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Abstract Detail


Auxin Biology

Srinivas, Makam [1], Li, Nanbing [2], Legas, Sheenalay [2], Sanjai, Deepti [3], Peer, Wendy [3], Murphy, Angus [3].

Arabidopsis APP1 is a rate limiting component of Auxin signalling required for activation of DR5-like Auxin response elements.

Arabidopsis APP1 is a membrane-associated soluble aminopeptidase with activity against N-terminal Arg>> Pro>Leu>Tyr>X-Pro>Trp residues. APP1 is a single copy gene and was originally isolated by its weak affinity for the auxin transport inhibitor 1-Naphthylphthalamic acid (NPA). Enzymatic activity of APP1 is partially inhibited by NPA and the similar auxin transport inhibitor DCPFA although activation is seen at higher NPA concentrations. Mutations in APP1 result in drastically reduced growth. Overexpression results in increased growth, enhanced lateral root formation, and decreased seed set. Treatment of app1 with auxin does not restore growth. Treatment of APP1 overexpressors with NPA restores wild type growth. APP1 expression is induced by auxin, wounding, and jasmonic acid. However, IAA treatment upto 500nM decreases APP1 protein levels indicating enhanced turnover but increases then after upto 5μM tested. APP1 exhibits affinity for WPP peptide motifs and binds diprolyl motifs in AUX-IAA proteins with relatively high affinity in vivo and in vitro at different auxin gradients for IAA1 and IAA7. Binding severly decreases when iaa7 diprolyl mutant peptides are substituted in the pulldowns but is auxin independent when the iaa1 mutant used. DR5:GUS activity and transcription are barely detectable in the app1 knockout mutant background, even after auxin treatment analogous to DR5 Juglone treatment. Juglone and MG132 enhances AtAPP1 interaction in the pull down assays. Increase APP1 activity results in ectopic DR5:GUS expression in the enhanced Tyr-AP activity atapp1-5 mutant background. However, app1 mutants exhibit no detectable alterations in auxin accumulation or transport. These results suggest that activation of DR5 like auxin response elements by Auxin Response Factors requires APP1-dependent degradation of Aux-IAA repressor proteins. These results suggest that APP1 functions as an activator of AUX-IAA-dependent signalling and auxin-dependent AUX-IAA degradation, either by enhancing IAA-TIR1/AFB binding or enhancing SCF-TIR access to AUX-IAA proteins.


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1 - Purdue University, Department of Horticulture and Landscape Architecture, 625, Agricultural Mall drive, Purdue University, West Lafayette, IN, 47907, USA
2 - University of Texas Pan-American, Biology Department
3 - Purdue University, Department of Horticulture and Landscape Architecture

Keywords:
auxin
AtAPP1
DR5-GUS
Signaling
AUX-IAA.

Presentation Type: ASPB Minisymposium
Session: M20
Location: Continental B/Hilton
Date: Tuesday, July 10th, 2007
Time: 3:45 PM
Number: M20002
Abstract ID:694


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