Isolating promoters of multigene family members from the polyploid sugarcane genome by PCR-based walking in BAC DNA.

The availability of a wider range of promoters for regulated expression in valuable transgenic crops would benefit functional genomics studies and current biotechnology programs aimed at improved productivity. Polymerase chain reaction (PCR)-based genome walking techniques are commonly used to isolate promoters or 5' flanking genomic regions adjacent to known cDNA sequences in genomes that are not yet completely sequenced. However, these techniques are problematic when applied directly to DNA isolated from crops with highly complex and large genomes. An adaptor ligation-mediated PCR-based BAC genome walking method is described here for the efficient isolation of promoters of multigene family members, such as the putative defense and fiber biosynthesis DIRIGENT genes that are abundant in the stem of sugarcane, a species with a highly polyploid genome. The advantage of this method is the efficient and specific amplification of the target promoter using BAC genomic DNA as template for the adaptor ligation-mediated PCR walking.