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Abstract
Grasses and related commelinid monocot species synthesize cell walls distinct in composition from other angiosperm species. With few exceptions, the genomes of all angiosperms contain the genes that encode the enzymes for synthesis of all cell-wall polysaccharide, phenylpropanoid, and protein constituents known in vascular plants. RNA-seq analysis of transcripts expressed during development of the upper and lower internodes of maize (Zea mays) stem captured the expression of cell-wall-related genes associated with primary or secondary wall formation. High levels of transcript abundances were not confined to genes associated with the distinct walls of grasses but also of those associated with xyloglucan and pectin synthesis. Combined with proteomics data to confirm that expressed genes are translated, we propose that the distinctive cell-wall composition of grasses results from sorting downstream from their sites of synthesis in the Golgi apparatus and hydrolysis of the uncharacteristic polysaccharides and not from differential expression of synthases of grass-specific polysaccharides.
Highlights
The primary walls of all angiosperms are assembled from scaffolds of cellulose microfibrils interlaced with hemicellulosic xyloglucans (XyGs),xylans (GAXs), andmannans (Scheller and Ulvskov, 2010), and embedded in an independent but coextensive matrix of pectic polysaccharides (McCann and Roberts, 1991; Caffall and Mohnen, 2009)
We summarized the expression behaviors of families and subgroups of families associated with specific polysaccharides, denoting the genes expressed during stages of primary wall formation, transitional, and secondary wall formation (Table 1)
We found that maize CesA1 through CesA9 and their paralogs were associated with elongation and primary wall synthesis stages of development, and CesA10 through CesA12 and their paralogs were associated with secondary wall formation (Figure 3A; Table S1)
Summary
The primary walls of all angiosperms are assembled from scaffolds of cellulose microfibrils interlaced with hemicellulosic xyloglucans (XyGs), (glucuronoarabino)xylans (GAXs), and (gluco)mannans (Scheller and Ulvskov, 2010), and embedded in an independent but coextensive matrix of pectic polysaccharides (McCann and Roberts, 1991; Caffall and Mohnen, 2009). Type I walls incorporate predominantly Hyp- and Gly-rich structural proteins at the end of growth to reinforce the wall into final shape, whereas this reinforcement is supplied by a phenylpropanoid network in the type II wall (Carpita, 1996). This distinction results in strong autofluorescence in the primary wall in addition to that seen in vascular tissue (Rudall and Caddick, 1994). During vascular development and the formation of a thickened rind of the stem, cellulose, Cell Wall Genes of Grassses glucuronoxylans (GXs), and GAX become embedded in lignin (Carpita, 1996)
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