Abstract
BackgroundSwitchgrass (Panicum virgatum L.), a C4 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 TCP genes. We hypothesized miR319–TCP pathway could play important roles in switchgrass feedstock characteristics for biofuel production, and produced switchgrass transgenic plants overexpressing miR319 (by ectopic expressing Osa-MIR319b gene), blocking miR319 (by overexpressing a target mimicry of miR319/MIM319) and repression of miR319 target gene PvPCF5. Plant phenotype, biomass yield, and feedstock quality of transgenic plants were analyzed.ResultsOverexpression 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 MIM319 plants. Furthermore, suppression of miR319 target gene PvPCF5 activity also reduced lignin content, increased lignin monomer S/G ratio and the proportion of β-O-4 linkages, while significantly improving the sugar production per plant. Quantitative real-time (qRT-PCR) analysis indicated that expression of PvMYB58/63B and PvHCT with predicted TCP binding sites in their promoter regions was negatively regulated by miR319–PvPCF5 module.ConclusionsMiR319–PvPCF5 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.
Highlights
Switchgrass (Panicum virgatum L.), a C4 perennial grass, has been recognized as one of the most potentially important lignocellulose biofuel crops
Expression profiles of miR319 and its target genes in switchgrass stems To explore the function of miR319 and its target gene PvTCPs in switchgrass stem growth, development, and lignin deposition, we first tested the relative expression levels of miR319 and PvTCPs in four segments of the second internode from the top of the plant (Additional file 1: Figure S1a)
The results indicated that suppression of PvPCF5 reduced switchgrass lignin content mainly by reducing G unit content, which resulted in a higher S/G ratio in 5sr plants compared to wild type (WT) plant
Summary
Switchgrass (Panicum virgatum L.), a C4 perennial grass, has been recognized as one of the most potentially important lignocellulose biofuel crops. MYELOBLASTOSIS (MYB), NAM/ATAF/CUC (NAC), and APETALA2/Ethylene Responsive Factor (AP2/ERF) families [11,12,13,14], could efficiently alter lignin composition and structure and/or secondary cell wall remodeling, leading to enhanced sugar release efficiently [reviewed in 15, 16]. Those improvements were accompanied with potential side effects such as stunted plant growth [11,12,13], sterile characteristics [12], or sensitivity to biotic and/or abiotic stresses [17, 18]. It is highly desirable to determine alternative methods of lignin engineering that can increase cell wall digestibility with a minimum impact on plant fitness and yield
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