An efficient Agrobacterium-mediated transformation method for switchgrass genotypes using Type I callus

摘要

Switchgrass (Panicum virgatum L.) is an important bioenergy crop. A reliable and efficient transformation method is required to assist with molecular breeding of this crop. In this study, we established a simple and efficient Agrobacterium-mediated transformation method for caryopsis-derived Type I callus by optimizing the cocultivation (7 days at 22 degrees C on medium supplemented with 10 g l(-1) glucose and 100 mu M acetosyringone) and preculture (2 weeks on medium supplemented with 5 g l-1 casamino acids after cell straining) conditions without the need for time-consuming treatments before and after cocultivation. The present transformation method was successfully applied to different genotypes of switchgrass including a recalcitrant lowland cultivar. The transformation efficiencies of callus lines of the lowland cultivars 'Alamo' and 'Kanlow' were 12.5-59% and 6.3-20%, respectively. An upland cultivar 'Trailblazer' formed Type I calli and one of three tested callus lines produced transgenic plants at relatively high efficiency (7.5%). In contrast, Type I callus formation was unsuccessful for two other upland cultivars, 'Blackwell' and 'Cave-in-Rock.' This simple and efficient transformation method is suitable for routine and large-scale experiments due to its ready availability of caryopses, prevalence of Type I callus formation, and longevity in the regeneration ability of the callus.