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

Abstract

The axial body pattern of Arabidopsis is determined during embryogenesis by auxin signaling and differential gene expression. Here we demonstrate that another pathway, cell-to-cell communication through plasmodesmata (PD), is regulated during apicalbasal pattern formation. The SHOOT MERISTEMLESS (STM) promoter was used to drive expression in the shoot apical meristem (SAM) and a subset of cells at the base of the hypocotyl of 1؋, 2؋, and 3؋ soluble green fluorescent proteins (sGFPs), and the P30 movement protein of Tobacco mosaic virus (TMV) translationally fused to 1؋ and 2؋ sGFP. In the early heart stage, 2؋ sGFP (54 kDa) moves throughout the whole embryo, whereas 3؋ sGFP (81 kDa) shows more restricted movement. As the embryo develops, PD apertures are down regulated to form local subdomains allowing transport of different sized tracers. For example, movement of 2؋ sGFP to the cotyledon, and 3؋ sGFP to root tips, becomes restricted. Subdomains of cell-to-cell transport align with the apical-basal embryo body axis and correspond to the shoot apex, cotyledons, hypocotyl, and root. Studies with P30 -GFP fusions reinforce the distinction between embryonic symplastic subdomains. Although P30 targets embryo cell walls as puncta (diagnostic for functional localization of P30 to PD in adult plants), P30 cannot dilate embryonic PD to overcome the barriers for transport between symplastic subdomains, suggesting that specific boundaries separate symplastic subdomains of the embryo. Thus, cell-to-cell communication via plasmodesmata conveys positional information critical to establish the axial body pattern during embryogenesis in Arabidopsis.GFP ͉ symplast ͉ Tobacco mosaic virus movement protein P30 ͉ STM

SUPERMAN prevents class B gene expression and promotes stem cell termination in the fourth whorl of Arabidopsis thaliana flowers

“…Whether such a repression is direct or indirect, however, remains unknown. Conversely, SUP affects floral stem cells noncell-autonomously [the fully complementing gSUP-3xVenusN7 construct encodes a protein that exceeds the size exclusion limit for passage through plasmodesmata (30), showing that the SUP protein does not need to migrate from cell to cell to accomplish its function], and independently of AG expression (Fig. 4).…”

Transcriptional and posttranscriptional regulation of transcription factor expression in Arabidopsis roots

“…Our results are not consistent with a passive process based on three observations. First, for passively moving proteins, smaller proteins were shown to move more effectively than larger ones, presumably dependent on the size exclusion limits of plasmodesmata (30). Here, the size distribution of moving and nonmoving TFs overlapped.…”

Coordination of apical and basal embryo development revealed by tissue-specific GNOM functions

“…Kim et al (Kim et al, 2005), for example, described size restrictions for proteins to move within embryonic tissues. Being much larger than 3ϫGFP whose cell-to-cell movement was very limited, GNOM should be restricted to the cells of expression.…”