Quantitative and Hierarchical Coordination of Growth and Defence in Tomato (Solanum lycopersicum L.) Under Increasing...

Plants continuously face environmental challenges that require balancing growth and defence, two often antagonistic processes. Understanding how plants integrate these responses is crucial for improving stress resilience. Here, we investigated tomato (Solanum lycopersicum L.) responses to a gradient of mechanical wounding (0x, 1x, 3x, 5x and 10x wounds) using integrated phenotypic, metabolic, hormonal, and transcriptomic analyses. Increasing stress progressively shifted plant physiology from growth toward defence states, marked by graded inhibition of growth and flowering and proportional reinforcement of defensive traits. Hormonal analyses identified jasmonic acid (JA) as a central regulator of this transition, displaying rapid accumulation at low stress levels and saturation at moderate intensities. Transcriptomic analyses revealed a conserved JA-associated wound-responsive core activated across all treatments, whereas higher stress intensities recruited additional regulatory layers associated with defence amplification and growth repression. Transcription factor profiling further showed that this conserved regulatory backbone is dominated by ERF, bHLH, MYB and WRKY regulators, while stronger wound intensities progressively recruit distinct regulators. Together, our findings demonstrate that growth-defence coordination operates along a hierarchical continuum governed by quantitative stress thresholds rather than a binary switch, providing mechanistic insight into how plants dynamically fine-tune developmental and defence programmes under escalating stress.