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Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle.

Published version
Peer-reviewed

Type

Article

Change log

Authors

Ross-Elliott, TJ 
Jensen, KH 
Haaning, KS 
Wager, BM 
Knoblauch, J 

Abstract

In plants, a complex mixture of solutes and macromolecules is transported by the phloem. Here, we examined how solutes and macromolecules are separated when they exit the phloem during the unloading process. We used a combination of approaches (non-invasive imaging, 3D-electron microscopy, and mathematical modelling) to show that phloem unloading of solutes in Arabidopsis roots occurs through plasmodesmata by a combination of mass flow and diffusion (convective phloem unloading). During unloading, solutes and proteins are diverted into the phloem-pole pericycle, a tissue connected to the protophloem by a unique class of ‘funnel plasmodesmata’. While solutes are unloaded without restriction, large proteins are released through funnel plasmodesmata in discrete pulses, a phenomenon we refer to as ‘batch unloading’. Unlike solutes, these proteins remain restricted to the phloem-pole pericycle. Our data demonstrate a major role for the phloem-pole pericycle in regulating phloem unloading in roots.

Description

Keywords

plant biology, $\textit{A. thaliana}$, funnel plasmodesmata, long distance signaling, phloem, phloem pole pericycle, phloem unloading, protophloem

Journal Title

eLife

Conference Name

Journal ISSN

2050-084X
2050-084X

Volume Title

6

Publisher

eLife Sciences Publications
Sponsorship
KJO acknowledges the financial support of the BBSRC. We thank Ilya Belevich for preparing material for SBFSEM and Kirsten Knox and Andrea Paterlini for advice on tracer experiments. We thank Pawel Roszak for providing T2 seeds of psAPL::icals3m lines. We thank the Francheschi Microscopy and Imaging center for technical support. This work was supported by National Science Foundation grant IOS-1146500 (MK).