RT Journal Article
SR Electronic
T1 A Small-Molecule Screen Identifies <span class="sc">l</span>-Kynurenine as a Competitive Inhibitor of TAA1/TAR Activity in Ethylene-Directed Auxin Biosynthesis and Root Growth in <em>Arabidopsis</em>
JF The Plant Cell
JO Plant Cell
FD American Society of Plant Biologists
SP 3944
OP 3960
DO 10.1105/tpc.111.089029
VO 23
IS 11
A1 He, Wenrong
A1 Brumos, Javier
A1 Li, Hongjiang
A1 Ji, Yusi
A1 Ke, Meng
A1 Gong, Xinqi
A1 Zeng, Qinglong
A1 Li, Wenyang
A1 Zhang, Xinyan
A1 An, Fengying
A1 Wen, Xing
A1 Li, Pengpeng
A1 Chu, Jinfang
A1 Sun, Xiaohong
A1 Yan, Cunyu
A1 Yan, Nieng
A1 Xie, De-Yu
A1 Raikhel, Natasha
A1 Yang, Zhenbiao
A1 Stepanova, Anna N.
A1 Alonso, Jose M.
A1 Guo, Hongwei
YR 2011
UL http://www.plantcell.org/content/23/11/3944.abstract
AB The interactions between phytohormones are crucial for plants to adapt to complex environmental changes. One example is the ethylene-regulated local auxin biosynthesis in roots, which partly contributes to ethylene-directed root development and gravitropism. Using a chemical biology approach, we identified a small molecule, l-kynurenine (Kyn), which effectively inhibited ethylene responses in Arabidopsis thaliana root tissues. Kyn application repressed nuclear accumulation of the ETHYLENE INSENSITIVE3 (EIN3) transcription factor. Moreover, Kyn application decreased ethylene-induced auxin biosynthesis in roots, and TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1/TRYPTOPHAN AMINOTRANSFERASE RELATEDs (TAA1/TARs), the key enzymes in the indole-3-pyruvic acid pathway of auxin biosynthesis, were identified as the molecular targets of Kyn. Further biochemical and phenotypic analyses revealed that Kyn, being an alternate substrate, competitively inhibits TAA1/TAR activity, and Kyn treatment mimicked the loss of TAA1/TAR functions. Molecular modeling and sequence alignments suggested that Kyn effectively and selectively binds to the substrate pocket of TAA1/TAR proteins but not those of other families of aminotransferases. To elucidate the destabilizing effect of Kyn on EIN3, we further found that auxin enhanced EIN3 nuclear accumulation in an EIN3 BINDING F-BOX PROTEIN1 (EBF1)/EBF2-dependent manner, suggesting the existence of a positive feedback loop between auxin biosynthesis and ethylene signaling. Thus, our study not only reveals a new level of interactions between ethylene and auxin pathways but also offers an efficient method to explore and exploit TAA1/TAR-dependent auxin biosynthesis.