Oxylipins From Different Pathways Trigger Mitochondrial Stress Signaling Through Respiratory Complex III

Abstract

Plant oxylipins are signaling molecules produced from fatty acids by oxidative pathways, mainly initiated by 9- and 13-lipoxygenases (9-LOX and 13-LOX), alpha-dioxygenases or non-enzymatic oxidation. Oxylipins from the 9-LOX pathway induce oxidative stress and control root development and plant defense. These activities have been associated with mitochondrial processes, but precise cellular targets and pathways remain unknown. In order to study oxylipin signaling, we previously generated a collection of Arabidopsis thaliana mutants that were insensitive to the 9-LOX products 9(S)-hydroxy-10,12, 15-octadecatrienoic acid (9-HOT) and its ketone derivative 9-KOT (noxy mutants). Here, we describe noxy1, noxy3, noxy5, noxy23, and noxy54 mutants, all affected in nucleus-encoded mitochondrial proteins, and use them to study the role of mitochondria in oxylipin signaling. Functional and phenotypic analyses showed that noxy plants displayed mitochondrial aggregation, reduced respiration rates and resistance to the complex III inhibitor Antimycin A (AA), thus indicating a close similarity of the oxylipin signaling and mitochondrial stress. Application of 9-HOT and 9-KOT protected plants against subsequent mitochondrial stress, whereas they boosted root growth reduction when applied in combination with complex III inhibitors but did not with inhibitors of other respiratory complexes. A similar effect was caused by linear-chain oxylipins from 13-LOX or non-enzymatic pathways having α,β-unsaturated hydroxyl or keto groups in their structure. Studies to investigate 9-HOT and 9-KOT activity indicated that they do not reduce respiration rates, but their action is primarily associated with enhanced ROS responses. This was supported by the results showing that 9-HOT or 9-KOT combined with AA amplified the expression of oxylipin- and ROS-responding genes but not of the AA marker AOX1a, thus implying the activation of a specific mitochondria retrograde signaling pathway. Our results implicate mitochondrial complex III as a hub in the signaling activity of multiple oxylipin pathways and point at downstream ROS responses as components of oxylipin function.

Mutant noxy8 exposes functional specificities between the chloroplast chaperones CLPC1 and CLPC2 in the response to organelle stress and plant defence

“…We previously identified noxy mutations in nucleus‐encoded mitochondrial proteins that alter mitochondrial behaviour (Izquierdo et al, 2021; Vellosillo et al, 2013). Those mutants had lower respiration rates and resistance to the respiration inhibitor AA (Izquierdo et al, 2021).…”

“…We previously identified noxy mutations in nucleus‐encoded mitochondrial proteins that alter mitochondrial behaviour (Izquierdo et al, 2021; Vellosillo et al, 2013). Those mutants had lower respiration rates and resistance to the respiration inhibitor AA (Izquierdo et al, 2021). These parameters were examined in isolated mitochondria of clpc mutants, demonstrating that the capacity of both cytochrome and alternative respiration pathways were unaffected in clpc2 and clpc1 plants (Figure 4a).…”

“…Previous studies with the products of 9-LOX, 9-HOT and 9-KOT, demonstrated their participation in the activation of plant defence and retrograde mitochondria signalling (Izquierdo et al, 2021;Vicente et al, 2012). Here, we focused on noxy8, from a series of Arabidopsis 9-HOT insensitive mutants (noxy), to further investigate oxylipin signalling.…”

“…The response to 9‐HOT and 9‐KOT is impaired in noxy ( nonresponding to oxylipins ) mutants with alterations in mitochondrial proteins. Highlighting the relevance of mitochondria in oxylipin signalling, mutants noxy2, noxy15/drp3a‐1, noxy38/fmt‐1, noxy1, noxy3/lon1‐3, noxy5, noxy23 and noxy54/ahg2‐3 accumulate abnormal mitochondrial aggregates, and display reduced respiration rates and resistance to Antimycin A (AA), an inhibitor of mitochondrial electron transfer at complex III (Izquierdo et al, 2021; Vellosillo et al, 2013).…”

Osmotic stress in roots drives lipoxygenase-dependent plastid remodeling through singlet oxygen production

“…Cell death by singlet oxygen can occur through direct inactivation of the membrane, protein and nucleic acid components of the cellular machinery (Koh et al, 2021; Koh and Fluhr, 2016). Furthermore, singlet oxygen can modify the oxylipins produced and change their potency (Izquierdo et al, 2021). Importantly, lipoxygenase activity does not have to be induced by the stress as their basal activity is chiefly limited by the availability of fatty acid substrate (Chen et al, 2021).…”