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

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,ß-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.

Diverse population of a new bipartite begomovirus infecting tomato crops in Uruguay.

Several isolates of a novel begomovirus were characterized from tomato samples collected in northern Uruguay exhibiting disease symptoms associated with Bemisia tabaci infestations. Analysis of full-length sequences of DNA-A and DNA-B components revealed the presence of a new begomovirus with the typical genome organization of a New World begomovirus, for which the name tomato rugose yellow leaf curl virus (ToRYLCV) is proposed. A high degree of nucleotide sequence diversity was found for both components, suggesting the presence of a diverse virus population. Recombination analysis suggested relationships of ToRYLCV to begomoviruses reported from the New World. Although common regions from DNA-As and DNA-Bs were surprisingly divergent for a cognate pair, a DNA-A and DNA-B pair cloned from one sample were infectious in Nicotiana benthamiana and tomato and reproduced symptoms observed in field-infected tomato plants, suggesting that ToRYLCV is the causal agent of the disease observed. This is the first report of a begomovirus infecting tomato crops in Uruguay and of the presence of begomovirus in this country.