title: ABA-dependent inhibition of the ubiquitin proteasome system during germination at high temperature in Arabidopsis.
abstract: During germination, endogenous and environmental factors trigger changes in the transcriptome, translatome and proteome to break dormancy. In Arabidopsis thaliana, the ubiquitin proteasome system (UPS) degrades proteins that promote dormancy to allow germination. While research on the UPS has focused on the identification of proteasomal substrates, little information is known about the regulation of its activity. Here we characterized the activity of the UPS during dormancy release and maintenance by monitoring protein ubiquitination and degradation of two proteasomal substrates: Suc-LLVY-AMC, a well characterized synthetic substrate, and FUSCA3 (FUS3), a dormancy-promoting transcription factor degraded by the 26S proteasome. Our data indicate that proteasome activity and protein ubiquitination increase during imbibition at optimal temperature (21°C), and are required for seed germination. However, abscisic acid (ABA) and supraoptimal temperature (32°C) inhibit germination by dampening both protein ubiquitination and proteasome activity. Inhibition of UPS function by high temperature is reduced by the ABA biosynthesis inhibitor, fluridone, and in ABA biosynthetic mutants, suggesting that it is ABA dependent. Accordingly, inhibition of FUS3 degradation at 32°C is also dependent on ABA. Native gels show that inhibition of proteasome activity is caused by interference with the 26S/30S ratio as well as free 19S and 20S levels, impacting the proteasome degradation cycle. Transfer experiments show that ABA-mediated inhibition of proteasome activity at 21°C is restricted to the first 2 days of germination, a time window corresponding to seed sensitivity to environmental and ABA-mediated growth inhibition. Our data show that ABA and high temperature inhibit germination under unfavourable growth conditions by repressing the UPS.
authors: Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.|Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada.
authors: Rex Shun
authors: RS
authors: Chiu
authors: Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.
authors: Shiyue
authors: S
authors: Pan
authors: Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.|Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada.
authors: Rongmin
authors: R
authors: Zhao
authors: Department of Biological Sciences, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, M1C 1A4, Canada.|Department of Cell and Systems Biology, University of Toronto, 25 Harbord Street, Toronto, ON, M5S 3G5, Canada.
authors: Sonia
authors: S
authors: Gazzarrini
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018525:Germination / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C502726:FUSCA3 protein, Arabidopsis; D014157:Transcription Factors; D025801:Ubiquitin; D000040:Abscisic Acid; D046988:Proteasome Endopeptidase Complex
keywords: FUSCA3; abscisic acid; dormancy; germination; high temperature; proteasome; protein degradation; thermoinhibition; ubiquitin proteasome system