Strader, Lucia , Monroe-Augustus, Melanie , Bartel, Bonnie .
IBR5, a putative dual-specificity protein phosphatase, affects auxin response independently of TIR1.
The phytohormone auxin affects many aspects of plant growth and development, influencing cell division, elongation, and differentiation at the cellular level and affecting apical dominance, lateral root formation, and tropisms at the whole-plant level. Mutations in IBR5 (INDOLE 3-BUTYRIC ACID RESPONSE5), encoding a putative dual-specificity protein phosphatase, confer decreased sensitivity to auxins and auxinic compounds (Monroe-Augustus et al., 2003, Plant Cell 15:2979). In an effort to understand how IBR5 modulates auxin signaling, we evaluated effects of the ibr5 mutation on molecular auxin responses. Levels of the auxin-inducible transcripts IAA1 and IAA2 were reduced in ibr5 relative to wild type, suggesting that IBR5 acts upstream of the transcriptional regulation of these genes. Repression of IAA1 and IAA2 can be relieved by the TIR1-mediated 26S-proteasomal degradation of AUX/IAA repressor proteins. However, we found that the AUX/IAA protein AXR3, which is stabilized in several other auxin response mutants, was not stabilized in ibr5. This result suggests that IBR5 affects auxin-responsive transcription by a method other than promoting AUX/IAA degradation. We used double mutant analysis to determine how other auxin response players genetically interact with ibr5. The double mutants ibr5 tir1, ibr5 aux1, and ibr5 axr1 all exhibit additive auxin resistance, suggesting that IBR5 acts in a separate pathway from TIR1, AUX1, or AXR1. Overall, our results suggest that IBR5 modulates auxin responsive transcription by an unknown mechanism. We are conducting an ibr5 modifier screen to further elucidate this process. (This research is supported by the NIH.)
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1 - Rice University, Biochemistry & Cell Biology, 6100 S. Main St - MS140
Rice University, Rice University, Houston, TX, 77005, United States
2 - Rice University, Biochemistry & Cell Biology
Presentation Type: ASPB Minisymposium
Location: Continental B/Hilton
Date: Tuesday, July 10th, 2007
Time: 3:20 PM