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    POLYGALACTURONASE45 cleaves pectin and links cell proliferation and morphogenesis to leaf curvature in Arabidopsis thaliana. Yang Yang,Anderson Charles T,Cao Jiashu The Plant journal : for cell and molecular biology Regulating plant architecture is a major goal in current breeding programs. Previous studies have increased our understanding of the genetic regulation of plant architecture, but it is also essential to understand how organ morphology is controlled at the cellular level. In the cell wall, pectin modification and degradation are required for organ morphogenesis, and these processes involve a series of pectin-modifying enzymes. Polygalacturonases are a major group of pectin-hydrolyzing enzymes that cleave pectin backbones and release oligogalacturonides. Polygalacturonase genes function in cell expansion and separation, and contribute to organ expansion, separation, and dehiscence in plants. However, whether and how they influence other cellular processes and organ morphogenesis are poorly understood. Here, we characterized the functions of Arabidopsis POLYGALACTURONASE45 (PG45) in organ morphogenesis using genetic, developmental, cell biological, and biochemical analyses. A heterologously expressed portion of PG45 cleaves pectic homogalacturonan in vitro, indicating that PG45 is a bona fide polygalacturonase. PG45 functions in leaf and flower structure, branch formation and organ growth. Undulation in pg45 knockout and PG45 overexpression leaves is accompanied by impaired adaxial-abaxial polarity, and loss of PG45 shortens the duration of cell proliferation in the adaxial epidermis of developing leaves. Abnormal leaf curvature is coupled with altered pectin metabolism and autogenous oligogalacturonide profiles in pg45 knockout and PG45 overexpression leaves. Together, these results highlight a previously underappreciated function for PGs in determining tissue polarity and regulating cell proliferation, and imply the existence of oligogalacturonide-based signaling pathways that modulate plant development. 10.1111/tpj.15308
    Defects in Cell Wall Differentiation of the Arabidopsis Mutant Is Dependent on Cyclin-Dependent Kinase CDK8. Schumacher Isabel,Ndinyanka Fabrice Tohnyui,Abdou Marie-Therese,Kuhn Benjamin M,Voxeur Aline,Herger Aline,Roffler Stefan,Bigler Laurent,Wicker Thomas,Ringli Christoph Cells Plant cells are encapsulated by cell walls whose properties largely determine cell growth. We have previously identified the mutant, which shows defects in seedling root and shoot development. is affected in the () and shows alterations in the structures of Rhamnogalacturonan I (RG I) and RG II, two rhamnose-containing pectins. The data presented here shows that root tissue of the mutant fails to properly differentiate the cell wall in cell corners and accumulates excessive amounts of callose, both of which likely alter the physical properties of cells. A () mutant was identified that alleviates the cell growth defects in . The cell wall differentiation defect is re-established in the mutant and callose accumulation is reduced compared to . The mutation is an allele of the (), which encodes a component of the mediator complex that influences processes central to plant growth and development. Together, the identification of the mutant suggests that changes in cell wall composition and turnover in the mutant have a significant impact on cell growth and reveals a function of CDK8 in cell wall architecture and composition. 10.3390/cells10030685
    Ride to cell wall: Arabidopsis XTH11, XTH29 and XTH33 exhibit different secretion pathways and responses to heat and drought stress. De Caroli Monica,Manno Elisa,Piro Gabriella,Lenucci Marcello S The Plant journal : for cell and molecular biology The xyloglucan endotransglucosylase/hydrolases (XTHs) are enzymes involved in cell wall assembly and growth regulation, cleaving and re-joining hemicellulose chains in the xyloglucan-cellulose network. Here, in a homologous system, we compare the secretion patterns of XTH11, XTH33 and XTH29, three members of the Arabidopsis thaliana XTH family, selected for the presence (XTH11, XTH33) or the absence (XTH29) of a signal peptide, and the presence of a transmembrane domain (XTH33). We show that XTH11 and XTH33 reached, respectively, the cell wall and plasma membrane through a conventional protein secretion (CPS) pathway, while XTH29 moves towards the apoplast following an unconventional protein secretion (UPS) mediated by exocyst-positive organelles (EXPOs). All XTHs share a common C-terminal functional domain (XET-C) that, for XTH29 and a restricted number of other XTHs (27, 28, 30), continues with an extra-terminal region (ETR) of 45 amino acids. We suggest that this region is necessary for the correct cell wall targeting of XTH29 as the ETR-truncated protein never reaches its final destination nor is recruited by EXPOs. Furthermore, RT-qPCR-analyses performed on 4-week-old Arabidopsis seedlings exposed to drought and heat stress, suggest a different involvement of the three XTHs in cell wall remodeling under abiotic stress, evidencing stress-, organ- and time-dependent variations in the expression levels. Significantly, XTH29, codifying for the only XTH following an UPS pathway, is highly up-regulated with respect to XTH11 and XTH33 codifying for CPS secreted proteins. 10.1111/tpj.15301