Key Receptors Work Together to Boost Tomato Plant Defenses

Jenn Hoskins
24th July, 2024

Key Receptors Work Together to Boost Tomato Plant Defenses

Image Source: Natural Science News, 2024

Key Findings

  • Researchers at Korea University discovered how the hormone systemin triggers defense responses in tomato plants
  • Systemin binds to the receptor SYR1, which then partners with SERK proteins to activate defense mechanisms
  • This activation involves mutual phosphorylation between SYR1 and SERKs, leading to the phosphorylation of TPK1b, a key protein in defense signaling
Systemin, the first peptide hormone identified in plants, plays a crucial role in mediating local and systemic wound-induced defense responses in tomato (Solanum lycopersicum). It is recognized by the leucine-rich-repeat receptor-like kinase (LRR-RLK) receptor SYSTEMIN RECEPTOR1 (SYR1). However, the exact mechanism by which systemin recognition translates into intracellular signaling pathways to trigger defense responses has remained elusive. Recent research from Korea University sheds light on this mechanism, demonstrating that SERK family LRR-RLKs function as co-receptors for SYR1 to mediate systemin signal transduction in tomato[1]. In this study, the researchers employed chemical genetic approaches and engineered receptors to reveal that the cytoplasmic kinase domains of SYR1 and SERKs undergo mutual trans-phosphorylation upon systemin binding. This interaction activates SYR1, which then induces a broad spectrum of defense responses. Systemin was found to promote the association between SYR1 and all tomato SERKs (SlSERK1, SlSERK3A, and SlSERK3B). The activation of these SYR1-SlSERK complexes leads to the phosphorylation of TOMATO PROTEIN KINASE 1B (TPK1b), a receptor-like cytoplasmic kinase previously shown to positively regulate systemin responses[2]. The study's findings are significant because they provide a clearer understanding of how systemin-mediated defense mechanisms are activated at the molecular level. The association of SYR1 and SlSERKs and their subsequent trans-phosphorylation appear to be critical steps in the signal transduction process. This discovery aligns with earlier research that indicated the importance of protein kinases in plant defense responses. For instance, TPK1b was previously shown to be involved in ethylene-mediated defense mechanisms against necrotrophic fungi and herbivorous insects[2]. The phosphorylation of TPK1b by the SYR1-SlSERK complex further supports its role in these defense pathways. Moreover, the study revealed that upon association with SYR1, SlSERKs are cleaved by the Pseudomonas syringae effector HopB1. This finding underscores the activation of SlSERKs by systemin-bound SYR1, adding another layer of complexity to the systemin signaling pathway. Genetic analysis using Slserk mutants confirmed that SlSERKs are essential for systemin-mediated defense responses, highlighting their critical role in the overall defense mechanism. This research builds on previous findings related to peptide hormones and their processing in plants. For example, earlier studies showed that the processing of prosystemin, a precursor of the wound hormone systemin, is carried out by phytaspases, aspartate-specific proteases. This processing is crucial for the biological activity of systemin and its ability to trigger systemic wound responses[3]. The current study complements these findings by elucidating the downstream signaling events that occur after systemin is recognized by its receptor, SYR1. Additionally, the study's insights into the role of LRR-RLKs in plant defense responses align with previous research on receptor kinases. LRR-RKs are known to regulate responses to various internal and external stimuli through phosphorylation events. The discovery that SYR1 and SERKs undergo mutual trans-phosphorylation to activate defense responses supports the notion that phosphorylation is a key regulatory mechanism in receptor kinase signaling[4]. In summary, the research from Korea University provides a comprehensive understanding of how systemin recognition by SYR1 and its co-receptors, the SERKs, activates defense responses in tomato plants. By demonstrating the mutual trans-phosphorylation of SYR1 and SERKs and the subsequent phosphorylation of TPK1b, this study offers valuable insights into the molecular mechanisms underlying plant defense against herbivorous insects and necrotrophic fungi. These findings not only advance our knowledge of plant hormone signaling but also have potential implications for developing strategies to enhance crop resistance to pests and pathogens.

GeneticsBiochemPlant Science

References

Main Study

1) SERKs serve as co-receptors for SYR1 to trigger systemin-mediated defense responses in tomato.

Published 23rd July, 2024

https://doi.org/10.1111/jipb.13747

Related Studies

2) Tomato protein kinase 1b mediates signaling of plant responses to necrotrophic fungi and insect herbivory.

https://doi.org/10.1105/tpc.108.059477

3) Phytaspase-mediated precursor processing and maturation of the wound hormone systemin.

https://doi.org/10.1111/nph.14568

4) Activation loop phosphorylation of a non-RD receptor kinase initiates plant innate immune signaling.

https://doi.org/10.1073/pnas.2108242118


Related Articles

An unhandled error has occurred. Reload 🗙