Nuclear accumulation of the ankyrin repeat protein ANK1 enhances the auxin-mediated transcription accomplished by the bZIP transcription factors BZI-1 and BZI-2.
The tobacco (Nicotiana tabacum) basic leucine zipper (bZIP) transcription factor BZI-1 has been implicated in auxin-mediated gene regulation. Yeast two-hybrid analysis has led to the identification of two BZI-1 protein interaction partners: the heterodimerizing bZIP factor BZI-2 and an ankyrin repeat domain protein, ANK1. Analysis in transgenic plants confirms that low levels of functional BZI-1, BZI-2 and ANK1 result in reduced auxin responses. This finding indicates that the three proteins act in the same functional context. The in vivo interaction of ANK1 and BZI-1 has been confirmed by protoplast two-hybrid analysis, as well as by bimolecular fluorescence complementation (BiFC) studies. Whereas YFP-BZI-1 has been found to be localized in the nucleus, YFP-ANK1 resides in the cytosol. Nevertheless, the inhibition of nuclear export with the inhibitor leptomycin B (LMB) and the co-expression with BZI-1, as well as treatment with auxin, results in the accumulation of YFP-ANK1 in the nucleus. Whereas BZI-1 is a weak activator, BZI-1/BZI-2 heterodimers efficiently support transcription. Importantly, conditions that lead to the accumulation of ANK1 in the nucleus, such as the expression of an ANK1 protein fused to a nuclear localization sequence (NLS) or auxin treatment, lead to a significant enhancement of BZI-1/BZI-2-mediated transcription. We therefore propose a mechanism in which the nuclear accumulation of ANK1 enhances BZI-1/BZI-2-mediated transcription in an auxin-dependent manner, presumably facilitated by protein-protein interaction. In summary, this study defines novel components in auxin-dependent signalling and transcriptional control.
Böttner
Stefan
S
Albrecht-von-Haller-Institut, Universität Göttingen, Untere Karspüle 2, D-37073 Göttingen, Germany.
Iven
Tim
T
Carsjens
Caroline S
CS
Dröge-Laser
Wolfgang
W
D021581:Active Transport, Cell Nucleus; D017089:Ankyrin Repeat; D017487:Ankyrins / Q000235:genetics / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D017487:Ankyrins; D050976:Basic-Leucine Zipper Transcription Factors; D007210:Indoleacetic Acids; D010940:Plant Proteins