Lipoxygenases and plant cell metabolism regulation

Grafting enhances drought tolerance by regulating and mobilizing proteome, transcriptome and molecular physiology in okra genotypes

Drought stress poses a serious concern to the growth, development, and quality of the okra crop due to factors including decreased yield, inadequate development of dietary fibre, increased mite infestation, and decreased seed viability. Grafting is one of the strategies that have been developed to increase the drought stress tolerance of crops. We conducted proteomics, transcriptomics and integrated it with molecular physiology to assess the response of sensitive okra genotypes; NS7772 (G1), Green gold (G2) and OH3312 (G3) (scion) grafted to NS7774 (rootstock). In our studies we observed that sensitive okra genotypes grafted to tolerant genotypes mitigated the deleterious effects of drought stress through an increase in physiochemical parameters, and lowered reactive oxygen species. A comparative proteomic analysis showed a stress responsive proteins related to Photosynthesis, energy and metabolism, defence response, protein and nucleic acid biosynthesis. A proteomic investigation demonstrated that scions grafted onto okra rootstocks increased more photosynthesis-related proteins during drought stress, indicating an increase in photosynthetic activity when plants were subjected to drought stress. Furthermore, transcriptome of RD2, PP2C, HAT22, WRKY and DREB increased significantly, specifically for grafted NS7772 genotype. Furthermore, our study also indicated that grafting improved the yield components such as number of pods and seeds per plant, maximum fruit diameter, and maximum plant height in all genotypes which directly contributed towards their high resistance towards drought stress.

The lipoxygenase OsLOX10 affects seed longevity and resistance to saline-alkaline stress during rice seedlings

Prolonged storage of rice seeds can lead to a decrease in seed vigor and seedling quality. The Lipoxygenase (LOX) gene family is widely distributed in plants, and LOX activity is closely related to seed viability and stress tolerance. In this study, the lipoxygenase OsLOX10 gene from the 9-lipoxygenase metabolic pathway was cloned from rice, and its roles in determining seed longevity and tolerance to saline-alkaline stress caused by Na₂CO₃ in rice seedlings were mainly investigated. CRISPR/Cas9 knockout of OsLOX10 increased seed longevity compared with the wild-type and OsLOX10 overexpression lines in response to artificial aging. The expression levels of other 9-lipoxygenase metabolic pathway related genes, such as LOX1, LOX2 and LOX3, were increased in the LOX10 overexpression lines. Quantitative real-time PCR and histochemical staining analysis showed that the expression of LOX10 was highest in seed hulls, anthers and the early germinating seeds. KI-I₂ staining of starch showed that LOX10 could catalyze the degradation of linoleic acid. Furthermore, we found that the transgenic lines overexpressing LOX10 showed better tolerance to saline-alkaline stress than the wild-type and knockout mutant lines. Overall, our study demonstrated that the knockout LOX10 mutant increased seed longevity, whereas overexpression of LOX10 enhanced tolerance to saline-alkaline stress in rice seedlings.

Specific Roles of Lipoxygenases in Development and Responses to Stress in Plants

Lipoxygenases (LOXs), naturally occurring enzymes, are widely distributed in plants and animals. LOXs can be non-sulfur iron, non-heme iron, or manganese-containing dioxygenase redox enzymes. LOXs catalyze the oxidation of polyunsaturated fatty acids into fatty acid hydroperoxides. Linolenic acid, a precursor in the jasmonic acid (JA) biosynthesis, is converted to 12-oxo-phytodienoic acid through oxygenation with LOX, allene oxide synthase, and allene oxide cyclase. Moreover, JA participates in seed germination, fruit ripening, senescence, and many other physio-biochemical processes. LOXs also play crucial roles in defense responses against biotic stress, i.e., insects, pests, pathogenic attacks, and abiotic stress, such as wounding, UV-rays, extreme temperature, oxidative stress, and drought.

The Molecular and Functional Characterization of the Durum Wheat Lipoxygenase TdLOX2 Suggests Its Role in Hyperosmotic Stress Response

In plants, lipoxygenases (LOXs) are involved in various processes, such as growth, development, and response to stress cues. In the present study, the expression pattern of six durum wheat LOX-encoding genes (TdLpx-B1.1, TdLpx-B1.2, TdLpx-A2, TdLpx-B2, TdLpx-A3 and TdLpx-B3) under hyperosmotic stress was investigated. With osmotic (0.42 M mannitol) and salt (0.21 M NaCl) stress imposed at the early stages of seedling growth, a strong induction of the TdLpx-A2 gene expression in the shoots paralleled an equally strong increase in the LOX activity. Enhanced levels of malondialdehyde (MDA) and increased rates of superoxide anion generation were also observed as a result of the stress imposition. Sequence analysis of the TdLOX2 encoded by the TdLpx-A2 gene revealed that it belonged to the type-1 9-LOX group. When overexpressed in E. coli, TdLOX2 exhibited normal enzyme activity, high sensitivity to specific LOX inhibitors, with 76% and 99% inhibition by salicylhydroxamic and propyl gallate, respectively, and a preference for linoleic acid as substrate, which was converted exclusively to its corresponding 13-hydroperoxide. This unexpected positional specificity could be related to the unusual TV/K motif that in TdLOX2 replaces the canonical TV/R motif of 9-LOXs. Treatment of seedlings with propyl gallate strongly suppressed the increase in LOX activity induced by the hyperosmotic stress; the MDA accumulation was also reduced but less markedly, whereas the rate of superoxide anion generation was even more increased. Overall, our findings suggest that the up-regulation of the TdLpx-A2 gene is a component of the durum wheat response to hyperosmotic stress and that TdLOX2 may act by counteracting the excessive generation of harmful reactive oxygen species responsible for the oxidative damages that occur in plants under stress.