Elongating maize root: zone-specific combinations of polysaccharides from type I and type II primary cell walls

Abstract

the dynamics of cell wall polysaccharides may modulate the cell wall mechanics and thus control the expansion growth of plant cells. the unique composition of type ii primary cell wall characteristic of grasses suggests that they employ specific mechanisms for cell enlargement. We characterized the transcriptomes in five zones along maize root, clustered the expression of genes for numerous glycosyltransferases and performed extensive immunohistochemical analysis to relate the changes in cell wall polysaccharides to critical stages of cell development in Poaceae. Specific patterns of cell wall formation differentiate the initiation, realization and cessation of elongation growth. Cell walls of meristem and early elongation zone represent a mixture of type I and type II specific polysaccharides. Xyloglucans and homogalacturonans are synthesized there actively together with mixed-linkage glucans and glucuronoarabinoxylans. Rhamnogalacturonans-I with the side-chains of branched 1,4-galactan and arabinan persisted in cell walls throughout the development. Thus, the machinery to generate the type I primary cell wall constituents is completely established and operates. The expression of glycosyltransferases responsible for mixed-linkage glucan and glucuronoarabinoxylan synthesis peaks at active or late elongation. These findings widen the number of jigsaw pieces which should be put together to solve the puzzle of grass cell growth. The ability to expand or to elongate many times compared to the initial size is a vital property of plant cells. Cells which are capable to grow are surrounded by a thin primary cell wall (PCW). The enlargement of plant cells occurs under the action of turgor pressure and is controlled by the mechanical properties of their cell walls. Mechanical properties, in turn, depend on the cell wall composition and architecture. The mechanisms underlying the growth of plant cells have mainly been studied in dicotyledonous species and non-commelinoid monocots with type I primary cell walls (Fig. 1). Cellulose in the form of microfibrils is present in plant cell walls of all types. Type I cell walls also have pectins and xyloglucans (XyGs) as the basic constituents 1. Hydrated pectin matrix fills the spaces between cellulose microfibrils. The major part of XyGs also exists between microfibrils in a coiled conformation or interacts with them in an extended conformation. However, minor portion of XyGs is entrapped between cellulose strands 2. These local interactions of XyGs with cellulose named "biomechanical hotspots" were proposed to form microfibril junctions and integrate them into one load-bearing network 3. The modification of these junctions by α-expansins enables the irreversible microfibril movements required for cell wall expansion 2. Alterations in the pectin structure are also considered a potential mechanism regulating wall expansion. Changes in cell wall hydration, the degree of cross-linking or accessibility of individual molecules to degrading enzymes are supposed to be a mechanism underl...

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Forgotten Actors: Glycoside Hydrolases During Elongation Growth of Maize Primary Root

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