Expression Analysis of Auxin Regulated Genes in Populus

Due to its many advantageous characteristics, such as a small sequenced genome, ease of vegetative propagation and availability of genomic tools and databases, Populus is widely becoming accepted as the model species among trees. In addition, DOE has chosen hybrid poplar as the model bioenergy feedstock tree. Due to the growing importance of the Populus species, genetic and genomic resources (EST and BLAST databases, genetic maps, etc.) are becoming increasingly available and are leading to a greater understanding of the functionality of the Populus genome. The goal of this study was to use these resources to further characterize the genetic controls of root growth and development so that these mechanisms may eventually be manipulated to improve carbon sequestration ability in belowground sinks. Because auxin is known to play an important role in lateral root growth as well as many other aspects of plant development, a sequenced subtracted cDNA library from poplar was used to study the expression of genes up and down-regulated in response to exogenous auxin treatments. Results from this study indicate that a daily 9-day exogenous auxin treatment may have induced a stress response as indicated by the high percentage of WRKY transcription factors and stress related proteins that were up-regulated in response to the treatment regimen. A second study was also done using whole-genome oligonucleotide microarray technology to further analyze auxin regulated gene expression including Populus homologs of AUX/IAA and ARF genes in Arabidopsis. Results from this study did not appear to correlate well with real-time RT-PCR results indicating that, in the future, more reps need to be used to give the experiment the statistical power necessary to accurately find differentially expressed genes. Results from these gene expression studies can then be used to guide the development of poplar transgenics with increased root growth.