Identification and overexpression of gibberellin 2‐oxidase (GA2ox) in switchgrass (Panicum virgatum L.) for improved plant architecture and reduced biomass recalcitrance

Abstract

SummaryGibberellin 2-oxidases (GA2oxs) are a group of 2-oxoglutarate-dependent dioxygenases that catalyse the deactivation of bioactive GA or its precursors through 2b-hydroxylation reaction. In this study, putatively novel switchgrass C 20 GA2ox genes were identified with the aim of genetically engineering switchgrass for improved architecture and reduced biomass recalcitrance for biofuel. Three C 20 GA2ox genes showed differential regulation patterns among tissues including roots, seedlings and reproductive parts. Using a transgenic approach, we showed that overexpression of two C20 GA2ox genes, that is PvGA2ox5 and PvGA2ox9, resulted in characteristic GA-deficient phenotypes with dark-green leaves and modified plant architecture. The changes in plant morphology appeared to be associated with GA2ox transcript abundance. Exogenous application of GA rescued the GA-deficient phenotypes in transgenic lines. Transgenic semi-dwarf lines displayed increased tillering and reduced lignin content, and the syringyl/guaiacyl lignin monomer ratio accompanied by the reduced expression of lignin biosynthetic genes compared to nontransgenic plants. A moderate increase in the level of glucose release in these transgenic lines might be attributed to reduced biomass recalcitrance as a result of reduced lignin content and lignin composition. Our results suggest that overexpression of GA2ox genes in switchgrass is a feasible strategy to improve plant architecture and reduce biomass recalcitrance for biofuel.

Identification and characterization of tomato gibberellin 2-oxidases (GA2oxs) and effects of fruit-specific SlGA2ox1 overexpression on fruit and seed growth and development

“…22 Serrani et al 6 identified only five putative GA2oxs in tomato ( SlGA2ox1 - SlGA2ox5 ), 6 however, in this study, eleven GA2ox genes were identified in the tomato genome, six of which ( SlGA2ox6 - SlGA2ox11 ) were newly identified (Supplementary Table S1). There are two possible explanations for this difference.…”

“…2 Application of exogenous GA 3 to unpollinated ovaries of tomato increases the fruit set, but the fruits are parthenocarpic with reduced sizes of locular tissues and fruits compared with pollinated fruits. 22 Conversely, exogenous treatment of pollinated ovaries with GA biosynthesis inhibitors decreases the fruit set, and the fruits are smaller than untreated pollinated fruits. 6,25–27 In addition, modifying the expression of the genes that regulate GA biosynthesis and deactivation can influence the endogenous GA levels and vegetative growth of tomato plants.…”

Candidate regulators of Early Leaf Development in Maize Perturb Hormone Signalling and Secondary Cell Wall Formation When Constitutively Expressed in Rice

“…Increased GA levels would explain the spindly phenotype of transgenic rice lines overexpressing ZmHBa and ZmHBb genes (Fig. 6c,d), either through a direct effect of GA on cell expansion or through an inhibition of lignin content (as previously reported in GA2OX overexpression lines of switchgrass) 43 . The third maize gene, referred to here as ZmHBc (GRMZM2G425236), grouped with AtHB23 , AtHB26 , AtHB29 , AtHB30 and AtHB34 .…”

Identification and Characterization of microRNA319a and Its Putative Target Gene, PvPCF5, in the Bioenergy Grass Switchgrass (Panicum virgatum)

“…Quantitative RT-PCR was performed on a Bio-Rad Chromo 4 Real-Time PCR System (Bio-Rad, Hercules, CA, USA) using a TransStart SYBR Green qPCR SuperMix Kit (TransGen, Beijing, China). A switchgrass ubiquitin gene was used as a control (Wuddineh et al, 2015) (Switchgrass Unitranscript ID: AP13CTG25905). Expression levels of examined genes were quantified by a relative quantitation method, each sample was subjected to at least three biological replicates in this experiment.…”