Differential induction of ornithine decarboxylase (ODC) gene family members in transgenic tobacco (Nicotiana tabacum L. cv. Bright Yellow 2) cell suspensions by methyl-jasmonate treatment

Abstract

Two nuclear genes (NtODC-1 and NtODC-2) encoding ornithine decarboxylase (ODC, EC 4.1.1.17) were characterized from tobacco (Nicotiana tabacum L., and their differential induction by methyl-jasmonate (MeJA) was analyzed. ODC transcript levels increased in BY-2 cells following treatment with MeJA, with the highest levels of transcript observed approximately 5 h post-treatment. Analysis of transgenic BY-2 cell lines expressing a β-glucuronidase (GUS) reporter gene under the control of either the NtODC-1 or NtODC-2 gene promoter revealed that expression of the NtODC-1::GUS transgene was highly induced (8-fold) by treatment with MeJA, whereas the NtODC-2::GUS transgene showed little MeJA induced GUS expression. Removal of auxin (AUX, 2,4-D) from the cell growth media led to an increase in NtODC-1 and NtODC-2 transcript levels, whereas high levels of 2,4-D repressed overall ODC gene expression and suppressed the MeJA-induced expression of NtODC-1. Deletion analysis identified an upstream region (−924 to −1424 bp relative to the start site of transcription) of the NtODC-1 promoter that confers MeJA-responsiveness. No similar region was identified in the NtODC-2 promoter. Sequence analysis revealed that the NtODC-1 promoter fragment contains both G-box and TGACG-motif elements similar to those found in other MeJA-responsive genes. Our findings are discussed in terms of potential factors mediating different phytohormone-activated signal transduction pathways in the formation of nicotine and related compounds in tobacco.