Deciphering the role of Heavy metal-associated Isoprenylated Plant Proteins (HIPPs) massively interacting with MAX effectors in rice susceptibility to Magnaporthe oryzae (HIPP-HUB)

• Applicant: Dr. Svenja Saile
• Subject Area: Plant Breeding and Plant Pathology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 550008416

Plant diseases are a major problem in agriculture and a threat to global food security. A prime case is blast, the most destructive disease of cultivated rice worldwide and an emerging disease on wheat. This disease is caused by the fungal pathogen Magnaporthe oryzae, which harbors a huge collection of effector proteins, that are secreted during infection to target host cellular processes promoting fungal growth. The objective of the HIPP-HUB project is to gain a deeper understanding of the virulence mechanisms used by fungal pathogens to promote host colonization. I will address this goal by investigating Magnaporthe AVRs and ToxB-like (MAX) effectors, a large family of effectors that has particularly expanded in the blast fungus M. oryzae. I will build on the discovery of the host laboratory that MAX effectors massively interact with the heavy metal-associated (HMA) domain of multiple rice HMA domain-containing Plant Proteins (HPPs) and HMA domain-containing Isoprenylated Plant Proteins (HIPPs). Certain HMA domains of OsHIPPs interact with at least six different MAX effectors, suggesting that these OsHIPP effector hubs may be prime effector targets and play an essential role in host susceptibility. This hypothesis is supported by emerging evidence that H(I)PPs in rice and other plant species, act as susceptibility factors and are targeted by various effectors. Previous studies and my own experiments revealed that multiple HIPPs are localized at plasmodesmata (PD), pointing towards a putative role of HIPPs in contributing to PD function. Remarkably, PD can be exploited by effectors to move from infected cells to non-infected cells, likely to prepare surrounding cells before invasion. These findings suggest that PD-dependent cell-to-cell movement of effectors plays a crucial role in host susceptibility. Increasing evidence also indicates that effectors from diverse pathogens alter the function of PD in their host to enable effector cell-to-cell movement. Consistent with this, I observed that several MAX effectors are specifically recruited to PD in the presence of interacting HIPPs from rice. This leads to the hypothesis that OsHIPPs might act as cellular “gatekeepers”, and that MAX effectors might co-opt OsHIPP function to modify PD permeability. Using a combination of biochemical and cell biological approaches, the HIPP-HUB project will analyse (1) MAX/OsHIPP hub interactions in planta, (2) the association of OsHIPPs with PD, and (3) the role of OsHIPP hubs and MAX effectors in the control of PD-dependent protein cell-to-cell movement.

• DFG Programme: WBP Fellowship
• International Connection: France
• Host: Stella Cesari, Ph.D.