Cytosolic WPRa4 and Plastoskeletal PMI4 Proteins Mediate Touch Response in a Model Organism Arabidopsis

Plastoskeletal PMI4 Protein is a Key Regulator of ThigmomorphogenesisTo elucidate the early signaling components involved in thigmomorphogenesis in Arabidopsis thaliana, we combined microscopy and proximity-labeling (PL)-based quantitative biotinylproteomics to characterize the touch-responsive putative cytoskeleton-interacting protein WPRa4 (TREPH1). Our findings revealed that WPRa4 localizes near plastids and interacts with cytosolic Plastid Movement-Impaired (PMI) proteins and a plastidic translocon component, suggesting a cytoskeleton-plastid network in mechanosensing. Bioinformatic analysis of PL and cross-linking mass spectrometry (XL-MS) data identified PMI4 as a key mediator, with pmi4 mutants lacking touch-induced bolting delay, rosette size reduction, and Ca²⁺ oscillations. Transcriptomics further showed that PMI4 regulates touch-responsive and jasmonic acid (JA)associated genes, such as LOX2. We propose a molecular model where interconnected Cytoskeleton-Plastoskeleton Continuum (CPC) proteins act as early mechanosensors, integrating the touch responses of plant aerial organs with calcium signaling and transcriptional reprogramming in Arabidopsis.