Genome-wide transcript profiling associated with metabolic regulation of Poplar N storage and cycling

Previous research has shown that glutamine and sucrose treatment of excised poplar stems induces bark storage protein (BSP) gene expression. The objective of this research is to identify changes in gene expression associated with metabolic regulation of nitrogen storage and cycling and use this information to identify potential regulatory genes. Significant, differentially expressed genes were identified in excised poplar stems incubated in solutions of glutamine, sucrose, glycine, glutamine+glucose, and glutamine+sucrose compared to incubation in a water control. Poplar shoots with approximately 10 nodes were excised from greenhouse stock plants that were grown in LD photoperiods. The basal leaves were removed to leave only the 5 apical leaves. The basal ends of the 5-leaved shoots were pre-incubated by placing in water for 24 h in a growth chamber (20 °C, 16-light/8-h dark). Following a 24 h pre-incubation, the excised stems were then transferred to 25 mM aqueous solutions of glutamine, glucose, sucrose, glycine, glutamine+glucose or glutamine+sucrose as well as a water control and incubated for either 48 or 72 h. Solutions were replenished at 24 h intervals to maintain an approximate volume of 0.5 L. After 48 h and 72 h of incubation in the respective solutions, bark tissue was collected from each treatment and immediately frozen in liquid nitrogen. For each treatment, 3 biological replicates were collected with 5 excised stems per biological replicate. Bark from 2 pre-treatments consisting of 3 biological replicates was also collected. Bark of the 'pre1' was collected immediately after excising from the stock plants and 'pre2' bark was collected after the 24 h pre-incubation period.