# Novel auxin signaling components and pathways.

> **NIH NIH R35** · UNIVERSITY OF CALIFORNIA, SAN DIEGO · 2022 · $395,000

## Abstract

Project Summary
The plant hormone auxin regulates virtually all aspects of plant growth and development. We and others have
demonstrated that auxin promotes degradation of transcriptional repressors called Aux/IAA proteins, via a
family E3 ligases called SCFTIR1/AFB. Auxin is perceived by a co-receptor consisting of a TIR1/AFB protein, the F-
box subunit of the E3, and the Aux/IAA protein. The formation of this complex promotes degradation of the
Aux/IAA protein and transcription by ARF transcription factors. Although this basic pathway is well
established, it is not clear how auxin regulates such a wide range of developmental and physiological processes.
Currently in the second year of our RO1 grant, we are investigating this broad question using two
complementary genetic systems; the flowering plant Arabidopsis thaliana, and the basal land plant
Physcomitrella patens. Our focus has been on the function of the TIR1/AFB proteins, regulation of Aux/IAA
level, and the architecture of the auxin signaling network. We recently demonstrated that 5 of the 6 member
TIR1/AFB family in Arabidopsis act in an overlapping fashion. The 6th member, AFB1, functions in a novel
transcription-independent auxin response pathway. Further, our recent ChIPseq experiments indicate that
TIR1/AFB proteins (excluding AFB1) are recruited by auxin to chromatin adjacent to auxin-regulated genes.
We speculate that this mechanism permits rapid de-repression of auxin responsive genes. We also made
significant advances in our understanding of Aux/IAA proteins and their regulation. We recently discovered
that Aux/IAA are substrates of E3 ligases called CRL3-BPM, in addition to SCFTIR1/AFB. The BPMs are orthologs
of the human SPOP proteins. In addition, we showed that the Aux/IAA genes are regulatory nodes that
integrate environmental signals with the auxin gene regulatory network. For example, we have shown that
certain Aux/IAA proteins confer drought tolerance by regulating the levels of secondary products called
glucosinolates. These compounds promote stomatal closure and drought tolerance. In the next 5 years we will
continue to investigate the molecular basis of auxin signaling and to characterize the auxin-based regulatory
networks that control plant growth and development. We are very interested in the novel rapid auxin response
pathway and its role in growth. We will also investigate the regulation of Aux/IAA levels by both SCFTIR1/AFB
and CRL3-BPM. One of our long-term goals is understand the specificity of the AFB, Aux/IAA, and ARF
proteins in collaboration with Joe Ecker's lab at the Salk Institute. This effort will include the investigation of
AFB recruitment to chromatin. These studies address a number of key issues in cellular regulation and will
have important implications for human health.

## Key facts

- **NIH application ID:** 10398201
- **Project number:** 5R35GM141892-02
- **Recipient organization:** UNIVERSITY OF CALIFORNIA, SAN DIEGO
- **Principal Investigator:** MARK A ESTELLE
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $395,000
- **Award type:** 5
- **Project period:** 2021-05-01 → 2026-04-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10398201

## Citation

> US National Institutes of Health, RePORTER application 10398201, Novel auxin signaling components and pathways. (5R35GM141892-02). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10398201. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*