Metabolic Induction of N Storage and Cycling in Poplar is Associated with Wide-spread Changes in the Bark Transcriptome and Proteome

N storage is a fundamental physiological and metabolic process that occurs on a number of time scales including daily, weekly, seasonal and lifetime. Understanding how plants use resources, such as N, and the components that contribute to economy of use are basic to understanding plant growth, plant competition and ecosystem function.  Temperate deciduous trees have an exceptional capacity to store and reuse N on both short-term and seasonal time frames.  In poplar, Bark Storage Proteins (BSP) play a central role in both short-term and seasonal N storage and cycling.  To identify metabolic and regulatory networks and pathways associated with poplar N storage and cycling we have profiled genome-wide changes in the bark transcriptome and proteome using an excised stem assay that allows for the efficient induction of BSP gene expression by selected metabolites.  Using the Affymetrix Poplar Genome GeneChip and gel-based proteomics we profiled changes of both transcripts and proteins in the bark of excised stems that were treated with glutamine, glucose, or glutamine combined with glucose to an untreated (water) control.  Significant changes were found for both the glutamine and glutamine combined with glucose treatment but surprisingly the glucose treatment did not reveal any significant changes in gene expression or protein accumulation.  Although both treatments with glutamine and glutamine combined with glucose shared a common set of genes with altered expression, genes specific to either the glutamine or the glutamine combined with glucose were also detected.  This finding demonstrates an interaction between glucose and glutamine in the metabolic regulation of gene expression in this system.  Funded by NSF grant IOS0922650