Editors' ChoicePlant biology

Regulators of Auxin Transport

Science's STKE  19 Jun 2001:
Vol. 2001, Issue 87, pp. tw8
DOI: 10.1126/stke.2001.87.tw8

Auxin is a plant hormone important for elongation and differentiation of various plant tissues. The effects of auxin are spatially restricted to a particular direction by polar flow of auxin through localized efflux and influx transporters. Zhong and Ye show that the homeodomain leucine zipper protein encoded by the IFL1 gene regulates the expression of two putative auxin efflux carrier genes, PIN3 and PIN4. Plants with mutations in the ifl1gene mutant had lower levels of auxin transport in the affected tissues compared with wild-type plants, supporting the conclusion that decreased expression of PIN3 and PIN4 contributes to decrease auxin signaling. Pharmacological inhibitors of auxin efflux mimicked the phenotypes observed in the ifl1 mutant plants, confirming the interaction of IFL1 with auxin signaling. A second regulatory mechanism described in a separate report was at the level of the activity of the efflux transporter. Brown et al. show that flavonoids are endogenous regulators of auxin efflux transporters by analyzing the phenotypes and transporter activity in plants with mutations in the flavonoid biosynthetic pathway. These plants had phenotypes consistent with excessive auxin signaling and showed enhanced auxin transport. Thus, this work provides evidence in vivo for the activity of flavonoids as endogenous inhibitors of auxin efflux, confirming data from in vitro studies and results from exogenous application of flavonoid compounds showing that flavonoids inhibited auxin efflux.

R. Zhong, Z.-H. Ye, Alteration of auxin polar transport in the Arabidopsis ifl1 mutants. Plant Physiol. 126, 549-563 (2001). [Abstract] [Full Text]

D. E. Brown, A. M. Rashotte, A. S. Murphy, J. Normanly, B. W. Tague, W. A. Peer, L. Taiz, G. K. Muday, Flavonoids act as negative regulators of auxin transport in vivo in Arabidopsis. Plant Physiol. 126, 524-535 (2001). [Abstract] [Full Text]