Regulators of the ER Stress Response are Potential Repressors of Triterpene Saponin Biosynthesis in Medicago Truncatula

RIBEIRO, BIANCA; ERFFELINCK, MARIE-LAURE; PERASSOLO, MARÍA; VANDEN BOSSCHE, ROBIN; GOOSSENS, ALAIN

Viena

Conferencia; Plant Biotic Stresses & Resistance Mechanisms III; 2018

Triterpene saponins (TS) are specialized metabolites that share a biogenic origin with sterols and have a widespread distribution in the plant kingdom. Makibishi1 (MKB1) is an ERAD-like E3 ubiquitin ligase that regulates triterpene saponin (TS) biosynthesis in Medicago truncatula by targeting HMGR, the rate limiting enzyme for the production of TS precursors, for degradation. Silencing of MKB1 in M. truncatula hairy roots resulted in a severe phenotype with an enlarged ER and the upregulation of ER-stress marker genes. This suggests that MKB1 silenced lines are undergoing ER-stress and revealed a potential linkbetween ER-stress and the regulation of TS biosynthesis. To further investigate this, we carried out functional analysis of two bZIP transcription factors (TFs) that are known to be involved in ER stress by trans-activation and stress response assays. We obtained evidence supporting that both bZIP TFs mayrepress TS biosynthetic genes by counteracting the known positive regulators of TS biosynthesis, namely the Triterpene Saponin biosynthesis Activating Regulator (TSAR) TFs. Our findings forward a novel mechanism for interplay between ER stress and specialized metabolism in plants.