Mutation in the Arabidopsis regulatory-associated protein TOR 1B (RAPTOR1B) leads to decreased jasmonates levels in leaf tissue

Mohamed A Salem,Patrick Giavalisco

doi:10.1080/15592324.2019.1649567

Abstract

ABSTRACTThe Target of Rapamycin (TOR) complex (TORC) regulates plant growth and development by modulation of metabolism in response to environmental cues. TORC contains in its core the TOR kinase and two interacting partners, namely; regulatory-associated partner of TOR (RAPTOR) and lethal with sec thirteen protein 8 (LST8). RAPTOR is described to act as a scaffold protein which recruits substrates for phosphorylation to the TOR kinase.In the current manuscript we show that mutation of Arabidopsis RAPTOR1B leads to significantly decreased levels of free jasmonic acid (JA), jasmonoyl-(L)-isoleucine (JA-Ile) as well as its biosynthetic precursor 12-oxo-phytodienoic acid (OPDA). Although raptor1b leaves showed decreased basic JA level compared to WT, the mutant responded substantially to wounding stress by producing the same amount of JA as WT. Furthermore, we could show that the chemical inhibition of TOR by AZD-8055 led to an opposite response. AZD-treated WT and raptor1b leaves accumulated high JA levels. These results strongly imply that the TOR signaling pathway is responding differentially to the inhibition of the TOR kinase as compared to the inhibition of the scaffold protein RAPTOR.

Highlights

The Target of Rapamycin (TOR) complex (TORC) regulates plant growth and development by modulation of metabolism in response to environmental cues
The results showed that the endogenous jasmonate concentrations of oxo-phytodienoic acid (OPDA), jasmonic acid (JA)-Ile and free JA were significantly decreased in raptor1b leaves (Figure 1)
WT showed a significant increase in endogenous JA (B), JA-Ile (C) and OPDA (D) levels after 30 min and 48 h of AZD treatment of Arabidopsis WT growing in seedling cultures.17-days-old seedlings of WT and raptor1b seedlings grown on 0.5x MS agar were harvested after 3 days of treatment with 1 μM AZD in DMSO

Summary

Introduction

The Target of Rapamycin (TOR) complex (TORC) regulates plant growth and development by modulation of metabolism in response to environmental cues. JA and its precursor OPDA are known to regulate different aspects of plant growth and they have been shown to inhibit seed germination.[30,33–35] We recently reported increased levels of JA and OPDA and delayed germination in raptor1b mutated seeds.[9] To further investigate the cross talk between RAPTOR1B and JA in vegetative tissue, we measured jasmonate levels in developmentally matched (10-rosette leaf stage)[36] WT and raptor1b leaves.

Results

Conclusion