Bacterial artificial chromosome (BAC) libraries are often the starting point for genomic enablement of any given species. BACs are the vector of choice for cloning and exploiting long stretches of genomic DNA ranging from 120­350kb in size and are relatively stable with low levels of chimeric content and can be safely stored and accessed in a standard molecular biology laboratory. A deep coverage BAC library with at least 10X redundancy produced from multiple restriction enzymes can serve an essential role in whole genome physical mapping, positional cloning, integration of genetic markers, and through the extraction of a minimal tiling path (MTP) a template for accurate genome reconstruction and targeted genome finishing. Currently, there are two reports for available BAC resources for switchgrass; an EcoRI restriction derived BAC library from the SL93 2001-1 Alamo genotype (Saski et al. 2011) and two complimentary restriction derived BACs created with HindIII and BstYI, respectively, of the AP13 genotype (Sharma et al.

2012) . The first BAC efforts by Saski et al. represents approximately 10 haploid genome equivalents based on a 3.2 Gbp estimated genome size. The BAC was constructed by partial digestion with EcoRI and contains 147,456 clones with an average insert size of 120kb, and is publicly available through the Clemson University Genomics Institute (www. genome. clemson. edu) (Saski et al. 2011). Saski et al. screened the BAC library with a rice brassinosteroid insensitive homolog, OsBRIl, which exhibits a dwarf phenotype when knocked out in rice and maize to assess the feasibility of sub-genome organization and potential for homeologous resolution through High Information Content Fingerprinting (HICF). Through this study, the authors point out that orthologous BACs containing the OsBRI1 locus were identified on homeologous BACs that can be distinguished through HICF. Two BACs were sequenced to completion and a comparison of the suspected homeologous regions suggest preservation of gene order to closely related grasses, yet significant fractionation. These data suggest the switchgrass sub-genomes are similar enough to discover homeologous segments, yet divergent enough to allow for sub-genome placement (Saski et al. 2011). As a follow up study and additional BAC effort, Sharma et al. (2012) produced two additional deep coverage BAC libraries from the AP13 clone (Missaoui et al. 2005), which has been widely used for mapping efforts (Missaoui et al. 2005). The AP13 BACs, PV_ABa and PV_ABb were constructed by partial digestion using complimentary restriction enzymes, HindIII and BstYI, respectively. The average insert sizes are 144kb and 110kb for PV_Aba and PV_ABb, respectively. Combined, these BAC resources represent 16 haploid genome equivalents and are publicly available through the Clemson University Genomics Institute (www. genome. clemson. edu). The authors exploit these BAC libraries through BAC-end, and full-BAC sequencing and comparative mapping in an effort to characterize genome structure and composition, and provide long-range connectivity to the ongoing switchgrass reference genome activities (Sharma et al. 2012). The results of sequencing 47 full-length BACs and close to 330k BAC-end sequences and aligning these resources with available grass genome sequences such as rice, sorghum, maize, and Brachypodium suggest that switchgrass retains a higher degree of microsynteny with sorghum and high gene order and conservation with rice, but is largely collinear with these grass genomes in general (Sharma et al. 2012). These resources present a valuable framework for functional, comparative, and genome reconstruction efforts.