Genetic engineering of switchgrass (Panicum virgatum L.) for reduced cell
wall recalcitrance and improved biofuel production has long been a goal.
Promoters have been used to control the expression of cell wall synthesis
genes toward the goal. However, these often lead to undesirable plant
phenotypic effects. Green tissue-specific promoters from switchgrass are
potentially valuable to alter cell wall traits while not changing
The team of Wusheng Liu, Mitra Mazarei, and Rongjian Ye from the University
of Tennessee in the USA studied three switchgrass green tissue-specific
promoters in rice. They then used them to direct the expression of the
switchgrass PvMYB4 transcription factor gene in transgenic switchgrass to
confer reduced recalcitrance in aboveground biomass.
Analysis detected the strong expression of the PvMYB4 in the aboveground
tissues, including leaf blades, leaf sheaths, internodes, inflorescences,
and nodes of switchgrass. The green tissue-specific expression of PvMYB4 in
transgenic switchgrass led to significant gains in saccharification
efficiency and decreased levels of lignin. Furthermore, plant growth was not
compromised in green tissue-expressed PvMYB4 switchgrass plants.
This study suggests that green tissue-specific expression of PvMYB4 is an
effective strategy for the improvement of transgenic feedstocks.