Transcriptional Analysis of Switchgrass Flowering Time

Over the past two decades, switchgrass (Panicum virgatum) has emerged as a viable biofuel feedstock. The bulk of switchgrass biomass is in the vegetative portion of the plant; a longer vegetative stage leads to increase in overall biomass yield. The goal of this study was to gain insight into the components of the flowering time pathway in switchgrass, to assist in developing varieties that have extended vegetative phases through delayed flowering. The approach examined differential gene expression between switchgrass genotypes of early- and late-flowering ecotypes. Shoot apical meristem (SAM) and leaf tissue were collected in a developmental series from emergence to anthesis to capture stages of both vegetative and reproductive growth. The morphology of the SAM was also tracked to determine the stage of meristem transition and to choose samples that flanked the SAM transition for sequencing and expression analyses. The analyses revealed differential expression patterns between early- and late-flowering genotypes for known flowering time orthologs, as well as several novel genes, some of which are related to known flowering time genes. In addition, based on expression patterns, many of the identified genes could be classified as putative promoters or repressors of flowering. The candidate genes presented here will be further supported by functional confirmation in switchgrass or the model grass, Brachypodium, and may be used to guide switchgrass improvement through marker assisted breeding and/or gene transformation methods.