Expression analysis of major genes involved in signaling pathways during infection of Chinese cabbage with Hyaloperonospora brassicae

• Infection was performed on Chinese cabbage with Hyaloperonospora brassicae.
• Upon infection, only the resistant line exhibited a hypersensitive response.
• Expression changes of genes involved in signaling pathways were compared.
• Resistance in T12–19 is characterized by SA signaling transduction.
• SA signaling pathways in T12–19 followed an R-gene-dependent defense mode.

The downy mildew caused by Hyaloperonospora brassicae is a destructive disease for Chinese cabbage (Brassica rapa L. sp. pekinensis), and very few studies have focused on disease resistance mechanisms in this economically important crop. Artificial infection was performed on leaves of resistant and susceptible Chinese cabbage lines with two distinct isolates of H. brassicae. Upon infection with H. brassicae, the resistant line T12–19 initially exhibited a HR. The susceptible line 91–112 did not have hypersensitive response (HR) and showed disease symptoms at initial stages. Plant responses and changes in the expression profiles of genes involved in signaling pathways were compared during the development of infection. Significant differences were found in early transcriptional changes of genes involved in salicylic acid (SA) signaling pathway in line T12–19, but not in the jasmonic acid (JA)/ethylene (ET) signaling pathway. In contrast, early transcriptional changes in the susceptible line 91–112 indicate a weak and abortive basal defense response. Collectively, our results suggest that the mechanism of resistance to downy mildew in resistant Chinese cabbage was in accord with the gene-for-gene model, and the resistance gene activated the SA signaling pathway predominantly to prevent pathogen colonization. However, this does not preclude JA and ET-mediated basal defenses from playing a role in downy mildew resistance.