Receptors auxin

Kim, Y. S., D. H. Kim, and ]. Jung. Isolation of a novel auxin receptor from soluble fractions of rice (Oryza sativa L.) shoots. FEBS Lett 1998 438(3) ... 

Amid an ever clearer picture of auxin action, the auxin receptor remained a conspicuous omission from signaling models. Early biochemical efforts to isolate auxin receptors identified AUXIN-BINDING PROTEIN1 (ABP1).184,185 However, the majority of ABP1 localizes to the endoplasmic reticulum where the pH is too high for auxin binding. Furthermore, embryo-lethal null mutants and the lack of weak mutant alleles complicated detailed analysis. 

Auxins are synthesized in apical buds (at the tip) of growing shoots. They stimulate growth of the main shoot and inhibit lateral shoot development. A class of auxin-binding membrane proteins may represent auxin receptors. Auxin action involves pumping protons out of the cell, possibly in conjunction with a membrane ATPase. 

Auxin receptor proteins 2-Hydroxy-3,5-diiodo- Epoxy-activated Sepharose 6B 197... 

The auxin receptor has also been conceived as complementary to the lAA molecule in the extended planar conformation (Figs. 2 and 3C) [13]. The site consists of a carboxyl... 

Fig. 2. Model of the auxin receptor adapted from Katekar (13] and the way in which selected molecules would engage the site.

B. Phylogenetic tree of TIRl auxin receptor gene family in Arahidopsis. 

Auxins are one of the five major classes of plant-produced hormones that affect plant growth including bud formation and root initiation (see http //en.wikipedia. org/wiki/Plant hormone Auxins), lndole-3-acetic acid is the most common auxin found in plants. Although the small amounts produced internally have the desired effects, auxins are toxic to plants in larger amounts. The nefarious weed-control products 2,4-D and 2,4,5-T target the auxin receptor but bear little resemblance to the natural ligand. Other man-made auxins such as 1-naphthaleneacetic acid and indole-3-butyric acid are used, not to kill weeds, but to stimulate root production in cuttings taken from the parent plant (Scheme 6). 

Scheme 6 Herbicides that target the auxin receptor...

D-treated cells transcribed the mRNAs complementary to the seven cDNA clones only nuclei from water treated-cells gave no hybridization signal [17]. Therefore, these nuclei provide an excellent system with which transacting factors that may play a role in auxin-induced gene expression can be analyzed (i.e. the soluble auxin receptor [10, 15]). 

The next step in the perception-transduction mechanism of auxin should be more specific. We plan to use the reinitiating nuclei from tobacco in reconstitution experiments with partially purified auxin-binding protein. We have shown in vivo that several genes are specifically induced by auxin. We hope to be able to show the same induction in vitro by addition of auxin-receptor complex to nuclei isolated from auxin-starved cells, where these genes are normally not expressed. 

This approach, i.e. attacking the problem of auxin perception and transduction from both mRNA and auxin receptor sides, will give us a better understanding of the events that take place between the entry of auxin into a cell, and cell division, some 30 h later. 

Reliable and reproducible procedures are needed to purify auxin receptor protein for antibody production and for further biochemical characterization. Two auxin affinity methods have been reported [11,17], but such methods have yielded indifferent results in our hands [22]. This communication describes auxin receptor purification using commercially available chromatographic materials and the initial characterization of monoclonal and polyclonal antibodies produced against the resulting preparations. 

Polyclonal antiserum was produced by immunization of a single rabbit with native PAGE gel slices containing pure auxin receptor. 

Fig. 2. Immunoblots of post-DEAE maize membrane extracts using different dilutions of rabbit pre-immune or anti-auxin receptor serum...

Fig. 3. Effect of rabbit pre-immune (o-o) or anti-auxin receptor serum (x-x) on saturable f C]...

---