Transcriptome Analysis of Chinese Cabbage Infected with Plasmodiophora Brassicae in the Primary Stage

Abstract

Clubroot disease caused by the infection of Plasmodiophora brassicae is widespread in China, and significantly reduces the yield of Chinese cabbage (Brassica rapa L. ssp. pekinensis). However, the resistance mechanism of Chinese cabbage against clubroot disease is still unclear. It is important to exploit the key genes that response to early infection of P. brassicae. In this study, it was found that zoospores were firstly invaded hair roots on the 8th day after inoculating with 1 × 10⁷ spores/mL P. brassicae. Transcriptome analysis found that the early interaction between Chinese cabbage and P. brassicae caused the significant expression change of some defense genes, such as NBS-LRRs and pathogenesis-related genes, etc. The above results were verified by quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Otherwise, peroxidase (POD) salicylic acid (SA) and jasmonic acid (JA) were also found to be important signal molecules in the resistance to clubroot disease in Chinese cabbage. This study provides important clues for understanding the resistance mechanism of Chinese cabbage against clubroot disease.

Fig. 1

The state of plant growth on the 8th day after being inoculated with different concentration of P. brassicae spore suspension.

Fig. 2

DEGs between the control (CK) and treatment (T) groups from three replicates of Chinese cabbage at the initial infection stage.

Fig. 3

GO analysis of DEGs between the control (CK) and treatment (T) groups of Chinese cabbage at the initial infection stage. The proportion of DEGs in the cellular component, biological process, and molecular function categories are shown. Red indicates up-regulated genes; green indicates down-regulated genes in the roots of T group.

Fig. 4

Top 20 terms of KEGG analysis of DEGs between the control (CK) and treatment (T) groups of Chinese cabbage at the initial infection stage. Orange indicates up-regulated genes; blue indicates down-regulated genes in the roots of T group.

Fig. 5

Heatmap of DEGs related to disease resistance between the control (CK) and treatment (T) groups of Chinese cabbage at the initial infection stage. Green indicates significantly up-regulated genes; red indicates significantly down-regulated genes in the roots of T group. Arrow represents DEGs with more than twofold difference.

Fig. 6

qRT-PCR analyzed of the differentially expressed disease resistance genes with more than twofold difference between control (CK) and treated (T, inoculated with P. brassicae) roots of Chinese cabbage at the initial infection stage. Data represent the mean ± standard deviation (n = 3); *The significance at p ≤ 0.05, maintain as student’s t test.

Fig. 7

POD-related (DEGs) between control (CK) and treated (T, inoculated with P. brassicae) roots of Chinese cabbage at the initial infection stage. (a) Heatmap of all significant POD-related DEGs. Green indicates significantly up-regulated genes; red indicates significantly down-regulated genes in the roots of T group. Arrow represents DEGs with more than a twofold difference. (b) qRT-PCR analysis for DEGs with more than twofold difference. Data represent the mean ± standard deviation (n = 3); The significance at p ≤ 0.05, maintain as student’s t test. c, POD activity in CK and T groups. Data represent the mean ± standard deviation (n = 3); *The significance at p ≤ 0.05, maintain as student’s t test.

Fig. 8

DEGs of SA and JA/ET signaling pathway between the control group (CK) and treatment group (T, inoculated with P. brassicae) of Chinese cabbage at the initial infection stage. (a) Heatmap of all significant DEGs of SA and JA/ET signaling. Green indicates significantly up-regulated genes; red indicates significantly down-regulated genes in the roots of T group. Arrow represents DEGs with more than a twofold difference. (b) qRT-PCR analysis for DEGs more than twofold. Data represent the mean ± standard deviation (n = 3); *The significance at p ≤ 0.05, maintain as student’s t test.

Fig. 9

A simplified schematic diagram of the resistance response of Chinese cabbage at the initial infection stage by P. brassicae.