Molecular cloning of a peroxidase gene from poplar and its expression in response to stress

To elucidate the precise functions of peroxidase in poplar (Populus alba x P. tremula var. glandulosa), we cloned a peroxidase gene (PoPOD1) from poplar suspension culture cells and examined its expression pattern in response to various stresses. PoPOD1 showed the highest homology with a bacterial-induced peroxidase gene from cotton (Gossypium hirsutum L.). The PoPOD1 gene encodes a putative 316 amino acid protein with an N-terminal signal peptide of 23 residues. The DNA blot analysis indicated that PoPOD1 is a single copy gene in the poplar genome. The RNA blot analyses indicated that PoPOD1 shows cell-culture-specific expression. Expression of PoPOD1 is down-regulated by various treatments including treatment with some metals, NaCl, methyl viologen and polyethylene glycol, and by the plant growth regulators, jasmonic acid (JA) and gibberellic acid (GA(3)). The gene is significantly up-regulated by the bacterial-elicitor laminarin and by wounding. Thus, PoPOD1 gene expression is sensitively and specifically regulated at the transcription level. Because both JA and GA3 appear to be involved in the regulation of PoPOD1 expression in poplar cells, we postulate that the peroxidase encoded by PoPOD1 plays a pivotal role in defense against pathogen invasion, possibly through the formation of a cell wall barrier over the wound.