Identification of a novel marker for auxin and ethylene cross-talk from tobacco seedlings

A novel early-response auxin-regulated gene, here termed Nt-AER (Auxin and Ethylene Regulated), was identified from a cDNA library prepared from auxin-treated tobacco (Nicotiana tabacum cv. Xanthi) seedlings. Comparison with sequence databases places Nt-AER in a family of transferase enzymes. Nt-AER was detected in a number of tobacco tissues with the exception of young leaves. In tobacco seedlings, Nt-AER is specifically up-regulated by auxins, but not their inactive analogues. A number of other plant growth regulators were tested of which the ethylene precursor ACC also induced Nt-AER accumulation. Steady-state levels of Nt-AER were relatively high in dark-grown tobacco seedlings but fell rapidly upon exposure to light and the possible role of ethylene in this response is discussed. Nt-AER was found to be rapidly induced following NAA or ACC treatment and maximum accumulation was detected for concentrations above 1 μM. Whilst ACC failed to induce Nt-AER in seedlings of transgenic ethylene insensitive tobacco, a response to NAA was retained. This suggests that Nt-AER is regulated by separable signalling pathways and not only by auxin-induced ethylene biosynthesis. As such, Nt-AER represents a novel marker for auxin and ethylene cross-talk.