The Heat Shock Protein 40-Type Chaperone MASH Supports the Endoplasmic Reticulum-Associated Degradation E3 Ubiquitin Ligase MAKIBISHI1 in Medicago truncatula

Abstract

Jasmonates (JA) are oxylipin-derived phytohormones that trigger the production of specialized metabolites that often serve in defense against biotic stresses. In Medicago truncatula, a JA-induced endoplasmic reticulum-associated degradation (ERAD)-type machinery manages the production of bioactive triterpenes and thereby secures correct plant metabolism, growth, and development. This machinery involves the conserved RING membrane-anchor (RMA)-type E3 ubiquitin ligase MAKIBISHI1 (MKB1). Here, we discovered two additional members of this protein control apparatus via a yeast-based protein–protein interaction screen and characterized their function. First, a cognate E2 ubiquitin-conjugating enzyme was identified that interacts with MKB1 to deliver activated ubiquitin and to mediate its ubiquitination activity. Second, we identified a heat shock protein 40 (HSP40) that interacts with MKB1 to support its activity and was therefore designated MKB1-supporting HSP40 (MASH). MASH expression was found to be co-regulated with that of MKB1. The presence of MASH is critical for MKB1 and ERAD functioning because the dramatic morphological, transcriptional, and metabolic phenotype of MKB1 knock-down M. truncatula hairy roots was phenocopied by silencing of MASH. Interaction was also observed between the Arabidopsis thaliana (Arabidopsis) homologs of MASH and MKB1, suggesting that MASH represents an essential and plant-specific component of this vital and conserved eukaryotic protein quality control machinery.

Interference between ER stress-related bZIP-type and jasmonate-inducible bHLH-type transcription factors in the regulation of triterpene saponin biosynthesis in Medicago truncatula

“…MKB1 forms part of the ER-associated degradation (ERAD) machinery, which monitors the correct folding of membrane and secretory proteins whose biogenesis takes place in the ER. Recently, we also identified a heat shock protein 40 that interacts with MKB1 to support its activity (Erffelinck et al, 2021).When plants are evoked with environmental stresses, a programed defense response is launched, in which the ERAD, the unfolded protein response (UPR) and other ER stress responses play an important role (Malhotra and Kaufman, 2007;Liu and Howell, 2010b).…”

Bisphenol S Impairs Behaviors through Disturbing Endoplasmic Reticulum Function and Reducing Lipid Levels in the Brain of Zebrafish

“…35,66 The RNAseq and q-PCR data obtained at 48 hpf showed that the transcription of genes, including hsp70, hsp40, and hsp90, which are markers of ERAD, was increased by BPS treatment, indicating that the ability of the ER to degrade unfolded proteins was impaired. 67,68 The increases in the mRNA levels of genes encoding ER chaperones, including BiP, NEF, and GRP94, also indicated that the number of unfolded proteins was increased after 100 μg/L BPS exposure. These stressors disrupted protein processing in the ER, as indicated by the KEGG pathway analysis.…”

“…Considering that all ACS family-related genes are localized either exclusively or partially to the ER and hsd17b12a regulates LCFA elongation in the ER, the initial mechanism by which BPS inhibits LCFA elongation may be that BPS disturbs ER function and structure. The pathology of various neurodegenerative diseases involves the aggregation of misfolded proteins in the brain and aggregated unfolded and misfolded proteins induce ER stress by activating the PERK pathway and downstream signaling pathways. , The RNA-seq and q-PCR data obtained at 48 hpf showed that the transcription of genes, including hsp70 , hsp40 , and hsp90 , which are markers of ERAD, was increased by BPS treatment, indicating that the ability of the ER to degrade unfolded proteins was impaired. , The increases in the mRNA levels of genes encoding ER chaperones, including BiP, NEF, and GRP94, also indicated that the number of unfolded proteins was increased after 100 μg/L BPS exposure. These stressors disrupted protein processing in the ER, as indicated by the KEGG pathway analysis.…”

The saponin bomb: a nucleolar‐localized β‐glucosidase hydrolyzes triterpene saponins in Medicago truncatula

“…In M. truncatula , the JA‐responsive basic helix–loop–helix (bHLH) transcription factors (TFs) TRITERPENE SAPONIN ACTIVATION REGULATOR1 (TSAR1) 1 and TSAR2 were shown to directly trigger the concerted JA‐mediated transcriptional activation of the nonhemolytic and hemolytic TS biosynthesis genes, respectively (Mertens et al ., 2016). The JA signaling cascade also involves posttranslational mechanisms of TS biosynthesis, involving a subset of the endoplasmic reticulum (ER)‐associated degradation (ERAD) machinery, more specifically composed of the E3 ubiquitin ligase MAKIBISHI 1 and an interacting chaperone (Pollier et al ., 2013; Erffelinck et al ., 2021). This ERAD machinery controls TS biosynthesis in M. truncatula by controlling the levels of the enzyme 3‐HYDROXY‐3‐METHYLGLUTARYL‐COA REDUCTASE, which is a rate‐limiting enzyme for the biosynthesis of the triterpene precursor isopentenyl pyrophosphate (Pollier et al ., 2013).…”