The Proteasome Stress Regulon Is Controlled by a Pair of NAC Transcription Factors in Arabidopsis

Abstract

Proteotoxic stress, which is generated by the accumulation of unfolded or aberrant proteins due to environmental or cellular perturbations, can be mitigated by several mechanisms, including activation of the unfolded protein response and coordinated increases in protein chaperones and activities that direct proteolysis, such as the 26S proteasome. Using RNA-seq analyses combined with chemical inhibitors or mutants that induce proteotoxic stress by impairing 26S proteasome capacity, we defined the transcriptional network that responds to this stress in Arabidopsis thaliana. This network includes genes encoding core and assembly factors needed to build the complete 26S particle, alternative proteasome capping factors, enzymes involved in protein ubiquitylation/deubiquitylation and cellular detoxification, protein chaperones, autophagy components, and various transcriptional regulators. Many loci in this proteasome-stress regulon contain a consensus cis-element upstream of the transcription start site, which was previously identified as a binding site for the NAM/ATAF1/CUC2 78 (NAC78) transcription factor. Double mutants disrupting NAC78 and its closest relative NAC53 are compromised in the activation of this regulon and notably are strongly hypersensitive to the proteasome inhibitors MG132 and bortezomib. Given that NAC53 and NAC78 homo-and heterodimerize, we propose that they work as a pair in activating the expression of numerous factors that help plants survive proteotoxic stress and thus play a central regulatory role in maintaining protein homeostasis.

Cloning, Characterization, and Expression Analysis of Eight Stress‐Related NAC Genes in Tartary Buckwheat

“…FtNAC6 and FtNAC7 were grouped with Arabidopsis ATAF1 and ATAF2 into the ATAF subgroup, which was involved in a diverse array of stress-related signaling processes (Christianson et al, 2010). Additionally, FtNAC9 together with ANAC053 and ANAC078 presented in the NAC2 subgroup, in which ANAC053 and ANAC078 were regulated by a reactive oxygen species metabolic process in Arabidopsis (Gladman et al, 2016). The above data may provide guidance for the functional identification of the eight FtNAC TFs.…”

“…ANAC053, ANAC055, ANAC072, and ANAC078 Lu et al, 2007;Christianson et al, 2010;Nakashima et al, 2012;Nuruzzaman et al, 2013;Gladman et al, 2016). NAC genes that belong to the same subgroup normally function similarly.…”

“…The FtNAC2 to FtNAC9 gene sequencing was consistent with the transcriptome and genome analysis. Additionally, FtNAC9 together with ANAC053 and ANAC078 presented in the NAC2 subgroup, in which ANAC053 and ANAC078 were regulated by a reactive oxygen species metabolic process in Arabidopsis (Gladman et al, 2016). As the result, only one copy was found for each FtNAC gene.…”

Differential submergence tolerance between juvenile and adult Arabidopsis plants involves the ANAC017 transcription factor

“…ANAC053 (At3g10500) and 78 (At5g04410), which formed a separate clade from ANAC013, 16 and 17 (Fig. 8a), have been recently reported to regulate the response to proteotoxic stress (Gladman et al , 2016). Limited to the members of the latter clade, interrogation of public gene expression datasets did not show significant differences at the transcriptional level between leaf samples from young or developed plants at the pre-flowering stage (Fig.…”

Mass Spectrometric Analyses Reveal a Central Role for Ubiquitylation in Remodeling the Arabidopsis Proteome during Photomorphogenesis

“…In this study, we analyzed 7-day-old etiolated seedlings either kept in the dark, irradiated with red light for 1 h, and/or exposed to 50 μM MG132 for 4 h before harvesting, which we found to be effective in inhibiting proteasomes (Kim et al, 2013; Gladman et al, 2016). A 2-h LC-MS/MS run typically detected ~3000–5000 PSMs that could be assigned to ~750 proteins on average.…”