Minisymposium 14: Hormones II

Abs # 26004: PIN1 and PIN4, but not PIN2, auxin efflux carriers are mislocalized in flavonoid-deficient mutants

Presenter:	Peer, Wendy A, peerw@purdue.edu
Authors	Peer, Wendy A (A)   Bandyopadhyay, Anindita  (A)   Blakeslee, Joshua J (A)   Markham, Srinivas  (A)   Murphy, Angus S (A)
Affiliations:	(A): Purdue University

In earlier studies we demonstrated that aglycone flavonols are active compounds that can regulate enzyme activity. We also reported that auxin transport and elongation growth in some tissues were altered in the flavonoid-deficient, chalcone synthase, transparent testa, tt4 mutation, and that flavonoid precursor feeding with naringenin restored both auxin transport and flavonoid localization to wildtype (WT) levels. We also demonstrated that aglycone flavonoids are localized in regions of state transition: the cotyledonary node, the root-shoot transition zone, and the distal elongation zone (DEZ) / root tip. More recently, we found differences in root length and number of secondary roots in seedlings grown without sucrose when tt mutants were compared to WT. In mature plants, differences in inflorescence length and time to flowering were found to be light reversible in all of the tt mutants examined except tt4. Here, we report that auxin transport profiles are also altered in mutants of the early genes in the biosynthetic pathway: tt7, a flavone 3'-hydroxlase mutant that accumulates kaempferol, and tt3, a dihydroflavonol reductase mutant that accumulates excess quantities of kaempferol and quercetin. We hypothesized that these differences in auxin transport may be due to altered localization of auxin efflux carriers. Consistent with observed altered auxin transport profiles, the localization of the PIN proteins was altered in tt4, tt7, and tt3 when compared to WT. PIN1 is mislocalized in tt4 and altered in tt7 and tt3 root tips and DEZ. PIN2 localization in the root tip and DEZ in the mutants is similar to WT with subtle changes in tt7. PIN4 is mislocalized in the root tips and DEZ of tt4 and tt7, and altered in tt3 compared to WT. Treatment with the auxin transport inhibitors n-1-napthylphthalamic acid (NPA) and triiodic benzoic acid (TIBA) also alter PIN1 and PIN4 localization in the root tips and DEZ of the mutants. Flavonoid precursor feeding experiments restore WT patterns of PIN1 and PIN4 localization in tt4; however, aglycone flavonol feeding resulted in altered localizations. Although some of the effects noted can be attributed to alterations in auxin bias, the majority cannot. These data suggest that certain flavonol species are required for correct polar targeting of PINs to cell membranes and support our hypothesis that aglycone flavonols act as autocrine effectors.