Phytophthora infestans RXLR effector Pi04089 perturbs diverse defense-related genes to suppress host immunity.

Background: The oomycete pathogen secretes many effectors into host cells to manipulate host defenses. For the majority of effectors, the mechanisms related to how they alter the expression of host genes and reprogram defenses are not well understood. In order to investigate the molecular mechanisms governing the influence that the Phytophthora infestans RXLR effector Pi04089 has on host immunity, a comparative transcriptome analysis was conducted on Pi04089 stable transgenic and wild-type potato plants.

Results: Potato plants stably expressing Pi04089 were more susceptible to P. infestans. RNA-seq analysis revealed that 658 upregulated genes and 722 downregulated genes were characterized in Pi04089 transgenic lines. A large number of genes involved in the biological process, including many defense-related genes and certain genes that respond to salicylic acid, were suppressed. Moreover, the comparative transcriptome analysis revealed that Pi04089 significantly inhibited the expression of many flg22 (a microbe-associated molecular pattern, PAMP)-inducible genes, including various Avr9/Cf-9 rapidly elicited (ACRE) genes. Four selected differentially expressed genes (StWAT1, StCEVI57, StKTI1, and StP450) were confirmed to be involved in host resistance against P. infestans when they were transiently expressed in Nicotiana benthamiana.

Conclusion: The P. infestans effector Pi04089 was shown to suppress the expression of many resistance-related genes in potato plants. Moreover, Pi04089 was found to significantly suppress flg22-triggered defense signaling in potato plants. This research provides new insights into how an oomycete effector perturbs host immune responses at the transcriptome level.