The Plant Hippo Pathway: An Evolved Hub for Strategic Resource Allocation Governing Growth-Defence-Reproduction Trade-Offs.

For sessile plants, survival hinges on the dynamic allocation of limited resources among growth, defence and reproduction. We propose that the plant Hippo signalling network has evolved into a central strategic hub governing these fundamental trade-offs. Building upon its evolutionarily conserved pleiotropic roles, this hub in plants has acquired unique regulatory capacities. It integrates hormonal, developmental and stress signals to act as a cellular decision-maker, exhibiting organizational complexity that includes parallel branches and context-specific outputs. Plant-specific innovations-including a direct SIK1-MOB1 interaction that bypasses the canonical SAV1 scaffold, dual-specificity NDR kinases and MOB1A/B heterodimer formation-underpin this adaptive evolution. Crucially, the antagonism between SIK1 and MOB1 fine-tunes the jasmonate pathway, functioning as a molecular 'rheostat' for the growth-defence balance. Viewing the plant Hippo pathway through the lens of 'adaptive trade-off management' not only redefines its biological significance but also charts a new research agenda. We outline priorities to quantify signal flux through the hub, resolve the structure of plant-specific complexes and manipulate this decision-making system to engineer crops with optimized resilience and yield.