Cytoskeleton dynamics control early events of lateral root initiation in Arabidopsis

SUMMARY How plant cells re-establish differential growth to initiate organs is poorly understood. Morphogenesis of lateral roots relies on the tightly controlled radial expansion and asymmetric division of founder cells. The cellular mechanisms that license and ensure these features are unknown. Here, we quantitatively analyse F-actin and microtubule dynamics during LR initiation. Using mutants, pharmacological and tissue-specific genetic perturbations, we show that dynamic reorganisation of both microtubule and F-actin networks is required for the asymmetric expansion of the founder cells. This cytoskeleton remodelling intertwine with auxin signalling in the pericycle and endodermis in order for founder cells to acquire a basic polarity required for initiating LR development. Our results reveal the conservation of cell remodelling and polarisation strategies between the Arabidopsis zygote and lateral root founder cells. We propose that coordinated, auxin-driven reorganisation of the cytoskeleton licenses asymmetric cell growth and divisions during embryonic and post-embryonic organogenesis. HIGHLIGHTS Failure for lateral root founder cells to undergo asymmetric radial expansion before division, leads to aberrant organ formation. Cortical microtubules arrays reorganise to facilitate this asymmetric expansion and F-actin the asymmetric division. Cytoskeletal reorganisation depends on auxin signalling. New genetic tools allow to perturb microtubules or actin in an inducible and cell-type specific manner.