Abstract
Ringspot, caused by the fungus Mycosphaerella brassicicola, is a serious disease of Brassica crops worldwide. Despite noteworthy progress to reveal the role of glucosinolates in pathogen defense, the host–pathogen interaction between cabbage (Brassica oleracea) and M. brassicicola has not been fully explored. Here, we investigated the glucosinolate profiles and expression of glucosinolate biosynthesis genes in the ringspot-resistant (R) and susceptible (S) lines of cabbage after infection with M. brassicicola. The concomitant rise of aliphatic glucoiberverin (GIV) and indolic glucobrassicin (GBS) and methoxyglucobrassicin (MGBS) was linked with ringspot resistance in cabbage. Pearson’s correlation and principle component analysis showed a significant positive association between GIV contents and the expression of the glucosinolate biosynthesis gene ST5b-Bol026202 and between GBS contents and the expression of the glucosinolate biosynthesis gene MYB34-Bol017062. Our results confirmed that M. brassicicola infection induces the expression of glucosinolate biosynthesis genes in cabbage, which alters the content of individual glucosinolates. This link between the expression of glucosinolate biosynthesis genes and the accumulation of their respective glucosinolates with the resistance to ringspot extends our molecular sense of glucosinolate-negotiated defense against M. brassicicola in cabbage.
Highlights
Ringspot is a common fungal disease of cabbage (Brassica oleracea) that causes economic losses worldwide [1,2]
Inoculation of cabbage leaves with M. brassicicola isolate IPO-99008 resulted in different responses in the 26 cabbage lines based on the scoring criteria of ringspot disease symptoms (Table 1, Figures S1 and S3)
Disease progression was determined in the R line BN4072, and the S line, BN3449, up to 30 days after inoculation (DAI) (Figure 1)
Summary
Ringspot is a common fungal disease of cabbage (Brassica oleracea) that causes economic losses worldwide [1,2]. The effects of GSL metabolism, and sulfur and nitrogen nutrition have been studied because brassica crops contain large amounts of sulfur-containing amino acids and GSLs [27,28,29,30]. A survey of the levels of GSLs in different brassica varieties showed alterations to the GSL profile at the time of inoculation by fungal pathogens. These changes were mainly due to an increase in aliphatic, indolic, and aromatic GSLs. In general, GSL degradation products induce the plant defense response against pathogens and general herbivores (Rask et al, 2000; Barth and Jander, 2006). An association between GSL levels and resistance to various fungal pathogens in brassicas has not yet been established [36]
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