Functional Genomic Analysis Supports Conservation of Function Among Cellulose Synthase-Like A Gene Family Members and Suggests Diverse Roles of Mannans in Plants

Abstract

Mannan polysaccharides are widespread among plants, where they serve as structural elements in cell walls, as carbohydrate reserves, and potentially perform other important functions. Previous work has demonstrated that members of the cellulose synthase-like A (CslA) family of glycosyltransferases from Arabidopsis (Arabidopsis thaliana), guar (Cyamopsis tetragonolobus), and Populus trichocarpa catalyze b-1,4-mannan and glucomannan synthase reactions in vitro. Mannan polysaccharides and homologs of CslA genes appear to be present in all lineages of land plants analyzed to date. In many plants, the CslA genes are members of extended multigene families; however, it is not known whether all CslA proteins are glucomannan synthases. CslA proteins from diverse land plant species, including representatives of the mono-and dicotyledonous angiosperms, gymno-sperms, and bryophytes, were produced in insect cells, and each CslA protein catalyzed mannan and glucomannan synthase reactions in vitro. Microarray mining and quantitative real-time reverse transcription-polymerase chain reaction analysis demonstrated that transcripts of Arabidopsis and loblolly pine (Pinus taeda) CslA genes display tissue-specific expression patterns in vegetative and floral tissues. Glycan microarray analysis of Arabidopsis indicated that mannans are present throughout the plant and are especially abundant in flowers, siliques, and stems. Mannans are also present in chloronemal and caulonemal filaments of Physcomitrella patens, where they are prevalent at cell junctions and in buds. Taken together, these results demonstrate that members of the CslA gene family from diverse plant species encode glucomannan synthases and support the hypothesis that mannans function in metabolic networks devoted to other cellular processes in addition to cell wall structure and carbohydrate storage. Plant cells are enveloped by an extracellular matrix consisting of a highly organized and complex arrangement of carbohydrates, proteins, and often lignin. Among the many functions of plant cell walls, they define plant cell and organ shape, act as a barrier against plant pathogens, provide signals that direct growth and development, and supply strength and flexibility that enable plants to grow and respond to variable environmental conditions (Freshour et al., 2003; Somerville et al., 2004). Cellulose, pectins, and cross-linking glycans, including xyloglucans, xylans, mixed-linkage b-glucans, and mannans are the main constituents of plant cell walls. Variations in cell wall composition and architecture impart unique forms and functions to the variety of specialized cell types found in plants. Human uses of plant cell wall constituents are significant and wide ranging; plant cell walls are used as food, fuel, textiles and building materials. Whereas cell wall composition has been examined in a variety of plant species, only a small proportion of the hundreds of proteins predicted to be involved in cell wall biosynthesis and metabolism have been identified and characterized...

Pattern of Deposition of Cell Wall Polysaccharides and Transcript Abundance of Related Cell Wall Synthesis Genes during Differentiation in Barley Endosperm

“…Later in development heteromannan is present in the starchy endosperm but completely absent from aleurone cell walls. Experiments in which a number of CSLA genes from various plant species have been individually expressed heterologously in either plant or insect systems have shown that these genes encode (gluco)mannan synthases (Dhugga et al, 2004;Liepman et al, 2005Liepman et al, , 2007Suzuki et al, 2006;Doblin et al, 2010). However, this activity has not yet been demonstrated for any members of the cereal-specific clade of the CSLA family (van Erp and Walton, 2009).…”

“…The CslA genes from a broad range of species including Arabidopsis, guar (Cyamopsis tetragonoloba), poplar (Populus trichocarpa), loblolly pine (Pinus taeda), moss (Physcomitrella patens), and rice have been shown to have either mannan or glucomannan synthase activity when heterologously expressed (Dhugga et al, 2004;Liepman et al, 2005Liepman et al, , 2007Suzuki et al, 2006). The expression levels of six known barley CslA genes were followed over the differentiation phase of endosperm development.…”

CELLULOSE SYNTHASE-LIKE A2, a Glucomannan Synthase, Is Involved in Maintaining Adherent Mucilage Structure in Arabidopsis Seed

“…CSLA2, CSLA3, and CSLA9 are proposed to play nonredundant roles in the biosynthesis of stem glucomannans, although mutations in CSLA2, CSLA3, or CSLA9 have no effect on stem development or strength (Goubet et al, 2009). All of the Arabidopsis CSLA proteins have been shown to be involved in the biosynthesis of mannan polysaccharides in the plant cell wall (Liepman et al, 2005(Liepman et al, , 2007, although the precise physiological functions of only CSLA7 and CSLA9 have been conclusively demonstrated.In Arabidopsis, when mature dry seeds are hydrated, gel-like mucilage is extruded to envelop the entire seed. Ruthenium red staining of Arabidopsis seeds reveals two different mucilage layers, termed the nonadherent and the adherent mucilage layers (Western et al, 2000;Macquet et al, 2007a).…”

“…These enzymes polymerize the b-1,4-linked backbone of mannans or glucomannans, depending on the substrates (GDP-Man and/or GDP-Glc) provided (Richmond and Somerville, 2000;Liepman et al, 2005Liepman et al, , 2007Pauly et al, 2013). In Arabidopsis (Arabidopsis thaliana), nine CSLA genes have been identified; different CSLAs are responsible for the synthesis of different mannan types (Liepman et al, 2005(Liepman et al, , 2007 mannan synthase activity in vitro (Liepman et al, 2005) and has been shown to synthesize stem glucomannan in vivo (Goubet et al, 2009). Disrupting the CSLA7 gene results in defective pollen growth and embryo lethality phenotypes in Arabidopsis, indicating structural or signaling functions of mannan polysaccharides during plant embryo development (Goubet et al, 2003).…”

The Genetics and Transcriptional Profiles of the Cellulose Synthase-Like HvCslF Gene Family in Barley

“…Surprisingly few Csl genes have been assigned a specific function in plant cell wall biosynthesis. Members of the CslA subfamily encode (1,4)-b-D-mannan synthases (Dhugga et al, 2004;Liepman et al, 2007), and the CslC group is believed to encode an enzyme that directs the synthesis of the (1,4)-b-D-glucan backbone of xyloglucans (Cocuron et al, 2007). Using a comparative genomics approach, Burton et al (2006) showed that a cluster of the monocot-specific CslF genes in rice is located in a genomic region corresponding to one containing a major quantitative trait locus (QTL) for grain (1,3;1,4)-b-D-glucan content in barley (Hordeum vulgare).…”