Heteroexpression of - improved switchgrass biomass yield and feedstock quality by repression of .

Background: Switchgrass ( L.), a C perennial grass, has been recognized as one of the most potentially important lignocellulose biofuel crops. MicroRNA319 (miR319) plays a key role in plant development, abiotic resistance, and cell wall biosynthesis by repressing expression of its target genes. We hypothesized miR319- pathway could play important roles in switchgrass feedstock characteristics for biofuel production, and produced switchgrass transgenic plants overexpressing miR319 (by ectopic expressing - gene), blocking miR319 (by overexpressing a target mimicry of miR319/) and repression of miR319 target gene . Plant phenotype, biomass yield, and feedstock quality of transgenic plants were analyzed.

Results: Overexpression of miR319 in switchgrass promoted leaf elongation and expansion of transgenic plants, increased plant height, stem diameter, and resulted in a significant increase in plant biomass yield. Transgenic plants overexpressing of miR319 reduced lignin content, showed significantly higher enzymatic hydrolysis efficiency compared to the wild type plant. However, opposite results were observed in the plants. Furthermore, suppression of miR319 target gene activity also reduced lignin content, increased lignin monomer S/G ratio and the proportion of β--4 linkages, while significantly improving the sugar production per plant. Quantitative real-time (qRT-PCR) analysis indicated that expression of and with predicted TCP binding sites in their promoter regions was negatively regulated by miR319- module.

Conclusions: MiR319- module plays positive roles in regulating biomass yield and quality of switchgrass. It can be utilized as a candidate molecular tool in regulating biomass yield and feedstock quality. The finding could also be transferred to other grasses for forage quality improvement through genetic manipulation.