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Overexpression of SbMyb60 impacts phenylpropanoid biosynthesis and alters secondary cell wall composition in Sorghum bicolor

Scully, Erin D., Gries, Tammy, Sarath, Gautam, Palmer, Nathan A., Baird, Lisa, Serapiglia, Michelle J., Dien, Bruce S., Boateng, Akwasi A., Ge, Zhengxiang, Funnell‐Harris, Deanna L., Twigg, Paul, Clemente, Thomas E., Sattler, Scott E.
The plant journal 2016 v.85 no.3 pp. 378-395
C4 plants, Sorghum bicolor, anthocyanins, biochemical pathways, bioenergy, biomass, biosynthesis, cell wall components, drought tolerance, energy crops, feedstocks, gene expression regulation, genes, grasses, leaves, lignification, lignin, phenolic compounds, transcription factors, transgenic plants
The phenylpropanoid biosynthetic pathway that generates lignin subunits represents a significant target for altering the abundance and composition of lignin. The global regulators of phenylpropanoid metabolism may include MYB transcription factors, whose expression levels have been correlated with changes in secondary cell wall composition and the levels of several other aromatic compounds, including anthocyanins and flavonoids. While transcription factors correlated with downregulation of the phenylpropanoid biosynthesis pathway have been identified in several grass species, few transcription factors linked to activation of this pathway have been identified in C4 grasses, some of which are being developed as dedicated bioenergy feedstocks. In this study we investigated the role of SbMyb60 in lignin biosynthesis in sorghum (Sorghum bicolor), which is a drought‐tolerant, high‐yielding biomass crop. Ectopic expression of this transcription factor in sorghum was associated with higher expression levels of genes involved in monolignol biosynthesis, and led to higher abundances of syringyl lignin, significant compositional changes to the lignin polymer and increased lignin concentration in biomass. Moreover, transgenic plants constitutively overexpressing SbMyb60 also displayed ectopic lignification in leaf midribs and elevated concentrations of soluble phenolic compounds in biomass. Results indicate that overexpression of SbMyb60 is associated with activation of monolignol biosynthesis in sorghum. SbMyb60 represents a target for modification of plant cell wall composition, with the potential to improve biomass for renewable uses.