Abstract
The disease caused by Sclerotinia sclerotiorum has traditionally been difficult to control, resulting in tremendous economic losses in oilseed rape (Brassica napus). Identification of important genes in the defense responses is critical for molecular breeding, an important strategy for controlling the disease. Here, we report that a B. napus mitogen-activated protein kinase gene, BnaMPK3, plays an important role in the defense against S. sclerotiorum in oilseed rape. BnaMPK3 is highly expressed in the stems, flowers and leaves, and its product is localized in the nucleus. Furthermore, BnaMPK3 is highly responsive to infection by S. sclerotiorum and treatment with jasmonic acid (JA) or the biosynthesis precursor of ethylene (ET), but not to treatment with salicylic acid (SA) or abscisic acid. Moreover, overexpression (OE) of BnaMPK3 in B. napus and Nicotiana benthamiana results in significantly enhanced resistance to S. sclerotiorum, whereas resistance is diminished in RNAi transgenic plants. After S. sclerotiorum infection, defense responses associated with ET, JA, and SA signaling are intensified in the BnaMPK3-OE plants but weakened in the BnaMPK3-RNAi plants when compared to those in the wild type plants; by contrast the level of both H2O2 accumulation and cell death exhibits a reverse pattern. The candidate gene association analyses show that the BnaMPK3-encoding BnaA06g18440D locus is a cause of variation in the resistance to S. sclerotiorum in natural B. napus population. These results suggest that BnaMPK3 is a key regulator of multiple defense responses to S. sclerotiorum, which may guide the resistance improvement of oilseed rape and related economic crops.
Highlights
Oilseed rape (Brassica napus L.) is an agriculturally important oilseed crop that is cultivated worldwide, including North America, Europe, and South Asia
The results suggest that altered expression of B. napus MPK3 (BnaMPK3) affects the pathogen-induced defense responses including reactive oxygen species (ROS) accumulation, cell death and expression of defense genes associated with salicylic acid (SA), jasmonic acid (JA), and ET defense signaling in BnaMPK3-OE and BnaMPK3-RNA interfering (RNAi) plants, and the expression of these defense responses is generally in an inverse pattern between the BnaMPK3-OE and the BnaMPK3-RNAi plants
We provide new data that enlarge the understanding of MPK3 functions, indicating that BnaMPK3, an MPK3 ortholog in B. napus, plays an important role in the defense against S. sclerotiorum, the most important pathogen of the crop
Summary
Oilseed rape (Brassica napus L.) is an agriculturally important oilseed crop that is cultivated worldwide, including North America, Europe, and South Asia. S. sclerotiorum is a hugely destructive necrotrophic fungal plant pathogen that is capable of causing disease on at least 408 described plant species, including many economically important crops, and more than 60 names have been used to refer to diseases caused by this fungal pathogen in agriculture (Bolton et al, 2006) This necrotrophic pathogen exhibits little host specificity, and research on the molecular aspects underlying the interactions that it established with host plants have been mainly concentrated on fungal pathogenesis, which has revealed several virulence mechanisms of this pathogen, including secretion of numerous cell wall degrading enzymes, production of the nonhost-selective toxin oxalic acid and secretion of effector proteins during infection (Riou et al, 1991, 1992; Cessna et al, 2000; Rollins and Dickman, 2001; Kim et al, 2008; Williams et al, 2011; Kabbage et al, 2013; Zhu et al, 2013; Guyon et al, 2014; Wang et al, 2015, 2018). These data imply that the defense responses to the pathogen involve a multiple and complicated arrange of signaling pathways
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