Symbiotic phosphate transporter dynamics in rice expose functional plasticity of the arbuscules

Mutualism in the symbiosis between arbuscular mycorrhizal fungi and plants is based upon the exchange of carbon for soil minerals, with phosphate being of central importance. The exchange of nutrients occurs when the fungus transiently colonises root cells, producing hyphal structures called arbuscules. The movement of phosphate from fungus to plant is well established, however its coordination and regulation at the ephemeral arbuscules remains elusive. Here, non-invasive imaging captures the complete growth and collapse of the arbuscules in unprecedented resolution, revealing heterogeneity in arbuscule development. Tracking the dynamics of rice PHosphate Transporter 1;11 (OsPHT1;11/ PT11) as a proxy for symbiotic phosphate transport shows consistent localisation across diverse arbuscules. However, we uncover phosphate-responsive variability in PT11 abundance, representing an essential, cellular-level layer of nutrient regulation. Such plasticity in arbuscule phosphate uptake capacity evidences uncoupling of arbuscule presence and arbuscule function, thereby demonstrating that arbuscules are not identical units of nutrient exchange.