Auxin efflux

Another area in which Arabidopsis genetics is proving to be useful is the study of the proposed role of flavonoids in regulating auxin transport. Several years ago, Jacobs and Rubery published the first evidence that flavonoids could specifically compete with naphthylphthalamic acid for binding to the auxin efflux carrier in etiolated zucchini hypocotyls.35 This finding was somewhat controversial, however, and no additional evidence for the connection between flavonoids and auxin transport was reported for some time. Brown et al. have now used Arabidopsis flavonoid mutants to generate new evidence in support of a role for flavonoids in the regulation of polar auxin movement.6 These experiments took... 

Bouchard R, Badly A, Blakeslee JJ, Oehring SC, Vincenzetti V, Lee OR, Paponov I, Palme K, Mancuso S, Murphy AS, Schulz B, Geisler M. 2006. Immunophilin-like TWISTED DWARF1 modulates auxin efflux activities of Arabidopsis P-glycopro-teins. J Biol Chem 281 30603-30612. 

Friml J, Yang X, Michniewicz M, Weijers D, Quint A, Tietz O, Benjamins R, Ouwerkerk PB, Ljung K, Sandberg G, Hooykaas PJ, Palme K, Offringa R. 2004. A PINOID-dependent binary switch in apical-basal PIN polar targeting directs auxin efflux. Science 306 862-865. 

Peer WA, Bandyopadhyay A, Blakeslee JJ, Makam SN, Chen RJ, Masson PH, Murphy AS. 2004. Variation in expression and protein localization of the PIN family of auxin efflux facilitator proteins in flavonoids mutants with altered auxin transport in Arabidopsis thaliana. Plant Cell 16 1898-1911. 

Fig. 7.2 A-E. Interactions of lAA with ABA, GA, TIBA, and zeatin (ZEA), alone or in combination, as evidenced by effects upon the wavelike pattern of auxin efflux from the basal ends of successive 6-mm-long pine stem sections. Protocol as in Fig. 7.1. Test substances were applied for 100 min prior to sectioning and positioning for 10-min auxin basal efflux period. Test substances were applied apically only in A, C, D, and E, but both apically (a) and basally (b) in B. Controls had no exposure to exogenous substances. (A, B, C, and D adapted from Wod-ziCKi and Wodzicki 1981 E from WoDZiCKi et al. 1979)...

Application of zeatin in agar gels to the apical ends of stem segments before sectioning them produced some increase of the auxin efflux. The most interesting action of both cytokinin and gibberellic acid, however, was prevention of the depressive effect of abscisic acid upon the wave-like pattern of the basipetal efflux of auxin (Fig. 7.2 C, D). 

Bouchard, R., BaiUy, A., Blakeslee, J.J. et al. (2006). Immunophilin-like TWISTED DWARFl modulates auxin efflux activities of Arabidopsis P-glycoproteins. Journal of Biological Chemistry, 281, 30603-30612. 

Steinmann, T., Geldner, N., Grebe, M. et al. (1999). Coordinated polar localization of auxin efflux carrier PINl by GNOM ARF GEE Science, 286,316-318. 

Fig. 22.3 Consensus effects of Spd and Spm on auxin metabolism and signaling cascade. Description is same as in legends to Fig. 22.1. AFB2 auxin signaling F-box protein 2, ARFs auxin response factors, Awc/IAA indole-3-acetic acid inducible (members of Aux/IAA protein family), AuxRE auxin response cu-elements, GH3 lAA-amido synthetase, lAMTl lAA carboxyl methyl transferase 1, ILL4 lAA amidohydrolase, LAX3 like AUXl 3, PGP 10 P-glycoprotein 10 (auxin efflux carrier), PINl PIN-formed 1, PINS PIN-formed 5, TIRl transport inhibitor response 1, YUC YUCCA...

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