Spatiotemporal dynamics of anionic phospholipids orchestrate lateral root initiation and morphogenesis in <i>Arabidopsis thaliana</i>

Lateral root (LR) development in Arabidopsis thaliana requires precise coordination of pericycle founder cell (FC) specification, patterning, and morphogenesis. While auxin signalling is well established in this process, the role of membrane phospholipid signalling-particularly of phosphoinositides-remains less understood. Here, we investigate the contribution of the anionic phospholipids phosphatidylinositol 4-phosphate (PI4P), phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], and phosphatidylserine (PS) to LR formation using live-cell biosensors, genetic mutants, and inducible lipid depletion tools. We show that PI4P is uniformly distributed throughout lateral root primordia (LRPs), whereas PI(4,5)P2 is specifically depleted in the proliferative core during early LRP development. Time-lapse imaging revealed stable PI4P and PI(4,5)P2 levels before and after FC activation, while PS increased rapidly post-activation. In xylem-pole pericycle (XPP) cells, PI(4,5)P2 decreased and PS increased following LR initiation, with both changes occurring in a membrane domain-specific manner. Genetic analysis of the pip5k1pip5k2 double mutant, deficient in PI(4,5)P2 synthesis, revealed impaired LR initiation and emergence. Conversely, inducible depletion of PI(4,5)P2 using the iDePP system promoted FC specification and accelerated LRP morphogenesis. These results suggest that PI4P functions as a stable basal phospholipid, whereas PI(4,5)P2 and PS undergo dynamic, spatially regulated changes that are critical for LR development. Notably, PI(4,5)P2 acts as a negative regulator of LRP initiation and morphogenesis. Our findings highlight how phospholipid signalling, in coordination with hormonal cues, provides spatial and temporal control over pericycle cell behaviour and lateral root organogenesis.