Cell-to-cell movement of GFP during embryogenesis and early seedling development in Arabidopsis

Abstract

There is increasing evidence for intercellular trafficking of macromolecules through plasmodesmata (PD) during plant development. Here we study the ability of PD to traffic proteins during embryogenesis and early seedling development in Arabidopsis. Transgenic lines that induce GFP expression only in meristems, MSG (meristem-specific GFP), were used to monitor GFP movement. Cell-to-cell movement of different-sized GFP reporters reveals that embryos and young seedlings traffic proteins at least 54 kDa in size. Although 27-kDa soluble GFP (1؋sGFP) freely moves between cells throughout the entire embryo during all stages analyzed, 2؋sGFP movement becomes more restricted as development proceeds. After germination, cells near the apical meristem in seedlings show a higher size exclusion limit (SEL), whereas the SEL becomes more restricted as surrounding tissues develop identities. Although 1؋sGFP moves throughout leaf primordia, as the leaf develops only the basal part of leaf petioles, main vascular tissues, and leaf veins (not blades) allow 1؋sGFP movement. Although previous studies showed that embryos allow movement of small symplastic tracers (0.5 kDa), the present data demonstrate that the embryo constitutes a single symplast that allows transport of macromolecules as well. Even 2؋sGFP moves from its site of expression at the apical meristem in embryos and seedlings, yet the extent of movement is more limited than 1؋sGFP. Thus, PD have distinct SELs in different subregions of the embryo and seedling. These studies support the general concept that PD in younger tissues are more dilated and less restrictive than PD in older (nonvascular) tissues.plasmodesmata ͉ symplast

Subdomains for transport via plasmodesmata corresponding to the apical–basal axis are established during Arabidopsis embryogenesis

“…2 B and C, arrow). In a slightly later heart staged embryo (bigger in size without obvious hypocotyl elongation) (15), movement of 2ϫ sGFP begins to be limited in the area of the cotyledons so that 2ϫ sGFP shows a movement pattern similar to that shown for 3ϫ sGFP in Fig. 2D.…”

“…[Here we define the early heart stage as when embryos are clearly heart shaped, but are small, representing an earlier stage than the one analyzed in ref. 15 where movement of 2ϫ sGFP was limited]. The region defined by GUS activity is more extensive than ER-GFP expression (compare Fig.…”

“…Thus, the embryo is minimally affected by physiology and environment. PD in Arabidopsis embryos were first viewed ultrastructurally (12), and a few studies assessed PD function during embryogenesis (13)(14)(15).…”

Non-cell-autonomous rescue of anaphase-promoting complex function revealed by mosaic analysis of HOBBIT , an Arabidopsis CDC27 homolog

“…It is not likely a direct movement of the large HBT protein or the even larger APC͞C complex, because protein trafficking is limited by the plasmodesmatal size exclusion limit that has been estimated to be between 40 and 60 kDa for Arabidopsis embryos (41). Might other cell cycle regulators, produced in cycling HBT cells as a consequence of ongoing cell division, move to hbt 2311 neighboring cells?…”

Identification of an interactor of cadmium ion-induced glycine-rich protein involved in regulation of callose levels in plant vasculature

“…One of the important parameters describing the molecular permeability of plasmodesmata is the size exclusion limit, which sets the largest size of the molecules that can traffic through the plasmodesmata through passive transport. Plant cells in different tissues at different developmental stages are known to possess plasmodesmata with different size exclusion limit (6).…”