Root twisting drives halotropism via stress-induced microtubule reorientation

Plants have evolved signaling mechanisms that guide growth away from adverse environments that can cause yield losses. Root halotropism is a sodium-specific negative tropism that is crucial for surviving and thriving under high salinity. Although root halotropism was discovered some years ago, the underlying mo-lecular and cellular mechanisms remain unknown. Here, we show that abscisic acid (ABA)-mediated root twisting determines halotropism in Arabidopsis. An ABA-activated SnRK2 protein kinase (SnRK2.6) phos-phorylates the microtubule-associated protein SP2L at Ser406, which induces a change in the anisotropic cell expansion at the root transition zone and is required for root twisting during halotropism. Salt stress trig-gers SP2L-mediated cortical microtubule reorientation, which guides cellulose microfibril patterns. Our find-ings thus outline the molecular mechanism of root halotropism and indicate that anisotropic cell expansion through microtubule reorientation and microfibril deposition has a central role in mediating tropic responses.

Automated summary

This study reveals that ABA-mediated root twisting determines the mechanism of plant root halotropism, guiding anisotropic cell expansion through microtubule reorientation and cellulose microfibril deposition for plant growth in adverse environments.