Cell Wall Modifications in Arabidopsis Plants with Altered α-l-Arabinofuranosidase Activity  

Abstract

Although cell wall remodeling is an essential feature of plant growth and development, the underlying molecular mechanisms are poorly understood. This work describes the characterization of Arabidopsis (Arabidopsis thaliana) plants with altered expression of ARAF1, a bifunctional a-L-arabinofuranosidase/b-D-xylosidase (At3g10740) belonging to family 51 glycosyl-hydrolases. ARAF1 was localized in several cell types in the vascular system of roots and stems, including xylem vessels and parenchyma cells surrounding the vessels, the cambium, and the phloem. araf1 T-DNA insertional mutants showed no visible phenotype, whereas transgenic plants that overexpressed ARAF1 exhibited a delay in inflorescence emergence and altered stem architecture. Although global monosaccharide analysis indicated only slight differences in cell wall composition in both mutant and overexpressing lines, immunolocalization experiments using anti-arabinan (LM6) and anti-xylan (LM10) antibodies indicated cell type-specific alterations in cell wall structure. In araf1 mutants, an increase in LM6 signal intensity was observed in the phloem, cambium, and xylem parenchyma in stems and roots, largely coinciding with ARAF1 expression sites. The ectopic overexpression of ARAF1 resulted in an increase in LM10 labeling in the secondary walls of interfascicular fibers and xylem vessels. The combined ARAF1 gene expression and immunolocalization studies suggest that arabinan-containing pectins are potential in vivo substrates of ARAF1 in Arabidopsis.Cell walls undergo dynamic changes during plant growth and development. Wall composition and macromolecular assembly vary greatly among taxa, species, organs, and cell types within an individual or domains of a given cell wall. These differences contribute to cell shape and, in some cases, specialized cellular function. Cell wall-related genomic approaches in different physiological contexts have revealed that many cell wall biosynthetic/modifying enzymes and structural proteins are regulated at the transcriptional level. In the case of secondary wall formation, one can correlate morphological and cytological cellular changes with the spatial and temporal regulation of wall-modifying enzymes over a developmental xylem gradient in poplar (Populus spp.;Schrader et al., 2004) and in in vitro tracheary elements (TEs) of zinnia (Zinnia elegans;Milioni et al., 2001;Demura et al., 2002;Pesquet et al., 2005). In a genomic approach of zinnia TEs, Pesquet et al. (2005) identified a family 51 (Carbohydrate Active enZYmes [CAZY] database, http://www.cazy.org; Coutinho and Henrissat, 1999) a-L-arabinofuranosidase (arabinofuranosidase) that was highly expressed in TE induction medium at the onset of secondary wall formation. Interestingly, although relatively little redundancy was observed in sequence data generated from the different genomic studies in zinnia, this family 51 arabinofuranosidase gene was systematically identified. At3g10740 is the closest Arabidopsis (Arabidopsis thaliana) homolog to the arabinofuranosidase...

AtBXL1 Encodes a Bifunctional β-d-Xylosidase/α-l-Arabinofuranosidase Required for Pectic Arabinan Modification in Arabidopsis Mucilage Secretory Cells

“…Bars = 500 mm. Montes et al, 2008). Our results complement and extend these data by demonstrating that the loss of arabinan modification in a specific cell type can lead to observable consequences on cell and plant developmental behavior: namely, the lack of cell wall breakage to facilitate mucilage release and consequent delayed seed hydration and germination.…”

Flowering as the Most Highly Sensitive Period of Grapevine (Vitis vinifera L. cv Mourvèdre) to the Botryosphaeria Dieback Agents Neofusicoccum parvum and Diplodia seriata Infection

“…Additional studies on UDP-Glc DH indicate that the oxidation of UDP-Glc may have a significant role in increasing the pool of UDP-sugars to supply the demand for increased matrix polysaccharide and cellulose synthesis of structural polysaccharides in plants [42,43]. Moreover, accumulation of GDP-mannose 3,5 epimerase (s6426) and beta-xylosidase/alpha- l -arabinofurasidase (s6626) in stems infected by Np confirmed the activation of cell-wall biosynthesis/modification [44,45,46]. …”

Walls are thin 1 (WAT1), an Arabidopsis homolog of Medicago truncatula NODULIN21, is a tonoplast-localized protein required for secondary wall formation in fibers

“…For LM10 immunohistochemistry, samples were treated and observed as previously described (Chávez Montes et al. , 2008).…”