New Discoveries: Three Key Factors in the Fungus That Causes Plant Galls

Jenn Hoskins
19th July, 2024

New Discoveries: Three Key Factors in the Fungus That Causes Plant Galls

This experiment pinpoints how three newly discovered proteins from the corn smut fungus (Ustilago maydis) hijack a key maize (Zea mays) protein, revealing they all bind specifically to one end of it—the N-terminal domain (b)—while ignoring the other.

Image adapted from: Khan et al. / CC BY (Source)

Key Findings

  • Researchers from the University of Bonn identified three new effector proteins (Tip6, Tip7, Tip8) from Ustilago maydis that interact with the maize TPL protein RELK2
  • Tip6 and Tip7 interact with RELK2 in the nucleus, while Tip8 interacts outside the nucleus and can trigger cell death in non-host plants
  • Tip6 and Tip7 enhance the virulence of U. maydis, showing they play distinct roles in the infection process
Ustilago maydis, a biotrophic pathogen, is responsible for smut disease in maize. The pathogen secretes a variety of effector proteins that target host proteins during infection. Researchers from the University of Bonn have recently identified three novel effector proteins that interact with the maize TOPLESS (TPL) protein RAMOSA 1 ENHANCER LOCUS 2 LIKE 2 (RELK2)[1]. This study builds upon earlier research that has shown the role of TPL proteins in plant susceptibility to pathogens[2]. The study screened 297 effector candidates from U. maydis for their ability to interact with the maize TPL protein RELK2. They identified three new TPL-interacting proteins, named Tip6, Tip7, and Tip8. These proteins have been shown to induce auxin signaling, a crucial plant hormone pathway involved in growth and stress responses. Structural modeling and mutational analysis revealed specific motifs in Tip6 and Tip7 responsible for interacting with TPL proteins. The interaction between Tip6 and Tip7 with RELK2 primarily occurs in the nuclear compartments of the plant cells. In contrast, Tip8 colocalizes with RELK2 in a compartment outside the nucleus. Remarkably, overexpression of Tip8 in non-host plants leads to cell death, suggesting that the plant recognizes the effector or its activity as a threat. This indicates that Tip8 might have a role in triggering plant immune responses. Further infection assays with single and multideletion mutants of U. maydis demonstrated that Tip6 and Tip7 contribute positively to the pathogen's virulence. This finding is significant because it shows that these effectors are not merely redundant but have distinct roles in the infection process. Transcriptional profiling of maize leaves infected with Tip effector mutants compared to the SG200 strain of U. maydis provided additional evidence supporting the unique activities of these effectors. This study ties into previous findings on the role of TPL proteins in plant-pathogen interactions. Earlier research identified that TPL proteins in tomato and Arabidopsis are targeted by pathogenic effectors, leading to increased susceptibility to Fusarium wilt diseases[2]. This suggests that TPL proteins are a common target for various pathogens, making them a crucial component in understanding plant immunity. Moreover, the study's identification of protein-protein interactions between effectors and host proteins aligns with previous research on the complexity of effector interactions in plant-pathogen relationships. For example, U. maydis effectors have been shown to form complexes that can manipulate the host’s immune network[3]. This adds another layer of complexity to how pathogens overcome plant defenses. Additionally, the study highlights the importance of protein-protein interactions in integrating various signaling pathways, including those mediated by phytohormones like auxin[4]. Understanding these interactions can provide insights into how plants coordinate their responses to biotic stresses and could lead to the development of crops with enhanced resistance to pathogens. In conclusion, the study by the University of Bonn expands our understanding of how U. maydis effectors interact with maize TPL proteins to promote virulence. By identifying specific effector proteins and their interaction motifs, the research provides valuable insights into the molecular mechanisms underlying plant-pathogen interactions. This knowledge could be instrumental in developing new strategies for enhancing crop resistance to diseases.

BiotechPlant ScienceMycology

References

Main Study

1) Tip of the iceberg? Three novel TOPLESS-interacting effectors of the gall-inducing fungus Ustilago maydis.

Published 17th July, 2024

https://doi.org/10.1111/nph.19967

Related Studies

2) Specific members of the TOPLESS family are susceptibility genes for Fusarium wilt in tomato and Arabidopsis.

https://doi.org/10.1111/pbi.14183

3) Systematic Y2H Screening Reveals Extensive Effector-Complex Formation.

https://doi.org/10.3389/fpls.2019.01437

4) Extensive signal integration by the phytohormone protein network.

https://doi.org/10.1038/s41586-020-2460-0


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