Wuddineh Wegi A, Mazarei Mitra, Zhang Ji-Yi, Turner Geoffrey B, Sykes Robert W, Decker Stephen R, Davis Mark F, Udvardi Michael K, Stewart C Neal
Department of Plant Sciences, University of TennesseeKnoxville, TN, USA; BioEnergy Science Center, Oak Ridge National LaboratoryOak Ridge, TN, USA.
BioEnergy Science Center, Oak Ridge National LaboratoryOak Ridge, TN, USA; Plant Biology Division, Samuel Roberts Noble FoundationArdmore, OK, USA.
Front Plant Sci. 2016 Apr 28;7:520. doi: 10.3389/fpls.2016.00520. eCollection 2016.
High biomass production and wide adaptation has made switchgrass (Panicum virgatum L.) an important candidate lignocellulosic bioenergy crop. One major limitation of this and other lignocellulosic feedstocks is the recalcitrance of complex carbohydrates to hydrolysis for conversion to biofuels. Lignin is the major contributor to recalcitrance as it limits the accessibility of cell wall carbohydrates to enzymatic breakdown into fermentable sugars. Therefore, genetic manipulation of the lignin biosynthesis pathway is one strategy to reduce recalcitrance. Here, we identified a switchgrass Knotted1 transcription factor, PvKN1, with the aim of genetically engineering switchgrass for reduced biomass recalcitrance for biofuel production. Gene expression of the endogenous PvKN1 gene was observed to be highest in young inflorescences and stems. Ectopic overexpression of PvKN1 in switchgrass altered growth, especially in early developmental stages. Transgenic lines had reduced expression of most lignin biosynthetic genes accompanied by a reduction in lignin content suggesting the involvement of PvKN1 in the broad regulation of the lignin biosynthesis pathway. Moreover, the reduced expression of the Gibberellin 20-oxidase (GA20ox) gene in tandem with the increased expression of Gibberellin 2-oxidase (GA2ox) genes in transgenic PvKN1 lines suggest that PvKN1 may exert regulatory effects via modulation of GA signaling. Furthermore, overexpression of PvKN1 altered the expression of cellulose and hemicellulose biosynthetic genes and increased sugar release efficiency in transgenic lines. Our results demonstrated that switchgrass PvKN1 is a putative ortholog of maize KN1 that is linked to plant lignification and cell wall and development traits as a major regulatory gene. Therefore, targeted overexpression of PvKN1 in bioenergy feedstocks may provide one feasible strategy for reducing biomass recalcitrance and simultaneously improving plant growth characteristics.
高生物量产量和广泛的适应性使柳枝稷（Panicum virgatum L.）成为木质纤维素生物能源作物的重要候选者。这种以及其他木质纤维素原料的一个主要限制是复杂碳水化合物对水解转化为生物燃料的抗性。木质素是导致抗性的主要因素，因为它限制了细胞壁碳水化合物被酶分解为可发酵糖的可及性。因此，对木质素生物合成途径进行基因操作是降低抗性的一种策略。在此，我们鉴定了一种柳枝稷Knotted1转录因子PvKN1，旨在通过基因工程改造柳枝稷，降低其生物量抗性以用于生物燃料生产。观察到内源性PvKN1基因在幼嫩花序和茎中的基因表达最高。PvKN1在柳枝稷中的异位过表达改变了生长，尤其是在早期发育阶段。转基因株系中大多数木质素生物合成基因的表达降低，同时木质素含量减少，这表明PvKN1参与了木质素生物合成途径的广泛调控。此外，转基因PvKN1株系中赤霉素20-氧化酶（GA20ox）基因表达降低，同时赤霉素2-氧化酶（GA2ox）基因表达增加，这表明PvKN1可能通过调节GA信号发挥调控作用。此外，PvKN1的过表达改变了纤维素和半纤维素生物合成基因的表达，并提高了转基因株系中的糖释放效率。我们的结果表明，柳枝稷PvKN1是玉米KN1的假定直系同源基因，作为主要调控基因与植物木质化、细胞壁和发育性状相关。因此，在生物能源原料中有针对性地过表达PvKN1可能为降低生物量抗性并同时改善植物生长特性提供一种可行的策略。
