Search

Alternaria brassicicola(Ab) can cause a major yield and quality-limiting disease of Brassica oleraceacalled black spot, and the genetic resources conferring complete resistance against Abhave not been identified to date. Here, comparative transcriptome and targeted metabolome analysis were performed utilizing a newly identified resistant (R) line and a broccoli susceptible (S) line at 6, 24, and 72 h post-inoculation (hpi). Kyoto encyclopedia of genes and genomes pathway enrichment and the weighted gene co-expression network analyses showed that the phenylpropanoid pathway regulates the resistance to Abin broccoli. One metabolite, cinnamic acid, was significantly upregulated in the Ab_inoculated R line compared with the mock treatment but no significant difference in the S line, indicating that the cinnamic acid may cause the resistance difference between R and S lines. Our results also revealed that three indolic glucosinolates of I3G, 4MI3G, and 1MI3G were significantly increased in the Ab_inoculated R line compared with the mock treatment, and some related genes were differentially expressed between the R and S lines. These results provided new insights into the mechanism of Abdefense in B. oleraceaand have laid a theoretical foundation for effectively utilizing resistant germplasm resources in broccoli breeding.

Seeds of 32 pure lines and 6 commercial broccoli cultivars were used to investigate variation in glucosinolates and their breakdown products. The aliphatic glucosinolate content was 54.5–218.7 μmol/g fresh weight, accounting for >90% of the total glucosinolates. The major glucosinolates found were glucoraphanin and glucoerucin in 27 samples and progoitrin in 7 samples. A gas chromatography-flame ionization detector (GC-FID) method was used to identify glucosinolate breakdown products; nine products were directly determined using standards. Using Arabidopsis thalianalines myb28myb29and Landsberg erectato hydrolyze each reference glucosinolate, seven products were tentatively identified. 4-(Methylsulfinyl)butyl isothiocyanate and 5-(methylsulfinyl)pentanenitrile contents were 2.6–91.1 μmol/g fresh weight and 0–35.4 μmol/g fresh weight, respectively, with epithionitriles being more common than nitriles in accessions rich in alkenyl glucosinolate. Additionally, (S)-5-vinyl-1,3-oxazolidine-2-thione was detected in accessions rich in progoitrin. Specific lines with altered glucosinolate profiles and breakdown products were obtained and discussed according to the putative glucosinolate metabolism pathway.