Strigolactones, first discovered as germination stimulants for parasitic weeds , are carotenoid-derived phytohormones that play major roles in inhibiting lateral bud outgrowth and promoting plant-mycorrhizal symbiosis [2-4]. Furthermore, strigolactones are involved in the regulation of lateral and adventitious root development, root cell division [5, 6], secondary growth , and leaf senescence . Recently, we discovered the strigolactone transporter Petunia axillaris PLEIOTROPIC DRUG RESISTANCE 1 (PaPDR1), which is required for efficient mycorrhizal colonization and inhibition of lateral bud outgrowth . However, how strigolactones are transported through the plant remained unknown. Here we show that PaPDR1 exhibits a cell-type-specific asymmetric localization in different root tissues. In root tips, PaPDR1 is co-expressed with the strigolactone biosynthetic gene DAD1 (CCD8), and it is localized at the apical membrane of root hypodermal cells, presumably mediating the shootward transport of strigolactone. Above the root tip, in the hypodermal passage cells that form gates for the entry of mycorrhizal fungi, PaPDR1 is present in the outer-lateral membrane, compatible with its postulated function as strigolactone exporter from root to soil. Transport studies are in line with our localization studies since (1) a papdr1 mutant displays impaired transport of strigolactones out of the root tip to the shoot as well as into the rhizosphere and (2) DAD1 expression and PIN1/PIN2 levels change in plants deregulated for PDR1 expression, suggestive of variations in endogenous strigolactone contents. In conclusion, our results indicate that the polar localizations of PaPDR1 mediate directional shootward strigolactone transport as well as localized exudation into the soil.
This work was funded by a grant of the Swiss National Foundation to E.M. We thank Dr. José María Mateos (University of Zurich) for providing us with the vibratome, Prof. Dolf Weijers (Wageningen University, the Netherlands) for shipping us his set of ligation-independent cloning vectors, Prof. Bruno Humbel (University of Lausanne) for suggestions on GFP-PDR1 detection, and Dr. Undine Krügel (University of Zurich) and Prof. Michal Jasinski (Polish Academy of Science) for hints on protein quantification.
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Sasse J, Simon S, Gübeli C, et al. Asymmetric localizations of the ABC transporter PaPDR1 trace paths of directional strigolactone transport. Current Biology. 2015;25(5):647-655. doi:10.1016/j.cub.2015.01.015
Sasse, J., Simon, S., Gübeli, C., Liu, G., Cheng, X., Friml, J., … Borghi, L. (2015). Asymmetric localizations of the ABC transporter PaPDR1 trace paths of directional strigolactone transport. Current Biology. Cell Press. https://doi.org/10.1016/j.cub.2015.01.015
Sasse, Joëlle, Sibu Simon, Christian Gübeli, Guowei Liu, Xi Cheng, Jiří Friml, Harro Bouwmeester, Enrico Martinoia, and Lorenzo Borghi. “Asymmetric Localizations of the ABC Transporter PaPDR1 Trace Paths of Directional Strigolactone Transport.” Current Biology. Cell Press, 2015. https://doi.org/10.1016/j.cub.2015.01.015.
J. Sasse et al., “Asymmetric localizations of the ABC transporter PaPDR1 trace paths of directional strigolactone transport,” Current Biology, vol. 25, no. 5. Cell Press, pp. 647–655, 2015.
Sasse J, Simon S, Gübeli C, Liu G, Cheng X, Friml J, Bouwmeester H, Martinoia E, Borghi L. 2015. Asymmetric localizations of the ABC transporter PaPDR1 trace paths of directional strigolactone transport. Current Biology. 25(5), 647–655.
Sasse, Joëlle, et al. “Asymmetric Localizations of the ABC Transporter PaPDR1 Trace Paths of Directional Strigolactone Transport.” Current Biology, vol. 25, no. 5, Cell Press, 2015, pp. 647–55, doi:10.1016/j.cub.2015.01.015.