Biosynthesis, Developmental Anatomy, and Transcriptional Regulation of the Brachypodium distachyon Stem

A defining aspect of plant cell function is the wall. Once a cell has taken final shape, some specialized cell types, namely those found in stem including tracheary elements and sclerenchyma cells, undergo secondary cell wall thickening. Grass cell walls are mostly comprised of three different components: cellulose, hemicellulose, and lignin. Cellulose is an integral component and accounts for approximately forty percent of total plant biomass but understanding of its mechanism of synthesis remains elusive. Lignin is a significant recalcitrant in the conversion of plant biomass to bioethanol. We investigated the internal stem anatomy of the model system Brachypodium distachyon and found it to be highly similar to domesticated grasses but rather distinct from Arabidopsis thaliana. To better understand the biosynthesis and regulation of secondary cell walls in grasses, we first identified candidate genes putatively encoding CESA, CAD and COMT enzymes in B. distachyon and functionally characterize loss-of-function mutants generated using artificial microRNA constructs. The cis-regulatory regions of these genes were used as DNA-bait against a collection of transcription factor proteins to resolve their regulators. The results suggest regulatory nodes potentially unique to grasses and some orthologous to dicots.