants, such as rapeseed, soybean, dry pea, peanut, chickpea and sunflower and so on (Boland and Hall 1994; Bolton et al. 2010)[1-3](G., Mehta et al. 2008, Bolton, Thomma et al. 2010, Smolińska and Kowalska 2018). The fungus could cause stem rot in B. napus , which reduce approximately 20-30% yield of B. napus . It also could affect the oil and erucic acid content of B. napus , resulting in a reduction of the quality (Aggarwal et al. 1997; McCartney et al. 1999). Therefore, it is necessary to identify the resistant gene and breed varieties with S.sclerotiorumresistance in B. napus .
Glutathione S-transferases (GST) are belonging to the multifunctional protein family. In plants, GSTs are mainly divided into 14 classes, including phi (GSTF), tau (GSTU), theta (GSTT), zeta (GSTZ), lambda (GSTL), dehydroascorbate reductase (DHAR), tetrachloro hydroquinone dehalogenase (TCHQD), γ-subunit classes of the eukaryotic translation elongation factor 1B (EF1Bγ), hemerythrin (GSTH), ota (GSTI), metaxin, glutathionyl hydroquinone reductase (GHR), GSTs with two thioredoxins (GST2N), and microsomal prostaglandin E synthase type 2 (mPGES2) (Liu et al. 2013; Wei et al. 2019). The main functions of GSTs in plants include: (1) GSTs as the herbicide detoxification enzyme function in catalyzing the conjunction of glutathione (GSH) with the herbicides and reduce their toxicity (Edwards et al. 2000); (2) GSTs possess ligandin function and are responsible for the transport of anthocyanins and auxin (Droog et al. 1995; Jiang et al. 2019); (3) GSTs exhibit glutathione peroxidase activity, and catalyze the GSH and hydroperoxides form to GSSG and hydroxy derivatives, which could protects the plants from oxidative damage (Gullner et al. 2018; Edwards et al. 2000).
GST genes have been shown to play the great role in response to biotic and abiotic stress such as chilling, salt, drought (Roxas et al. 1997; Li et al. 2019; Liao et al. 2014). The cotton GST gene played the great role in Verticillium wilt resistance through balancing the production and scavenging of H2O2 (Li et al. 2019). In maize, aGST gene was found to be associated with resistance to multiple disease resistance, southern leaf blight, gray leaf spot and northern leaf blight caused by a specific amino acid substitution of GST (Wisser et al. 2011). Gullner et al. (2018) (Gullner et al. 2018) summarized the roles of plant GST genes in plant pathogen interactions, including basal resistance, HR-associated (hypersensitive response) resistance, limiting susceptibility and promoting susceptibility. However, the molecular mechanism ofGSTs in conferring pathogen resistance still need to be clarified.
In recent years, QTL mapping and transcriptome sequencing in B. napus have been used to identify pathways and genes associated with S. sclerotiorumresistance, including oxidative burst, Ca2+ signaling, jasmonic acid, as well as genes involved in glutathione metabolism (Bo et al. 2007; Zhao et al. 2007; Zhao et al. 2010; Mei et al. 2016; Wu et al. 2016). Several genes have been identified in B. napus with resistance to S. sclerotiorum , including BnWRKY33 (Wang et al. 2014), BnWRKY15 (Liu et al. 2018), BnNPR1 (Wang et al. 2020), BnCCR2 (Liu et al. 2021), BnMED16 (Hu et al. 2021). Lin et al., (2022) (Lin et al. 2022) identified the S. sclerotiorum -inducible promoter PBnGH17D in B. napus , which was used for genetic engineering of S. sclerotiorum resistance. However, the function and molecular mechanism of GST gene in response to S. sclerotiorum in B. napus have not been reported.
In previous study, we identified the candidate GST gene,BnGSTU12 , associated with sclerotiorum stem resistance using genome-wide association study (GWAS) and the expression levels ofBnGSTU12 in resistant lines were higher than that in susceptible lines (Wei et al. 2016). The expression of GST genes were up-regulated in B. napus after inoculation with S. sclerotiorum (Zhao et al. 2010). BnGSTU12 was homologous toAtGSTU12 in A. thaliana .AtGSTU12 was induced by flagellin peptide, but it was not induced by salicylic acid (Sappl et al. 2009). In the study, we aimed to investigate the function and resistance mechanism of BnGSTU12 in S. sclerotiorumresistance in B. napus . This study is not only important for the study of S. sclerotiorumresistance in B. napus , but also provides a new breeding strategy for cultivating resistant B. napus .