Expression profiling, biochemical and histochemical analysis of contrasting cultivars provide insight into resistance against white rust disease (Albugo candida) in Brassica juncea L

Background White rust disease caused by the biotrophic oomycete Albugo candida is one of the most serious impediments in realizing the production potential of Brassica juncea . Moreover, due to the obligate nature of the pathogen, R-gene-based resistance is unstable as the newer virulent races emerge quickly. Therefore, a deeper understanding of the molecular basis of resistance is essential for developing durable resistant varieties. In this study, we selected susceptible cultivar, ‘Pusa Jaikisan’ and its single R-gene-based resistant NIL, ‘Pusa Jaikisan WRR ’ for elucidating the defense mechanism in B. juncea against A. candida . Results Comparative histochemical analysis at 12 dpi showed higher callose deposition in the resistant cultivar than in the susceptible cultivar which hints towards its possible role in defense mechanism. Based on the biochemical markers observation, total protein was found to have a negative correlation with the resistance. The antioxidant enzymes (POX, CAT, and SOD) and non-enzymatic ROS scavenging compounds such as polyphenols and proline showed a positive correlation with the white rust resistance. The PPO, total chlorophyll and total carotenoids were also found to show higher activity in the ‘Pusa Jaikisan WRR ’. According to the heat map analysis, PAL was identified to be the most induced enzyme involved in the defense mechanism. Furthermore, the expression analyses of defense related markers such as salicylic acid (SA) associated PR protein genes ( PR1 and PR2 ) and jasmonic acid (JA) associated PR protein genes ( PR3 and PR12 ) were done by qRT-PCR. Based on the results, PR2 emerged as the best possible gene for defense against A. candida followed by PR1 . PR3 and PR12 also showed positive correlation with the disease resistance which may be due to the JA pathway acting complementary to the SA pathway, thus indicating a synergistic JA-SA hormonal crosstalk in case of B. juncea - A. candida interaction. Conclusion The present study establishes a major role of simulated response of the defense molecules which can stop the disease progression thus incurring resistance. This may be used in the future for developing resistance against the biotrophic pathogen especially A. candida in B. juncea .