A High Throughput Switchgrass Genetic Transformation System for Gene Function Discovery and Genetic Improvement

Switchgrass (Panicum virgatum L.) is a tall growing perennial C4 grass providing excellent forage for cattle and substantial feedstock for biofuel production. Genetic engineering for the improvement of forage quality and bioethanol yield has received more attention in switchgrass molecular breeding programs. With increasing information on gene sequences in switchgrass, large numbers of genes can be isolated in a relatively short time, while functional analyses of the isolated genes by genetic transformation have become a bottleneck. To produce large numbers of transgenic switchgrass plants with low cost and short time, we screened numerous seed-induced calli to obtain the high-quality embryogenic callus lines, and thereafter developed sonication-assisted Agrobacterium-mediated transformation (SAAT) to increase Agrobacterium infection efficiency and decrease labor force. The transformation efficiency reached more than 80%. One person easily produced more than 1, 000 independent transgenic switchgrass lines in six months. Moreover, we established a simple and reliable multi-gene transformation system. The transformants were successfully selected by double selectable reagents, hygromycin and bialaphos. The transgenics showed various morphological phenotypes, indicating that our high throughput switchgrass transformation system can be employed for gene function discovery and genetic improvement.