Broadening the roles of UDP‐glycosyltransferases in auxin homeostasis and plant development

AbstractInactivation of the phytohormone auxin plays important roles in plant development, and several enzymes have been implicated in auxin inactivation. In this study, we show that the predominant natural auxin, indole-3-acetic acid (IAA), is mainly inactivated via the GH3-ILR1-DAO pathway. IAA is first converted to IAA-amino acid conjugates by GH3 IAA-amidosynthetases. The IAA-amino acid conjugates IAA-aspartate (IAA-Asp) and IAA-glutamate (IAA-Glu) are storage forms of IAA and can be converted back to IAA by ILR1/ILL amidohydrolases. We further show that DAO1 dioxygenase irreversibly oxidizes IAA-Asp and IAA-Glu into 2-oxindole-3-acetic acid-aspartate (oxIAA-Asp) and oxIAA-Glu, which are subsequently hydrolyzed by ILR1 to release inactive oxIAA. This work established a complete pathway for the oxidative inactivation of auxin and defines the roles played by auxin homeostasis in plant development.

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MicroRNAs Regulate Auxin Homeostasis and Plant Development

The Plant Cell ◽

10.1105/tpc.105.033159 ◽

2005 ◽

Vol 17 (5) ◽

pp. 1335-1338 ◽

Cited By ~ 18

Author(s):

Nancy A. Eckardt

Keyword(s):

Plant Development ◽

Auxin Homeostasis

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The 5′-3′ Exoribonuclease XRN4 Regulates Auxin Response via the Degradation of Auxin Receptor Transcripts

Genes ◽

10.3390/genes9120638 ◽

2018 ◽

Vol 9 (12) ◽

pp. 638 ◽

Cited By ~ 1

Author(s):

David Windels ◽

Etienne Bucher

Keyword(s):

Plant Development ◽

Transcriptional Repressors ◽

Auxin Response ◽

Auxin Receptor ◽

Developmental Programs ◽

Developmental Defects ◽

Auxin Homeostasis ◽

New Targets ◽

Specific Degradation

Auxin is a major hormone which plays crucial roles in instructing virtually all developmental programs of plants. Its signaling depends primarily on its perception by four partially redundant receptors of the TIR1/AFB2 clade (TAARs), which subsequently mediate the specific degradation of AUX/IAA transcriptional repressors to modulate the expression of primary auxin-responsive genes. Auxin homeostasis depends on complex regulations at the level of synthesis, conjugation, and transport. However, the mechanisms and principles involved in the homeostasis of its signaling are just starting to emerge. We report that xrn4 mutants exhibit pleiotropic developmental defects and strong auxin hypersensitivity phenotypes. We provide compelling evidences that these phenotypes are directly caused by improper regulation of TAAR transcript degradation. We show that the cytoplasmic 5′-3′ exoribonuclease XRN4 is required for auxin response. Thus, our work identifies new targets of XRN4 and a new level of regulation for TAAR transcripts important for auxin response and for plant development.

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Chemical inhibition of auxin inactivation pathway uncovers the metabolic turnover of auxin homeostasis

10.1101/2021.10.12.464031 ◽

2021 ◽

Author(s):

Kosuke Fukui ◽

Kazushi Arai ◽

Yuka Tanaka ◽

Yuki Aoi ◽

Vandna Kukshal ◽

...

Keyword(s):

Acetic Acid ◽

Amino Acid ◽

Plant Development ◽

In Planta ◽

Auxin Homeostasis ◽

Auxin Concentration ◽

Auxin Synthesis ◽

Chemical Inhibition ◽

Conjugating Enzymes ◽

Indole 3 Acetic Acid

The phytohormone auxin, specifically indole-3-acetic acid (IAA) plays a prominent role in plant development. Cellular auxin concentration is coordinately regulated by auxin synthesis, transport, and inactivation to maintain auxin homeostasis; however, the physiological contribution of auxin inactivation to auxin homeostasis has remained elusive. The GH3 genes encode auxin amino acid conjugating enzymes that perform a central role in auxin inactivation. The chemical inhibition of GH3s in planta is challenging because the inhibition of GH3 enzymes leads to IAA overaccumulation that rapidly induces GH3 expression. Here, we developed a potent GH3 inhibitor, designated as kakeimide (KKI), that selectively targets auxin-conjugating GH3s. Chemical knockdown of the auxin inactivation pathway demonstrates that auxin turnover is very rapid (about 10 min), indicating auxin biosynthesis and inactivation dynamically regulate auxin homeostasis.

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ER-Localized PIN Carriers: Regulators of Intracellular Auxin Homeostasis

Plants ◽

10.3390/plants9111527 ◽

2020 ◽

Vol 9 (11) ◽

pp. 1527

Author(s):

Nayyer Abdollahi Sisi ◽

Kamil Růžička

Keyword(s):

Endoplasmic Reticulum ◽

Plasma Membrane ◽

Subcellular Localization ◽

Plant Development ◽

Current Knowledge ◽

Structural Features ◽

Structure Evolution ◽

Auxin Homeostasis ◽

Auxin Efflux Carriers ◽

Hydrophilic Loop

The proper distribution of the hormone auxin is essential for plant development. It is channeled by auxin efflux carriers of the PIN family, typically asymmetrically located on the plasma membrane (PM). Several studies demonstrated that some PIN transporters are also located at the endoplasmic reticulum (ER). From the PM-PINs, they differ in a shorter internal hydrophilic loop, which carries the most important structural features required for their subcellular localization, but their biological role is otherwise relatively poorly known. We discuss how ER-PINs take part in maintaining intracellular auxin homeostasis, possibly by modulating the internal levels of IAA; it seems that the exact identity of the metabolites downstream of ER-PINs is not entirely clear as well. We further review the current knowledge about their predicted structure, evolution and localization. Finally, we also summarize their role in plant development.

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