Cell Wall Biosynthesis
The cell wall is a defining feature of plants. The wall affects all aspects of a plant's growth, development, morphology, and response to the environment. Plant cell walls consist largely of cellulose microfibrils embedded in a matrix of lignin, hemicellulose, pectins, and protein. Whereas the structure of cellulose is similar in all plants and tissues, the hemicelluloses are more heterogeneous and differ in structure and sugar composition among species and tissues.
Plant cell walls have major impacts on human affairs. Plant cell walls are an important ecological component of all ecosystems. Plant cell walls provide fuel, fiber, and food for human use.
The CSL genes of rice
The structure of cereal cell walls. Cereals, including rice, maize, wheat, millet, sorghum, rye, and barley, are the major food source for humans. Cereal stover (crop debris), composed mainly of cell walls, represents a huge resource for the production of renewable energy.
The primary walls of grasses (family Poaceae) are distinct not just from those of dicotyledenous plants but even from those of other monocotyledons. The major hemicellulosic component of the primary walls of grass seedlings is glucuronoarabinoxylan (GAX), composed of a beta-1,4-D-xylan backbone substituted with terminal alpha-L-arabinofuranose and alpha-D-glucuronic acid.
Cereals also contain a hemicellulose known as mixed-linked glucan (MLG), a linear glucan containing both beta-1,3- and beta-1,4- linkages.
Cereals also contain significant levels of xyloglucan (Hayashi, 1989, Annu. Rev. Plant Physiol. 40:139). The structure of cereal xyloglucan differs from that of dicots in being less substituted. Whereas in dicot xyloglucan almost every glucose molecule is substituted with xylose and/or galactose and fucose, the xyloglucan of cereals is sparsely substituted with only xylose. One effect of a lower level of substitution is decreased solubility in water.
The CESA and CSL genes. The CESA genes encode cellulose synthases. Plants also contain a large number of genes that are related to the CESA genes. These "cellulose synthase-like" (CSL) genes have been found in all plants and those from Arabidopsis have been classified into six sub-families.
The CSL genes of rice. We analyzed the available CSL and CESA genes from cereals, including rice, maize, sorghum, and wheat. We have concluded that there are 9 (maybe 10) CESA genes and 34 CSL genes in rice. See Hazen et al. (2002).