From plasmodesma geometry to effective symplasmic permeability through biophysical modelling.

Eva E Deinum,Yoselin Benitez-Alfonso,Bela M Mulder

doi:10.7554/elife.49000

Abstract

Regulation of molecular transport via intercellular channels called plasmodesmata (PDs) is important for both coordinating developmental and environmental responses among neighbouring cells, and isolating (groups of) cells to execute distinct programs. Cell-to-cell mobility of fluorescent molecules and PD dimensions (measured from electron micrographs) are both used as methods to predict PD transport capacity (i.e., effective symplasmic permeability), but often yield very different values. Here, we build a theoretical bridge between both experimental approaches by calculating the effective symplasmic permeability from a geometrical description of individual PDs and considering the flow towards them. We find that a dilated central region has the strongest impact in thick cell walls and that clustering of PDs into pit fields strongly reduces predicted permeabilities. Moreover, our open source multi-level model allows to predict PD dimensions matching measured permeabilities and add a functional interpretation to structural differences observed between PDs in different cell walls.

Highlights

The formation of spatial patterns in plants requires the transport and interaction of molecular signals
Our aim is to describe the symplasmic transport properties of a cell wall as an effective wall permeability, that is a single number that could be plugged into tissue/organ level models
We opted for a simple geometrical description that allows us to study the effects of PD neck, central region and desmotubule dimensions with as few parameters as possible

Summary

Introduction

The formation of spatial patterns in plants requires the transport and interaction of molecular signals. This sharing of information coordinates cell fate decisions over multiple cells and the isolation of cell fate determinants within a cell or group of cells on the same developmental path. Small molecules such as sugars, peptides, hormones and RNAs move long and short distances to coordinate cell/ organ development (Otero et al, 2016). Cell-to-cell transport of proteins, such as transcription factors, is important in the regulation and/or developmental reprogramming of local cellular domains (Gallagher et al, 2014). Other mobile factors with developmental importance include TARGET OF MONOPTEROS 7, PEAR transcription factors and miRNAs (Lu et al, 2018; Miyashima et al, 2019; Skopelitis et al, 2018)

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