Hybridization of downregulated-COMT transgenic switchgrass lines with field-selected switchgrass for improved biomass traits

Abstract

Transgenic switchgrass (Panicum virgatum L.) has been produced for improved cell walls for biofuels. For instance, downregulated caffeic acid 3-O-methyltransferase (COMT) switchgrass produced significantly more biomass and biofuel than the non-transgenic progenitor line. In the present study we sought to further improve biomass characteristics by crossing the downregulated COMT T₁ lines with high-yielding switchgrass accessions in two genetic backgrounds (‘Alamo’ and ‘Kanlow’). Crosses and T₂ progeny analyses were made under greenhouse conditions to assess maternal effects, plant morphology and yield, and cell wall traits. Female parent type influenced morphology, but had no effect on cell wall traits. T₂ hybrids produced with T₁ COMT-downregulated switchgrass as the female parent were taller, produced more tillers, and produced 63 % more biomass compared with those produced using the field selected accession as the female parent. Transgene status (presence or absence of transgene) influenced both growth and cell wall traits. T₂ transgenic hybrids were 7 % shorter 80 days after sowing and produced 43 % less biomass than non-transgenic null-segregant hybrids. Cell wall-related differences included lower lignin content, reduced syringyl-to-guaiacyl (S/G) lignin monomer ratio, and a 12 % increase in total sugar release in the T₂ transgenic hybrids compared to non-transgenic null segregants. This is the first study to evaluate the feasibility of transferring the low-recalcitrance traits associated with a transgenic switchgrass line into high-yielding field varieties in an attempt to improve growth-related traits. Our results provide insights into the possible improvement of switchgrass productivity via biotechnology paired with plant breeding.