Abstract
Plasmodiophora brassicae, an obligate biotrophic pathogen-causing clubroot disease, can seriously affect Brassica crops worldwide, especially Chinese cabbage. Understanding the transcriptome and metabolome profiling changes during the infection of P. brassicae will provide key insights in understanding the defense mechanism in Brassica crops. In this study, we estimated the phytohormones using targeted metabolome assays and transcriptomic changes using RNA sequencing (RNA-seq) in the roots of resistant (BrT24) and susceptible (Y510-9) plants at 0, 3, 9, and 20 days after inoculation (DAI) with P. brassicae. Differentially expressed genes (DEGs) in resistant vs. susceptible lines across different time points were identified. The weighted gene co-expression network analysis of the DEGs revealed six pathways including “Plant–pathogen interaction” and “Plant hormone signal transduction” and 15 hub genes including pathogenic type III effector avirulence factor gene (RIN4) and auxin-responsive protein (IAA16) to be involved in plants immune response. Inhibition of Indoleacetic acid, cytokinin, jasmonate acid, and salicylic acid contents and changes in related gene expression in R-line may play important roles in regulation of clubroot resistance (CR). Based on the combined metabolome profiling and hormone-related transcriptomic responses, we propose a general model of hormone-mediated defense mechanism. This study definitely enhances our current understanding and paves the way for improving CR in Brassica rapa.
Highlights
Clubroot is a soil-borne disease caused by Plasmodiophora brassicae, an obligate biotrophic protist that infects cultivated and wild species of Brassicaceae family, including Chinese cabbage, cabbage, radish, cauliflower, and mustard, etc. (Howard et al, 2010)
At 20 days after inoculation (DAI), conspicuous irregular swelling was observed in the roots of S-line, whereas no signs of swelling were found in the roots of R-line (Figure 1)
These results indicate that clubroot develops more rapidly and severely on the susceptible genotype
Summary
Clubroot is a soil-borne disease caused by Plasmodiophora brassicae, an obligate biotrophic protist that infects cultivated and wild species of Brassicaceae family, including Chinese cabbage, cabbage, radish, cauliflower, and mustard, etc. (Howard et al, 2010). The dormant spores of P. brassicae are highly persistent and may remain infectious in the soil for up to 20 years (Dixon, 2009; Kageyama and Asano, 2009) This disease causes serious damage to crop quality and yield resulting in a global yield loss of 10–15% in Brassicaceae plants (Dixon, 2009). ETI is mediated by intracellular receptors encoded by plant disease resistance genes (R genes) that recognize the effector proteins and subsequently activate downstream immune responses to prevent pathogen infection (Sagi et al, 2017). We study the changes in the metabolome profiling and hormone-related transcriptomic at different stages of clubroot development in the contrastingly resistant B. rapa genotypes. Our results provide new insights into the root transcriptome- and phytohormone-mediated defense responses at different stages of clubroot disease in B. rapa
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