Many economically important crops and vegetables belonging to the cruciferous family are heavily endangered by clubroot disease caused by Plasmodiophora brassicae infection. Breeding of clubroot resistant cultivars based on mapping and cloning of resistant genes is commonly regarded as the most cost-effective and efficient way to fight against this disease. The traditional way of R gene functional validation requires stable transformation that is both time- and labor-consuming. In this study, a rapid and efficient hairy-root transgenic protocol mediated by Agrobacterium rhizogenes was developed. The transformation positive rate was over 80% in Brassica napus showed by GUS reporter gene and this transformation only took 1/6 of the time compared with stable transformation. The system was applicable to different B. napus varieties and other cruciferous crops including Brassica rapa and Brassica oleracea. In particular, two known CR genes, CRA3.7.1 and CRA8.2.4 were used respectively, as example to show that the system works well for CR gene study combined with subsequent P. brassicae infection in B. napus. Most importantly, it works both in over-expression that led to disease resistance, as well as in RNAi which led to disease susceptible phenotype. Therefore, this system can be used in batch-wise identification of CR genes, and also offered the possibility of manipulating key genes within the P. brassicae genome that could improve our knowledge on host–pathogen interaction.

Cassava, Manihot esculenta Crantz (Me), is a major dietary source of calories for over 700 million people in tropical regions. The production of cassava is constantly threatened by cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis (Xam). The gene resources for CBB-resistant breeding of cassava are limited. In model plant species, ethylene response factors play important roles in response to pathogen infection. In this study, cassava ethylene response factors (MeERFs) were identified and characterized as the first step in studying their potential for CBB-resistant breeding of cassava. In the cassava genome 155 MeERFs were identified, of which 23 were induced by Xam infection. The promoter regions of 204 genes harbored GCC-box that had the potential to interact with MeERFs. Using 37 transcriptomes derived from Xam infection treatment, four gene co-expression modules for the MeERFs and GCC-box containing genes were constructed. Six MeERFs were associated with two GCC-box containing genes: transcription initiation factor TFIIE subunit beta (MeTFIIE), and histone-lysine N-methyltransferase ASHR1 (MeASHR1). Dual-luciferase reporter assays showed that MeERF10 and MeERF58 positively regulated MeTFIIE; MeERF137 negatively regulated MeTFIIE; MeERF10 and MeERF137 positively regulated MeASHR1; and MeERF35 negatively regulated MeASHR1. The four MeERFs may mediate pathogen response by regulating the expression of the two GCC-box containing genes.