The Organization Pattern of Root Border-Like Cells of Arabidopsis Is Dependent on Cell Wall Homogalacturonan      

Abstract

Border-like cells are released by Arabidopsis (Arabidopsis thaliana) root tips as organized layers of several cells that remain attached to each other rather than completely detached from each other, as is usually observed in border cells of many species. Unlike border cells, cell attachment between border-like cells is maintained after their release into the external environment. To investigate the role of cell wall polysaccharides in the attachment and organization of border-like cells, we have examined their release in several well-characterized mutants defective in the biosynthesis of xyloglucan, cellulose, or pectin. Our data show that among all mutants examined, only quasimodo mutants (qua1-1 and qua2-1), which have been characterized as producing less homogalacturonan, had an altered border-like cell phenotype as compared with the wild type. Border-like cells in both lines were released as isolated cells separated from each other, with the phenotype being much more pronounced in qua1-1 than in qua2-1. Further analysis of border-like cells in the qua1-1 mutant using immunocytochemistry and a set of anti-cell wall polysaccharide antibodies showed that the loss of the wild-type phenotype was accompanied by (1) a reduction in homogalacturonan-JIM5 epitope in the cell wall of border-like cells, confirmed by Fourier transform infrared microspectrometry, and (2) the secretion of an abundant mucilage that is enriched in xylogalacturonan and arabinogalactan-protein epitopes, in which the cells are trapped in the vicinity of the root tip.

Root exudate ofSolanum tuberosumis enriched in galactose-containing molecules and impacts the growth ofPectobacterium atrosepticum

“…Although we show that galactancontaining polymers such as RGI are constituents of potato root exudates, AGPs appear to be the most abundant molecules. This observation is in agreement with previous findings reporting the presence of AGPs in quite high amounts in root exudates of various plant species (Moody et al, 1988;Durand et al, 2009;Ma et al, 2010;Cannesan et al, 2012). However, AGPs were not the only HRGPs represented in the root exudates of potato.…”

“…They were then sown onto Murashige and Skoog medium containing 3Á5 % (w/v) Bacto Agar supplemented with 3 % (w/v) sucrose (Durand et al, 2009). Plants were grown in a culture chamber under continuous light (120 mE m À2 s À1 ) for 18 h at 24 C and 6 h for 18 C. To prevent the roots penetrating the agar and the subsequent loss of border cells, plants were grown in vertically oriented Petri dishes.…”

“…Ruthenium red dye (Sigma) was used at 0Á05 % (w/v) in deionized water for 15 min. Roots were carefully washed in deionized water and observed using a bright-field microscope (Durand et al, 2009). To test viability, staining with 5 mM calcein acetoxymethyl ester (calcein-AM; Sigma) was performed as described in Vicré et al (2005).…”

“…Moreover, the nature of the polysaccharides and other glycan-containing molecules of root exudates plays a major role in mediating root-microbe interactions (Hinch and Clarke, 1980;Irving and Grant, 1984;Ray and Callow, 1988;Cannesan et al, 2012, Nguema-Ona et al, 2013. Although hydroxyproline has been reported to be a minor component in maize and cress exudates (Ray and Callow, 1988), glycoproteins such as arabinogalactan proteins (AGPs), which belong to the hydroxyproline-rich glycoprotein (HRGP) family, have been found to occur in root secretions of many plant species, such as pea, arabidopsis and Brassica napus (Knee et al, 2001;Durand et al, 2009;Cannesan et al, 2012).…”

“…This mucilage is mainly produced by root cap cells. It contains high amounts of polysaccharides, which confer sticky and gel-like properties (Durand et al, 2009). In addition, the mucilage also contains many lowmolecular-weight molecules, proteins and extracellular DNA (Wen et al, 2007(Wen et al, , 2009Cannesan et al, 2012;York et al, 2016).…”