| Plant diseases caused by fungi are considered to be important factors that severely limit food production. Brassica species such as canola, one of the important agricultural crops, are affected by several abiotic and biotic stresses. Phoma stem canker (also known as blackleg) and Alternaria blackspot of canola caused by Leptosphaeria maculans and Alternaria brassicae, respectively are important diseases of canola. In the case of blackleg, resistant varieties of canola were developed but resistance breakdown has been observed due to the evolution of pathogenic isolates of L. maculans. Resistance to blackspot disease has not been identified in Brassica species. Therefore, elucidating the details of fungal-plant pathogenesis, including the molecular mechanisms of these diseases and the nature of the host cellular response is important. In recent years, proteomic analysis has emerged as a powerful approach to study, not only defense-related proteins that are induced in pathogen-challenged plants to overcome disease, but also proteins that are produced by phytopathogens and serve as virulence or pathogenicity factors. We performed a proteome-level investigation with different disease-susceptible and -tolerant Brassica species using two-dimensional electrophoresis (2-DE) and mass spectrometry (MS). Several proteins identified in these studies were those with antioxidant activity, photosynthesis-related and other metabolic enzymes. The expression of genes encoding some of these proteins was studied using quantitative real-time PCR (q-RT-PCR) and Western blotting. Our findings suggested that disease-tolerant plants appear to activate a large group of antioxidant enzymes and pathways involved in the reinforcement of plant cell walls. Proteome-level studies were also conducted to understand the possible basis for differential virulence between two isolates of A. brassicae varying in their virulence. The distinct protein profiles obtained from these studies may help to reveal the nature of the molecular determinants of virulence that could be further exploited to identify pathogenicity factors and novel targets for managing disease. We also investigated the effects of cytokinins on the two pathogens. Our in planta results suggest the delayed onset of both diseases by the exogenous application of cytokinin. Our results may have important bearing on the development of novel crop protection strategies. |
