Defining the selectivity of processes along the auxin response chain: a study using auxin analogues

Abstract

Summary The mode of action of auxin is based on its non‐uniform distribution within tissues and organs. Despite the wide use of several auxin analogues in research and agriculture, little is known about the specificity of different auxin‐related transport and signalling processes towards these compounds. Using seedlings of Arabidopsis thaliana and suspension‐cultured cells of Nicotiana tabacum (BY‐2), the physiological activity of several auxin analogues was investigated, together with their capacity to induce auxin‐dependent gene expression, to inhibit endocytosis and to be transported across the plasma membrane. This study shows that the specificity criteria for different auxin‐related processes vary widely. Notably, the special behaviour of some synthetic auxin analogues suggests that they might be useful tools in investigations of the molecular mechanism of auxin action. Thus, due to their differential stimulatory effects on DR5 expression, indole‐3‐propionic (IPA) and 2,4,5‐trichlorophenoxy acetic (2,4,5‐T) acids can serve in studies of TRANSPORT INHIBITOR RESPONSE 1/AUXIN SIGNALLING F‐BOX (TIR1/AFB)‐mediated auxin signalling, and 5‐fluoroindole‐3‐acetic acid (5‐F‐IAA) can help to discriminate between transcriptional and non‐transcriptional pathways of auxin signalling. The results demonstrate that the major determinants for the auxin‐like physiological potential of a particular compound are very complex and involve its chemical and metabolic stability, its ability to distribute in tissues in a polar manner and its activity towards auxin signalling machinery.

Defining Binding Efficiency and Specificity of Auxins for SCFTIR1/AFB-Aux/IAA Co-receptor Complex Formation

“…However, our receptor binding Efficiency ranking agrees well with previous systems, including those based only on biological activity (Supplementary Table S2) and the recent compilation linking tolerance to, e.g. , 2,4-D and 2,4,5-T with receptor selectivity, 29 adding mechanistic detail.…”

Regulation of Auxin Homeostasis and Gradients in Arabidopsis Roots through the Formation of the Indole-3-Acetic Acid Catabolite 2-Oxindole-3-Acetic Acid

“…Our data also showed that oxIAA did not interfere with the accumulation in cells of 2,4-D and NAA, which are known to be good substrates for the plasma membrane-located auxin carriers (Delbarre et al, 1996;Petrášek et al, 2006;Simon et al, 2013). This indicates that oxIAA is not transported via the auxin influx or efflux carriers (Figure 8).…”

Relative Contribution of PIN-Containing Secretory Vesicles and Plasma Membrane PINs to the Directed Auxin Transport: Theoretical Estimation

“…Moreover, SV localization of a member of the AGCVIII kinase family, the action of which is required for PIN activity [30], has not been reported, arguing that PINs in the SVs are possibly inactive [13]. An additional argument that PINs are active at the PM is that increasing PINs incidence at the cell surface, e.g., by inhibiting their endocytosis leads to increased auxin efflux [31,32]. Overall, methods for separate measurement or perturbation of parameters in Equations (48) and (49) are needed to unambiguously distinguish between vesicular-mediated and PM-mediated auxin fluxes.…”