Arabidopsis PIN2 protein directs transport of the phytohormone auxin from the root tip into the root elongation zone. Variation in hormone transport, which depends on a delicate interplay between PIN2 sorting to and from polar plasma membrane domains, determines root growth. By employing a constitutively degraded version of PIN2, we identify brassinolides as antagonists of PIN2 endocytosis. This response does not require de novo protein synthesis, but involves early events in canonical brassinolide signaling. Brassinolide-controlled adjustments in PIN2 sorting and intracellular distribution governs formation of a lateral PIN2 gradient in gravistimulated roots, coinciding with adjustments in auxin signaling and directional root growth. Strikingly, simulations indicate that PIN2 gradient formation is no prerequisite for root bending but rather dampens asymmetric auxin flow and signaling. Crosstalk between brassinolide signaling and endocytic PIN2 sorting, thus, appears essential for determining the rate of gravity-induced root curvature via attenuation of differential cell elongation.

• MeSH
• Arabidopsis účinky léků   metabolismus   MeSH
• biologický transport účinky léků   MeSH
• brassinosteroidy metabolismus   farmakologie   MeSH
• endocytóza účinky léků   MeSH
• gravitropismus účinky léků   fyziologie   MeSH
• kořeny rostlin účinky léků   metabolismus   MeSH
• kyseliny indoloctové metabolismus   MeSH
• meristém účinky léků   metabolismus   MeSH
• proteiny huseníčku metabolismus   MeSH
• regulátory růstu rostlin metabolismus   farmakologie   MeSH
• signální transdukce MeSH
• steroidy heterocyklické metabolismus   farmakologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• brassinolide MeSH Prohlížeč
• brassinosteroidy MeSH
• kyseliny indoloctové MeSH
• PIN2 protein, Arabidopsis MeSH Prohlížeč
• proteiny huseníčku MeSH
• regulátory růstu rostlin MeSH
• steroidy heterocyklické MeSH

The intercellular transport of auxin is driven by PIN-formed (PIN) auxin efflux carriers. PINs are localized at the plasma membrane (PM) and on constitutively recycling endomembrane vesicles. Therefore, PINs can mediate auxin transport either by direct translocation across the PM or by pumping auxin into secretory vesicles (SVs), leading to its secretory release upon fusion with the PM. Which of these two mechanisms dominates is a matter of debate. Here, we addressed the issue with a mathematical modeling approach. We demonstrate that the efficiency of secretory transport depends on SV size, half-life of PINs on the PM, pH, exocytosis frequency and PIN density. 3D structured illumination microscopy (SIM) was used to determine PIN density on the PM. Combining this data with published values of the other parameters, we show that the transport activity of PINs in SVs would have to be at least 1000× greater than on the PM in order to produce a comparable macroscopic auxin transport. If both transport mechanisms operated simultaneously and PINs were equally active on SVs and PM, the contribution of secretion to the total auxin flux would be negligible. In conclusion, while secretory vesicle-mediated transport of auxin is an intriguing and theoretically possible model, it is unlikely to be a major mechanism of auxin transport in planta.

• Klíčová slova
• 3D-SIM microscopy, PIN transporters, auxin, mathematical modeling, polar auxin transport, secretion,
• MeSH
• Arabidopsis metabolismus   MeSH
• biologické modely * MeSH
• biologický transport MeSH
• endocytóza MeSH
• kyseliny indoloctové metabolismus   MeSH
• permeabilita buněčné membrány MeSH
• proteiny huseníčku metabolismus   MeSH
• sekreční vezikuly metabolismus   MeSH
• zelené fluorescenční proteiny metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• kyseliny indoloctové MeSH
• proteiny huseníčku MeSH
• zelené fluorescenční proteiny MeSH

The phytohormone auxin is the information carrier in a plethora of developmental and physiological processes in plants1. It has been firmly established that canonical, nuclear auxin signalling acts through regulation of gene transcription2. Here, we combined microfluidics, live imaging, genetic engineering and computational modelling to reanalyse the classical case of root growth inhibition3 by auxin. We show that Arabidopsis roots react to addition and removal of auxin by extremely rapid adaptation of growth rate. This process requires intracellular auxin perception but not transcriptional reprogramming. The formation of the canonical TIR1/AFB-Aux/IAA co-receptor complex is required for the growth regulation, hinting to a novel, non-transcriptional branch of this signalling pathway. Our results challenge the current understanding of root growth regulation by auxin and suggest another, presumably non-transcriptional, signalling output of the canonical auxin pathway.

• MeSH
• Arabidopsis růst a vývoj   metabolismus   MeSH
• F-box proteiny metabolismus   MeSH
• gravitropismus MeSH
• kořeny rostlin růst a vývoj   metabolismus   MeSH
• kyseliny indoloctové metabolismus   MeSH
• proteiny huseníčku metabolismus   MeSH
• receptory buněčného povrchu metabolismus   MeSH
• regulátory růstu rostlin metabolismus   MeSH
• signální transdukce * MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• F-box proteiny MeSH
• indoleacetic acid MeSH Prohlížeč
• kyseliny indoloctové MeSH
• proteiny huseníčku MeSH
• receptory buněčného povrchu MeSH
• regulátory růstu rostlin MeSH
• TIR1 protein, Arabidopsis MeSH Prohlížeč