A soybean rust effector protease suppresses host immunity and cleaves a 3-deoxy-7-phosphoheptulonate synthase

Abstract

AbstractThe devastating soybean rust (SBR) pathogen,Phakopsora pachyrhizi, encodes many secreted proteins, but only two have been functionally characterized for their roles in rust virulence. Here, we demonstrate that transient expression ofP. pachyrhizieffector candidate 15 (PpEC15), an aspartic protease, leads to enhanced bacterial growthin planta, suppression of callose deposition, reduced expression of plant defense-related marker genes and suppression of pathogen-associated molecular pattern (PAMP)-induced reactive oxygen species (ROS). Stable expression ofPpEC15 in soybean suppresses PAMP-induced ROS production and enhances bacterial growth, indicating that, collectively,PpEC15 suppresses host and non-host innate immune responses. Yeast-two-hybrid and proximity labeling identified putativePpEC15 interacting partners including a peptide-chain release factor (PCRF), a NAC83 (NAM, ATAF, and CUC) transcription factor, and a DAHP (3-deoxy-7-phosphoheptulonate) synthase. We further show thatPpEC15 can cleave DAHP but does not cleave PCRF or NAC83. Virus-induced gene silencing of NAC83, PCRF and DAHP altered PAMP-induced ROS production and salicylic acid production, indicating that these proteins may be involved in immune signaling. Collectively, our data show thatPpEC15 is conserved acrossP. pachyrhiziisolates and other economically important rust species and is involved in the suppression of plant basal defense responses. Understanding the role ofPpEC15 inP. pachyrhizivirulence will provide a foundation for designing targeted intervention strategies to generate rust-resistant crops.