Abstract
Previous cDNA microarray analysis data from the xylem tissue of gibberellin (GA) over-producing transgenic hybrid aspen (Populus tremula×P. tremuloides) with increased secondary growth, has shown pectate lyase (Pel) and arabinogalactan peptide (AGp) encoding genes to be highly up-regulated when compared to WT. These genes have been demonstrated to be highly expressed in the cell division and cell expansion zones of WT developing xylem. These results suggest that Pel and AGp are important in the early stages of secondary growth and that the expression might be affected by GAs. We have cloned putative full-length cDNA clones of both PttPell and PttAGp1 from hybrid aspen. The PttPell deduced amino acid sequence exhibited high similarity to several plant Pel, and the PttAGp1 deduced amino acid sequence showed high homology to Arabidopsis AGp's AtAGP12,AtAGP13 and AtAGP14,which have very short GPI-anchored protein backbones. To evaluate the role of GAs in inducing the transcription of PttPell and PttAGp1,the expression patterns of respective genes in (GA)_4 infiltrated hybrid aspen plants compared to non-treated plants have been examined. The results showed that the expression level of both PttPell and PttAGp1 have been up-regulated by GA treatment. To further investigate the role of PttPell and PttAGp1,the genes were independently over-expressed under the CaMV 35S promoter in Arabidopsis thaliana. Finally, experiments are underway to analyse the enzyme activity of PttPell using recombinant proteins, and to determine the protein backbone amino acid sequence of PttAGp1 isolated from hybrid aspen by using LC/MS.
