Identification of Candidate Genes Using Rice Mutants for Biomass Engineering in Switchgrass

Developing a sustainable biofuels program that makes significant contributions to the national energy budget requires unprecedented inputs of biomass for energy conversion.  Our specific objectives are to identify genes and pathways in rice (Oryza sativa) that increase plant biomass in order to translate this information into cultivar improvement for new energy crops, such as switchgrass.  We have screened over 12,000 chemical and irradiation-induced mutants of rice and identified 13 mutants with increased biomass.  Our initial effort focused on one diepoxybutane mutant (DEB1) that has reproducibly shown a two-fold increase in biomass under both field and greenhouse conditions.  DEB1 plants are also taller and have more tillers, seed yield, and girth than wild-type plants.  Diepoxybutane is predicted to cause small deletions in the genome and to identify the deletions in DEB1, we first backcrossed the mutant to IR64 and then sequenced F2 individuals segregating for the biomass phenotype (Illumina HiSeq 100 bp paired end reads).  We identified 49 indels, ranging in size from 1 to 153 bps, common to all high biomass individuals.  Identification of the indel responsible for the high biomass phenotype is currently in progress.