Variz, H. | Search bioRxiv

bioRxiv2023

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

The 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 of P. pachyrhizi effector candidate 15 (PpEC15), an aspartic protease, leads to enhanced bacterial growth in 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 of PpEC15 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 putative PpEC15 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 that PpEC15 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 that PpEC15 is conserved across P. pachyrhizi isolates and other economically important rust species and is involved in the suppression of plant basal defense responses. Understanding the role of PpEC15 in P. pachyrhizi virulence will provide a foundation for designing targeted intervention strategies to generate rust-resistant crops.

plant biology↗

bioRxiv2020

Plasmodesmata-dependent intercellular movement of bacterial effectors

Pathogenic microorganisms deliver protein effectors into host cells to suppress host immune responses. Recent findings reveal that phytopathogens manipulate the function of plant cell-to-cell communication channels plasmodesmata (PD) to promote diseases. Several bacterial and filamentous pathogen effectors have been shown to regulate PD in their host cells. A few effectors of filamentous pathogens have been reported to move from the infected cells to neighboring plant cells through PD; however, it is unclear whether bacterial effectors can traffic through PD in plants. In this study, we systemically determined the intercellular movement of Pseudomonas syringae pv. tomato (Pst) DC3000 effectors between adjoining plant cells in Nicotiana benthamiana. We observed that at least 16 Pst DC3000 effectors move from transformed cells to the surrounding plant cells. The movement of the effectors is largely dependent on their molecular weights. The expression of PD regulators, Arabidopsis PD-located protein PDLP5 and PDLP7, lead to PD closure and inhibits the PD-dependent movement of a bacterial effector in N. benthamiana. Similarly, a 22-amino acid peptide of bacterial flagellin (flg22) treatment induces PD closure and suppresses the movement of a bacterial effector in N. benthamiana. Together, our findings demonstrated that bacterial effectors are able to move intercellularly through PD in plants.

plant biology↗