Fig. 1.

Fine-tuning the IPyA pathway in Arabidopsis. The two-step IPyA pathway is the predominant auxin biosynthesis pathway in Arabidopsis. Conversion of tryptophan to IAA (auxin) consists of two steps: TAA conversion of Trp to IPyA, followed by YUC conversion of IPyA to IAA. Fine-tuned IAA production in response to environmental stimuli, as seen in response to elevated temperature or light, is critical for developmental response to these stimuli. In the IPyA pathway for IAA biosynthesis, these environmental stimuli trigger PIF4-mediated transcriptional regulation of enzymes involved in modification or biosynthesis of IAA.