Overexpression of miR156 in switchgrass (Panicum virgatum L.) results in various morphological alterations and leads to improved biomass production

Abstract

Switchgrass (Panicum virgatum L.) has been developed into a dedicated herbaceous bioenergy crop. Biomass yield is a major target trait for genetic improvement of switchgrass. microRNAs have emerged as a prominent class of gene regulatory factors that has the potential to improve complex traits such as biomass yield. A miR156b precursor was overexpressed in switchgrass. The effects of miR156 overexpression on SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) genes were revealed by microarray and quantitative RT-PCR analyses. Morphological alterations, biomass yield, saccharification efficiency and forage digestibility of the transgenic plants were characterized. miR156 controls apical dominance and floral transition in switchgrass by suppressing its target SPL genes. Relatively low levels of miR156 overexpression were sufficient to increase biomass yield while producing plants with normal flowering time. Moderate levels of miR156 led to improved biomass but the plants were non-flowering. These two groups of plants produced 58%–101% more biomass yield compared with the control. However, high miR156 levels resulted in severely stunted growth. The degree of morphological alterations of the transgenic switchgrass depends on miR156 level. Compared with floral transition, a lower miR156 level is required to disrupt apical dominance. The improvement in biomass yield was mainly because of the increase in tiller number. Targeted overexpression of miR156 also improved solubilized sugar yield and forage digestibility, and offered an effective approach for transgene containment.

Differential Expression of MicroRNAs Between 21A Genetic Male Sterile Line and Its Maintainer Line in Cotton (Gossypium hirsutum L.)

“…miR164 targets NAC transcription factor, and miR167 targets auxin response factors that play roles in plant signaling transduction and root development. It is interesting to note that those transcription factors are similar to those reported previously as miRNA targets for other plant species (Mallory et al, 2004;Arazi et al, 2005;Wu et al, 2006;Yang et al, 2006;Fu et al, 2012). In this study, we also found that scarecrow-like (SCL) protein 22 and mitochondrial transcription termination factor have near-perfect complementary sites with miR171 and miR426, respectively.…”

Transgenic switchgrass (Panicum virgatum L.) targeted for reduced recalcitrance to bioconversion: a 2‐year comparative analysis of field‐grown lines modified for target gene or genetic element expression

“…Field‐grown switchgrass transgenic lines with high sugar release or good growth phenotypes included those silencing or OE: (i) GAUT4, GAUT4 ‐knockdown (KD) lines down‐regulating expression of galacturonosyltransferase4 , a gene encoding an enzyme involved in pectin biosynthesis (Biswal et al ., Biswal, A.K., Atmodjo, M.A., Li, M., Yoo, C.G., Pu, Y., Lee, Y.‐C., Zhang, J.Y., Bray, A., King, Z., LaFayette, P., Mohanty, S.S., Ryno, D., Yee, K., Thompson, O.A., Rodriguez Jr, M., Winkeler, K., Collins, C., Yang, X., Tan, L., Sykes, R.W., Gjersing, E., Ziebell, A., Turner, G.B., Decker, S.R., Parrot, W., Udvardi, M.K., Mielenz, J., Davis, M.F., Nelson, R.S., Ragauskas, A.J., and Mohnen, D.); (ii) miRNA, miRNA156 ‐overexpression (OE) lines OE miRNA156, a regulator of plant developmental processes (Fu et al ., 2012); (iii) MYB4, MYB4 ‐OE lines OE PvMYB4, an R2R3‐type MYB repressor of the lignin biosynthetic pathway (Shen et al ., 2012, 2013); (iv) COMT, COMT ‐KD lines down‐regulating expression of caffeic acid O ‐methyltransferase, a lignin biosynthetic gene (Fu et al ., 2011); and (v) FPGS, FPGS ‐KD lines down‐regulating expression of folylpolyglutamate synthase 1 , a gene encoding a C1 metabolism enzyme believed to provide methyl groups for lignin biosynthesis (Srivastava et al ., 2015). …”

Senescence, dormancy and tillering in perennial C4 grasses

“…Conventional and transgenic approaches have been utilized to generate switchgrasses with improved quality, based primarily on the reduction of lignin content as a means to improve ethanol yields through fermentation of biomass [73,[122][123][124][125], and possibly for increased yields or plant development using transgenic routes [126,127]. The application of biotechnology for switchgrass improvement has been reviewed recently [17].…”