# Mechanism of Auxin Action

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA, SAN DIEGO · 2020 · $307,125

## Abstract

Project Summary
 The plant hormone auxin is involved in virtually all aspects of plant growth and development. Over the
years we and others have demonstrated that auxin acts by stimulating the degradation of a family of
transcriptional repressors called the Aux/IAA proteins, through the action of the ubiquitin protein ligase
SCFTIR1/AFB. Although this basic pathway is well established, we still know very little about how auxin regulates
plant growth and development. Strikingly, auxin-regulated genes differ dramatically between cell types and
organs, consistent with the diverse roles of the hormone. The basis for this specificity is unknown. Similarly,
the activities of the Aux/IAA and ARF proteins are poorly characterized and the transcriptional networks
(GRNs) that mediate various auxin-regulated growth processes have not been defined. Finally, we know little
about how auxin signaling is integrated with other environmental and genetic signaling pathways.
 During the last grant period we demonstrated that the 6 members of the AFB family of F-box proteins act
in an additive fashion but may also have specific functions. In addition, our recent ChIPseq experiments
indicate that the AFB proteins are bound to chromatin adjacent to auxin-regulated genes and are recruited to
these sites by auxin. We speculate that the close association of SCFAFB with chromatin permits rapid de-
repression of auxin responsive genes. We also made significant advances in our understanding of the Aux/IAA
proteins and the architecture of the auxin signaling network. Our work shows that the Aux/IAA genes function
as regulatory nodes that integrate environmental signals with the auxin gene regulatory network. Most
exciting, we have shown that the DREB2-dependent but ABA-independent abiotic stress response pathway acts
through the Aux/IAAs to mediate drought tolerance. Further we demonstrate that this pathway regulates the
levels of secondary products called glucosinolates and that these compounds promote stomatal closure and
drought tolerance. These studies indicate that glucosinolates have previously unknown signaling properties.
 The long-term goals of this proposal are to determine the molecular basis of auxin signaling and to
characterize the auxin-based regulatory networks that control plant growth and development. Our specific
aims are to; 1) Investigate the role of the IAA5,6,19 protein in DREB2-mediated drought tolerance, 2)
Determine the mechanism of Aux/IAA-based transcriptional repression, 3) Explore the specificity of the AFB
and Aux/IAA proteins, and 4) Investigate recruitment of AFBs to chromatin. These studies address a number
of key issues in cellular regulation and will have important implications for human health. The ubiquitin
pathway and the SCFs in particular are involved in diverse disease processes including numerous cancers.
Because SCFTIR/AFB1 is one of the best-characterized E3 complexes in any organism, this work provides a unique
opportunity to adva...

## Key facts

- **NIH application ID:** 9851403
- **Project number:** 5R01GM043644-31
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN DIEGO
- **Principal Investigator:** MARK A ESTELLE
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $307,125
- **Award type:** 5
- **Project period:** 1989-08-01 → 2023-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9851403

## Citation

> US National Institutes of Health, RePORTER application 9851403, Mechanism of Auxin Action (5R01GM043644-31). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/9851403. Licensed CC0.

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