Abstract
Sclerotinia stem rot (white mold), caused by the fungus Sclerotinia sclerotiorum, is a serious disease of Brassica crops worldwide. Despite considerable progress in investigating plant defense mechanisms against this pathogen, which have revealed the involvement of glucosinolates, the host–pathogen interaction between cabbage (Brassica oleracea) and S. sclerotiorum has not been fully explored. Here, we investigated glucosinolate profiles and the expression of glucosinolate biosynthesis genes in white-mold-resistant (R) and -susceptible (S) lines of cabbage after infection with S. sclerotiorum. The simultaneous rise in the levels of the aliphatic glucosinate glucoiberverin (GIV) and the indolic glucosinate glucobrassicin (GBS) was linked to white mold resistance in cabbage. Principal component analysis showed close association between fungal treatment and cabbage GIV and GBS contents. The correlation analysis showed significant positive associations between GIV content and expression of the glucosinolate biosynthesis genes ST5b-Bol026202 and ST5c-Bol030757, and between GBS content and the expression of the glucosinolate biosynthesis genes ST5a-Bol026200 and ST5a-Bol039395. Our results revealed that S. sclerotiorum infection of cabbage induces the expression of glucosinolate biosynthesis genes, altering the content of individual glucosinolates. This relationship between the expression of glucosinolate biosynthesis genes and accumulation of the corresponding glucosinolates and resistance to white mold extends the molecular understanding of glucosinolate-negotiated defense against S. sclerotiorum in cabbage.
Highlights
White mold caused by the fungal pathogen Sclerotinia sclerotiorum infects more than 400 plant species, including important crops such as sunflower, chickpea and rapeseed [1,2]
One line, SCNU-C-049, exhibited complete resistance with no disease symptoms, while the other 44 lines were susceptible to S. sclerotiorum, as evidenced by changes visible at 5 days post inoculation (DPI) (Supplementary File S1)
Another study conducted by our group had previously produced a sample illustrative spectrum by mass spectrometry analysis of samples from cabbage lines that were resistant and susceptible to a different pathogen, ringspot (Mycosphaerella brassicicola), and used it to identify individual glucosinolate compounds found in cabbage leaves [38]
Summary
White mold caused by the fungal pathogen Sclerotinia sclerotiorum infects more than 400 plant species, including important crops such as sunflower, chickpea and rapeseed [1,2]. Scientists have identified resources with high levels of resistance against S. sclerotiorum from wild Brassica oleracea [10], one of the parental species of rapeseed. This finding brings new hope for improving S. sclerotiorum resistance of rapeseed, especially since its wild relatives, such as Brassica rupestris, Brassica incana, Brassica insularis, and Brassica villosa, show high levels of resistance [10]. GSL metabolism is a potentially fruitful source of pathogen-resistance genes
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