F-Actin-Dependent Endocytosis of Cell Wall Pectins in Meristematic Root Cells. Insights from Brefeldin A-Induced Compartments

Abstract

(D.W.M.) Brefeldin A (BFA) inhibits exocytosis but allows endocytosis, making it a valuable agent to identify molecules that recycle at cell peripheries. In plants, formation of large intracellular compartments in response to BFA treatment is a unique feature of some, but not all, cells. Here, we have analyzed assembly and distribution of BFA compartments in development-and tissue-specific contexts of growing maize (Zea mays) root apices. Surprisingly, these unique compartments formed only in meristematic cells of the root body. On the other hand, BFA compartments were absent from secretory cells of root cap periphery, metaxylem cells, and most elongating cells, all of which are active in exocytosis. We report that cell wall pectin epitopes counting rhamnogalacturonan II dimers cross-linked by borate diol diester, partially esterified (up to 40%) homogalacturonan pectins, and (134)-␤-d-galactan side chains of rhamnogalacturonan I were internalized into BFA compartments. In contrast, Golgi-derived secretory (esterified up to 80%) homogalacturonan pectins localized to the cytoplasm in control cells and did not accumulate within characteristic BFA compartments. Latrunculin B-mediated depolymerization of F-actin inhibited internalization and accumulation of cell wall pectins within intracellular BFA compartments. Importantly, cold treatment and protoplasting prevented internalization of wall pectins into root cells upon BFA treatment. These observations suggest that cell wall pectins of meristematic maize root cells undergo rapid endocytosis in an F-actin-dependent manner.Eukaryotic cells perform endomembrane flow accomplished by vesicles shuttling among endoplasmic reticulum (ER), Golgi apparatus (GA), the plasma membrane (PM), and endosomes (for plants see Robinson et al., 1998; Hawes et al., 1999). These compartments and pathways of endomembrane flow are highly conserved in unicellular yeast, higher plants, and animals (for plant cells, see Robinson et al., 1998; Hawes et al., 1999). A major breakthrough in our current understanding of this complex endomembrane flow was provided by rediscovery of the fungal metabolite brefeldin A (BFA; Fujiwara et al., 1988). BFA action prevents vesicle formation in the exocytosis pathway by stabilizing abortive complexes between conserved ADP ribosylation factor 1 (ARF1) and the Sec7 domain of its guanine nucleotide exchange factor during the assembly of coat protein complexes of budding vesicles (for plants see, Pimpl et al., 2000;Robineau et al., 2000). Because of this action, BFA inhibits anterograde vesicular pathways while allowing endocytosis and some retrograde pathways to proceed further (Miller et al., 1992; Gaynor et al., 1998; Belanger and Quatrano, 2000). Moreover, BFA inhibits the endosome to vacuole transport in budding yeast (Gaynor et al., 1998).The introduction of BFA to investigate the cell biology of endomembrane flow in plant cells occurred some years later (Satiat-Jeunemaitre and Hawes, 1992), but most of the major findings concerning the effects of...

Arabidopsis MPK6 is involved in cell division plane control during early root development, and localizes to the pre-prophase band, phragmoplast, trans-Golgi network and plasma membrane

“…Double labelling of MPK6 and SCAMP1 clearly revealed their pronounced co-localization at TGN (Figure 9j-o, arrowheads). In order to localize Golgi we have used a commercial mouse monoclonal antibody 58 k. This antibody was previously shown to selectively label Golgi in lily pollen and maize root cells (Li and Yan, 2000;Baluška et al, 2002). As shown in Figure 9p-u, epidermal cells showed dispersed Golgi stacks within the cytoplasm.…”

Local Turgor Pressure Reduction via Channel Clustering

“…Endocytosis in plants has some parallels to the process in yeast, in particular its polymerized-actin dependence (42,43). The difficulties of overcoming high turgor pressure in plants by an actindependent process might thus be eased by a local turgor pressure reduction mechanism like that we discuss here for yeast.…”

Identification of Galacturonic Acid-1-phosphate Kinase, a New Member of the GHMP Kinase Superfamily in Plants, and Comparison with Galactose-1-phosphate Kinase

“…Although no plasmamembrane-localized transporters that import GalA into the cytosol have been identified, a large gene family with over 50 monosaccharide transporter-like genes exist in Arabidopsis (34), perhaps one of them is GalA transporter. Baluska et al (35) have suggested that the pectic fragment can be endocytosed. Previous studies indicate that exogalacturonates are present in the cytosol of pollen (36).…”