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

Systemin, the first peptide hormone identified in plants, was initially isolated from tomato (Solanum lycopersicum) leaves. Systemin mediates local and systemic wound-induced defense responses in plants, conferring resistance to necrotrophic fungi and herbivorous insects. Systemin is recognized by the leucine-rich-repeat receptor-like kinase (LRR-RLK) receptor SYSTEMIN RECEPTOR1 (SYR1), but how the systemin recognition signal is transduced to intracellular signaling pathways to trigger defense responses is poorly understood.

ZTL regulates thermomorphogenesis through TOC1 and PRR5.

Plants adapt to high temperature stresses through thermomorphogenesis, a process that includes stem elongation and hyponastic leaf growth. Thermomorphogenesis is gated by the circadian clock through two evening-expressed clock components, TIMING OF CAB EXPRESSION1 (TOC1) and PSEUDO-RESPONSE REGULATORS5 (PRR5). These proteins directly interact with and inhibit PHYTOCHROME INTERACTING FACTOR4 (PIF4), a basic helix-loop-helix transcription factor that promotes thermoresponsive growth.

Overexpression of Promotes Thermomorphogenesis Through the PRR5-PIF4 Pathway.

Thermomorphogenesis is the morphological response of plants to an elevation in the ambient temperature, which is mediated by the bHLH transcription factor PIF4. The evening-expressed clock component, PRR5, directly represses the expression of mRNA. Additionally, PRR5 interacts with PIF4 protein and represses its transactivation activity, which in turn suppresses the thermoresponsive growth in the evening.