Metabolite Regulatory Interactions Control Plant Respiratory Metabolism via Target of Rapamycin (TOR) Kinase Activation

Abstract

Respiration rate measurements provide an important readout of energy expenditure and mitochondrial activity in plant cells during the night. As plants inhabit a changing environment, regulatory mechanisms must ensure that respiratory metabolism rapidly and effectively adjusts to the metabolic and environmental conditions of the cell. Using a high-throughput approach, we have directly identified specific metabolites that exert transcriptional, translational, and posttranslational control over the nighttime O 2 consumption rate (R N) in mature leaves of Arabidopsis (Arabidopsis thaliana). Multi-hour R N measurements following leaf disc exposure to a wide array of primary carbon metabolites (carbohydrates, amino acids, and organic acids) identified phosphoenolpyruvate (PEP), Pro, and Ala as the most potent stimulators of plant leaf R N. Using metabolite combinations, we discovered metabolite-metabolite regulatory interactions controlling R N. Many amino acids, as well as Glc analogs, were found to potently inhibit the R N stimulation by Pro and Ala but not PEP. The inhibitory effects of amino acids on Pro-and Ala-stimulated R N were mitigated by inhibition of the Target of Rapamycin (TOR) kinase signaling pathway. Supporting the involvement of TOR, these inhibitory amino acids were also shown to be activators of TOR kinase. This work provides direct evidence that the TOR signaling pathway in plants responds to amino acid levels by eliciting regulatory effects on respiratory energy metabolism at night, uniting a hallmark mechanism of TOR regulation across eukaryotes.

BREAKTHROUGH REPORT - Large scale measurement of protein synthesis rates over the diurnal cycle reveal pathway specific regulation of translation

“…This effect paces starch usage, allowing plants to avoid carbon starvation at the end of the night (Sulpice et al 2014) and delayed growth the following day (Gibon, Bläsing, et al 2004). The high Spearman correlation of translation rate ranking between the day and the night, with overall lower rates at night agrees well with notion of general translational regulation promoting translation during the day and supressing it at night (OLeary et al 2020; Merchante et al 2017;Moore et al 2016). This is also reflected by the bulk of the proteins measured here (~60%) moving less than 30 ranks in translation order between the day and the night (Supplemental Table S2).…”

Shedding Light on the Dynamic Role of the “Target of Rapamycin” Kinase in the Fast-Growing C4 Species Setaria viridis, a Suitable Model for Biomass Crops

“…Pro and its regulators WRKY54 and WRKY70 (Li et al, 2013) were also elevated in this species. Recently, high abundances of Pro and other amino acids were implicated in inhibited leaf respiration under TORC control at nighttime (O'Leary et al, 2020). The A. thaliana lst8-1 mutant also displays higher Pro content, which is amplified after transference from short to long days, and fails to produce raffinose and galactinol that replace Pro during this adaptation to longer light periods (Moreau et al, 2012).…”

The mitochondrial pyruvate carrier (MPC) complex is one of three pyruvate-supplying pathways that sustain Arabidopsis respiratory metabolism

“…It is made available under a preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in this work introduces AlaAT as a major flux contributor to the canonical pyruvate supply pathways by efficiently bypassing pyruvate import from the cytosol to the mitochondrial matrix rather than just being considered a stress response pathway (Ricoult et al, 2006;Miyashita and Good, 2008;Diab and Limami, 2016). In this context it is notable that a positive correlation of respiratory rates in Arabidopsis leaves was more apparent for alanine than for pyruvate, sugars or other organic and amino acids (O'Leary et al, 2017) and alanine is a strong stimulator of respiratory rate in vivo in Arabidopsis (O'Leary et al, 2020).…”