Abstract
BackgroundThe ability to increase cellulose content and improve the stem strength of cereals could have beneficial applications in stem lodging and producing crops with higher cellulose content for biofuel feedstocks. Here, such potential is explored in the commercially important crop barley through the manipulation of cellulose synthase genes (CesA).ResultsBarley plants transformed with primary cell wall (PCW) and secondary cell wall (SCW) barley cellulose synthase (HvCesA) cDNAs driven by the CaMV 35S promoter, were analysed for growth and morphology, transcript levels, cellulose content, stem strength, tissue morphology and crystalline cellulose distribution. Transcript levels of the PCW HvCesA transgenes were much lower than expected and silencing of both the endogenous CesA genes and introduced transgenes was often observed. These plants showed no aberrant phenotypes. Although attempts to over-express the SCW HvCesA genes also resulted in silencing of the transgenes and endogenous SCW HvCesA genes, aberrant phenotypes were sometimes observed. These included brittle nodes and, with the 35S:HvCesA4 construct, a more severe dwarfing phenotype, where xylem cells were irregular in shape and partially collapsed. Reductions in cellulose content were also observed in the dwarf plants and transmission electron microscopy showed a significant decrease in cell wall thickness. However, there were no increases in overall crystalline cellulose content or stem strength in the CesA over-expression transgenic plants, despite the use of a powerful constitutive promoter.ConclusionsThe results indicate that the cellulose biosynthetic pathway is tightly regulated, that individual CesA proteins may play different roles in the synthase complex, and that the sensitivity to CesA gene manipulation observed here suggests that in planta engineering of cellulose levels is likely to require more sophisticated strategies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0448-y) contains supplementary material, which is available to authorized users.
Highlights
The ability to increase cellulose content and improve the stem strength of cereals could have beneficial applications in stem lodging and producing crops with higher cellulose content for biofuel feedstocks
Barley cellulose synthase (HvCesA) genes are distributed across the grass genome At least eight barley (Hordeum vulgare) HvCesA genes were identified by Burton and co-authors [15]
In silico mapping of HvCesA genes in barley and two other economically important grasses, Sorghum bicolor and Oryza sativa indicated that the cellulose synthase genes (CesA) genes are broadly distributed across the genomes, especially so in barley where HvCesA genes are found on every chromosome except chromosome 4
Summary
The ability to increase cellulose content and improve the stem strength of cereals could have beneficial applications in stem lodging and producing crops with higher cellulose content for biofuel feedstocks. Such potential is explored in the commercially important crop barley through the manipulation of cellulose synthase genes (CesA). Cellulose microfibrils are generally arranged perpendicular to the axis of cell elongation, the alignment between microfibrils is not strictly parallel Such an arrangement of microfibrils provides both strength and flexibility that enable the primary cell walls to withstand turgor pressure and to assist in the cell’s directional growth. There can be several layers in secondary walls and within each layer the parallel microfibrils can be oriented at different angles to create laminated layers that further strengthen the wall and restrict the cell’s lateral or radial growth
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