Characterization of the IBR5-PAD1 interaction in Arabidopsis auxin response




Siepert, Nicholas C.

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Many plant hormones utilize the ubiquitin-proteasome system (UPS) to modulate the expression of specific genes involved in various developmental processes as well as responses to environmental stress. In this process the target proteins are polyubiquitinated by a multi-subunit E3 ubiquitin ligase complex, essentially tagging the target proteins for degradation by the 26S proteasome. One specific type of E3 ligase, the SKP1-CULLIN1-F-BOX protein (SCF) complex, is utilized by several plant hormones to ubiquitinate target proteins. This process is highly specific and requires multiple levels of regulation which are not fully understood. Recent studies have shown that the INDOLE-3-BUTYRIC ACID RESPONSE5 (IBR5) gene, which encodes a dual specificity phosphatase, plays an important role in the auxin signaling pathway. Previous studies suggest that IBR5 negatively regulates Aux/IAA repressor protein degradation. This research identifies and characterizes a novel interaction between IBR5 and PAD1, a subunit of the 20S core of the proteasome. The interaction between IBR5 and PAD1 was confirmed in vitro and in vivo. Additionally, specific domains or regions of each protein were identified to be crucial for this interaction. Similar to ibr5 mutants, pad1 and pad2 displayed auxin-resistant phenotypes. Furthermore, the pad1 mutation partially rescued the AXR3NT-GUS destabilization in ibr5-4. Taken together, these findings suggest that the interaction between IBR5 and PAD1 may play a role in the regulation of auxin signaling and the UPS.



Auxin, Ubiquitin Proteasome System, 26S Proteasome


Siepert, N. C. (2017). <i>Characterization of the IBR5-PAD1 interaction in Arabidopsis auxin response</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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