Lipoxygenase 2 functions in exogenous nitric oxide-induced stomatal closure in Arabidopsis thaliana

Soybean (Glycine max L.) Lipoxygenase 1 (LOX 1) Is Modulated by Nitric Oxide and Hydrogen Sulfide: An In Vitro Approach

Hydrogen sulfide (H₂S) and nitric oxide (NO) are two relevant signal molecules that can affect protein function throughout post-translational modifications (PTMs) such as persulfidation, S-nitrosation, metal-nitrosylation, and nitration. Lipoxygenases (LOXs) are a group of non-heme iron enzymes involved in a wide range of plant physiological functions including seed germination, plant growth and development, and fruit ripening and senescence. Likewise, LOXs are also involved in the mechanisms of response to diverse environmental stresses. Using purified soybean (Glycine max L.) lipoxygenase type 1 (LOX 1) and nitrosocysteine (CysNO) and sodium hydrosulfide (NaHS) as NO and H₂S donors, respectively, the present study reveals that both compounds negatively affect LOX activity, suggesting that S-nitrosation and persulfidation are involved. Mass spectrometric analysis of nitrated soybean LOX 1 using a peroxynitrite (ONOO^-) donor enabled us to identify that, among the thirty-five tyrosine residues present in this enzyme, only Y214 was exclusively nitrated by ONOO^-. The nitration of Y214 seems to affect its interaction with W500, a residue involved in the substrate binding site. The analysis of the structure 3PZW demonstrates the existence of several tunnels that directly communicate the surface of the protein with different internal cysteines, thus making feasible their potential persulfidation, especially C429 and C127. On the other hand, the CysNO molecule, which is hydrophilic and bulkier than H₂S, can somehow be accommodated throughout the tunnel until it reaches C127, thus facilitating its nitrosation. Overall, a large number of potential persulfidation targets and the ease by which H₂S can reach them through the diffuse tunneling network could be behind their efficient inhibition.

Protuberances are organized distinct regions of long-term callus: histological and transcriptomic analyses in kiwifruit

KEY MESSAGE

Macroscopic, ultrastructural, and molecular features-like a ball shape, the presence of starch granules, and the up-regulation of genes involved in carbohydrate metabolism and secondary metabolite biosynthesis-distinguish PT regions within a callus. The modification of the mass of pluripotent cells into de novo shoot bud regeneration is highly relevant to developmental biology and for agriculture and biotechnology. This study deals with protuberances (PT), structures that appear during the organogenic long-term culturing of callus (OC) in kiwifruit. These ball-shaped regions of callus might be considered the first morphological sign of the subsequent shoot bud development. Sections of PT show the regular arrangement of some cells, especially on the surface, in contrast to the regions of OC beyond the PT. The cells of OC possess chloroplasts; however, starch granules were observed only in PTs' plastids. Transcriptomic data revealed unique gene expression for each kind of sample: OC, PT, and PT with visible shoot buds (PT-SH). Higher expression of the gene involved in lipid (glycerol-3-phosphate acyltransferase 5 [GPAT5]), carbohydrate (granule-bound starch synthase 1 [GBSS1]), and secondary metabolite (beta-glucosidase 45 [BGL45]) pathways were detected in PT and could be proposed as the markers of these structures. The up-regulation of the regulatory associated protein of TOR (RAPTOR1) was found in PT-SH. The highest expression of the actinidain gene in leaves from two-year-old regenerated plants suggests that the synthesis of this protein takes place in fully developed organs. The findings indicate that PT and PT-SH are specific structures within OC but have more features in common with callus tissue than with organs.

CmLOX10 positively regulates drought tolerance through jasmonic acid -mediated stomatal closure in oriental melon (Cucumis melo var. makuwa Makino)

Drought stress severely impairs plant growth and production. Lipoxygenase (LOX), a master regulator for lipid peroxidation, is critical for direct or indirect response to abiotic stresses. Here, we found that drought stress induced the transcription of CmLOX10 in leaves of oriental melon seedlings. Reverse genetic approaches and physiological analyses revealed that silencing CmLOX10 increased drought susceptibility and stomatal aperture in oriental melon seedlings, and that ectopic overexpression of CmLOX10 in Arabidopsis enhanced drought tolerance and decreased the stomatal aperture. Moreover, the transcription of jasmonic acid (JA)-related genes and JA accumulation were significantly induced in CmLOX10-overexpressed Arabidopsis, which were reversely suppressed in CmLOX10-silenced seedlings during the stage of drought stress. Foliar application of JA further verified that JA enhanced drought tolerance and induced stomatal closure in leaves of melon seedlings. In addition, the feedback regulation of CmLOX10 was induced by JA signaling, and the expression level of CmMYC2 was increased by JA and drought treatment. Yeast one-hybrid analysis showed that CmMYC2 directly bound to the promoter of CmLOX10. In summary, we identified the important roles of CmLOX10 in the regulation of drought tolerance in oriental melon seedlings through JA- mediated stomatal closure and JA signaling-mediated feedback through CmMYC2.

H2S induces NO in the regulation of AsA-GSH cycle in wheat seedlings by water stress

In current study, we investigated the relationship between hydrogen sulfide (H₂S) and nitric oxide (NO) in the regulation of ascorbate-glutathione (AsA-GSH) cycle in wheat seedlings by water stress. Findings showed that water stress significantly stimulated the production of H₂S and NO, the transcript levels and activities of enzymes in AsA-GSH cycle, as well as malondialdehyde (MDA) production and electrolyte leakage, but significantly decreased AsA/DHA and GSH/GSSG. Meanwhile, water stress significantly decreased plant height and dry biomass. Except MDA and electrolyte leakage, above changes induced by water stress were reversed by H₂S synthesis inhibitor aminooxyacetic acid (AOA) and NO synthesis inhibitor N^G-nitro-L-arginine methyl ester (L-NAME). However, AOA and L-NAME significantly enhanced MDA production and electrolyte leakage, which further decreased plant height and dry biomass of wheat seedlings under water stress. Application of exogenous H₂S donor sodium hydrosulfide (NaHS) to AOA-treated plants and application of exogenous NO donor sodium nitroprusside (SNP) to L-NAME-treated plants reversed above effects of AOA and L-NAME, respectively. Application of L-NAME plus water stress significantly decreased NO production induced by water stress. However, application of L-NAME plus water stress had no obvious influence on H₂S production induced by water stress, while application of AOA plus water stress significantly reduced the production of H₂S and NO induced by water stress. Current findings suggested that H₂S acted upstream of NO in the regulation of AsA-GSH cycle in wheat seedlings by water stress.

Comparative Transcriptome Analysis of Two Aegilops tauschii with Contrasting Drought Tolerance by RNA-Seq

As the diploid progenitor of common wheat, Aegilops tauschii is considered to be a valuable resistance source to various biotic and abiotic stresses. However, little has been reported concerning the molecular mechanism of drought tolerance in Ae. tauschii. In this work, the drought tolerance of 155 Ae. tauschii accessions was firstly screened on the basis of their coleoptile lengths under simulated drought stress. Subsequently, two accessions (XJ002 and XJ098) with contrasting coleoptile lengths were selected and intensively analyzed on rate of water loss (RWL) as well as physiological characters, confirming the difference in drought tolerance at the seedling stage. Further, RNA-seq was utilized for global transcriptome profiling of the two accessions seedling leaves under drought stress conditions. A total of 6969 differentially expressed genes (DEGs) associated with drought tolerance were identified, and their functional annotations demonstrated that the stress response was mediated by pathways involving alpha-linolenic acid metabolism, starch and sucrose metabolism, peroxisome, mitogen-activated protein kinase (MAPK) signaling, carbon fixation in photosynthetic organisms, and glycerophospholipid metabolism. In addition, DEGs with obvious differences between the two accessions were intensively analyzed, indicating that the expression level of DEGs was basically in alignment with the physiological changes of Ae. tauschii under drought stress. The results not only shed fundamental light on the regulatory process of drought tolerance in Ae. tauschii, but also provide a new gene resource for improving the drought tolerance of common wheat.

Update on roles of nitric oxide in regulating stomatal closure

Nitric oxide (NO) as an important secondary messager plays crucial roles in modulating stomatal movement, especially abscisic acid (ABA)-induced stomatal closure. Accumulating evidence indicates that NO positively and negatively regulates guard cell ABA signaling. NO is also implicated in stomatal closure mediated by hydrogen sulfide, small peptides, polyamines, and methyl jasmonate. In this review, we summarize recent advances on the roles and the underlying mechanisms of NO in regulating stomatal closure in plants.