Journal
PLANT AND CELL PHYSIOLOGY
Volume 55, Issue 8, Pages 1450-1459Publisher
OXFORD UNIV PRESS
DOI: 10.1093/pcp/pcu077
Keywords
AFB; Arabidopsis thaliana; Aux/IAA; Auxin; Sensitivity; TIR1
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Funding
- Japan Society for the Promotion of Science [25291060]
- Japan Society for the Promotion of Science (JSPS) [231933]
- Ministry of Education, Culture, Sports, Science, and Technology, Japan [25113006, 19060005]
- Grants-in-Aid for Scientific Research [25113006, 19060005] Funding Source: KAKEN
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Auxin plays a key role in regulation of almost all processes of plant growth and development. Different physiological processes are regulated by different ranges of auxin concentrations; however, the underlying mechanisms creating these differences are largely unknown. The first step of auxin signaling is auxin-dependent interaction of an auxin receptor with transcriptional co-repressors (Aux/IAA), which leads to Aux/IAA degradation. Arabidopsis has six homologous auxin receptors (TIR1 and five AFBs), 29 Aux/IAA proteins and two types of active auxins, IAA and phenylacetic acid (PAA). Therefore, a large number of possible combinations between these three factors may contribute to the creation of complex auxin responses. Using a yeast heterologous reconstitution system, we investigated auxin-dependent degradation of all Arabidopsis Aux/IAAs in combination with every TIR or AFB receptor component. We found that TIR1 and AFB2 were effective in mediating Aux/IAA degradation. We confirmed that the Aux/IAA domain II, which binds TIR1, is essential for degradation. IAA and other natural auxins, 4-chloroindole-3-acetic acid (4-Cl-IAA) and PAA, induced Aux/IAA degradation; and IAA and 4-Cl-IAA had higher activity than PAA. Effective auxin concentrations for Aux/IAA degradation depended on both Aux/IAAs and TIR1 or AFB2 receptors, which is consistent with the Aux/IAA-TIR1/AFB co-receptor concept.
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