Plants have intercellular channels, plasmodesmata (PD), that span the cell wall to enable cell-to-cell transport of micro-and macromolecules. We identified an Arabidopsis thaliana embryo lethal mutant increased size exclusion limit 1 (ise1) that results in increased PDmediated transport of fluorescent tracers. The ise1 mutants have a higher frequency of branched and twinned PD than wild-type embryos. Silencing of ISE1 in mature Nicotiana benthamiana leaves also leads to increased PD transport, as monitored by intercellular movement of a GFP fusion to the tobacco mosaic virus movement protein.ISE1 encodes a putative plant-specific DEAD-box RNA helicase that localizes specifically to mitochondria. The N-terminal 100 aa of ISE1 specify mitochondrial targeting. Mitochondrial metabolism is compromised severely in ise1 mutant embryos, because their mitochondrial proton gradient is disrupted and reactive oxygen species production is increased. Although mitochondria are essential for numerous cell-autonomous functions, the present studies demonstrate that mitochondrial function also regulates the critical cell non-cell-autonomous function of PD.intercellular ͉ traffic ͉ Arabidopsis ͉ embryogenesis ͉ Redox

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

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

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Endothelial