CsMYB60 Confers Enhanced Resistance to Fusarium solani by Increasing Proanthocyanidin Biosynthesis in Cucumber

Root rot caused by Fusarium solani is one of the most common fungal diseases in cucumber (Cucumis sativus). Proanthocyanidins (PAs) are known to play important roles in inhibiting the growth of phytopathogens. In addition, CsMYB60 is a known positive regulator of flavonol and PA biosynthesis in cucumber. However, it remains unclear that whether PAs can inhibit the growth of F. solani and whether CsMYB60 serves as a target gene for increasing resistance to phytopathogens in cucumber. In this study, we demonstrated that PAs (or their building block, catechin) could increase the resistance of cucumber seedlings to F. solani both in vitro and in vivo. The addition of catechins, or crude leaf extracts treated with different concentrations of catechins in culture medium, could significantly inhibit the hyphal growth of F. solani. On the other hand, cucumber seedlings treated with catechins showed higher resistance to F. solani than the seedlings of control group. Moreover, transgenic cucumber seedlings overexpressing CsMYB60, with the observed accumulation of PAs, were more resistant to F. solani than the nontransgenic siblings. Therefore, our results suggest that PAs (or catechin) can serve as a biological control agent to protect cucumber plants from the infection of F. solani. More importantly, CsMYB60 holds great promise as a target gene to confer disease resistance during the molecular breeding in cucumber.