Cell surface auxin signalling directly targets PIN-mediated auxin fluxes for adaptive plant development

Abstract

The plant hormone auxin and its directional transport across tissues mediate much of the remarkably adaptive and plastic development of higher plants. Positive feedback between auxin signalling and transport is a key prerequisite for self-organizing development including flexible vascular tissue formation and directional growth responses, such as gravitropism. Here we identified a mechanistic link between cell surface ABP1-based auxin perception, the associated TMK1 kinase and PIN auxin transporters. abp1 and tmk1 mutants are defective in auxin-triggered phosphorylation of PIN proteins and in PIN-mediated directional auxin transport. Auxin, via ABP1, induces activation and stabilization of TMK1, thus promoting direct interaction with and phosphorylation of PIN2. Following gravistimulation, the auxin-activated TMK1 acts along the lower root side to reinforce asymmetry in PIN2-mediated auxin fluxes for gravitropic root bending. This ABP1-TMK1-dependent positive feedback on PIN-mediated directional auxin transport is fundamental for robust root gravitropism and presumably also for other self-organizing developmental processes.

How plants cope with fast primary root elongation inhibition

“…However, the loss-of-function abp1 mutant responds normally to auxin in fast primary root elongation inhibition ( Li et al., 2021 ). Nonetheless, further analysis of abp1 tmk1 double mutant in the fast auxin response is further needed ( Rodriguez et al., 2022 ). Collectively, the TIR1/AFB and cell surface TMK1 kinase mediate antagonistic auxin signaling to fine-tune primary root elongation rapidly, but the mechanisms are still beyond our current understanding ( Figure 1 ).…”