Thiophene acetic acid induces an auxin response and modulates organogenesis and gene expression across diverse plant species

Phytohormone auxin plays critical roles in many aspects of plant growth and development. Considering the complexity of auxin response and cross-talk with other signaling pathways, identifying novel auxins can significantly broaden their applications. Our previous research identified thiophene-3-acetic acid (T3AA), a degradation product of the β-lactam antibiotic ticarcillin, as a potential auxin analog. In this study, we further investigated T3AA and demonstrated its capacity to elicit an auxin response in Arabidopsis and tobacco. T3AA was found to negatively affect primary root length in Arabidopsis, while promoting a dose-dependent increase in the number of lateral roots and root hairs. Additionally, T3AA positively influenced gravitropic responses in Arabidopsis root at lower concentrations. The presence of a polar auxin transport inhibitor, N-1-naphthylphthalamic acid, led to an increased number of root hairs in T3AA-treated Arabidopsis seedlings. Furthermore, the expression levels of several early auxin-responsive genes in Arabidopsis were upregulated in the presence of T3AA. T3AA positively influenced shoot regeneration from tobacco leaf explants in vitro. Treatment with exogenous T3AA was shown to induce the expression of reporter gene under the control of auxin-response elements in transgenic tobacco. Overall, our findings affirm that T3AA can effectively induce auxin responses and significantly impact plant growth and development in different plant species.