Insights into a key sulfite scavenger enzyme sulfite oxidase (SOX) gene in plants

Peroxisomal H2O2-generating sulfite oxidase (SOX) from pepper fruits is negatively modulated by NO and H2S

Nitric oxide and hydrogen sulfide are signal molecules that can exert regulatory functions in diverse plant processes including fruit ripening. Sulfite oxidase (SOX) is a peroxisomal enzyme that catalyzes the oxidation of sulfite (SO32-) to sulfate (SO42-) with the concomitant generation of H2O2. SOX requires the molybdenum cofactor (Moco) and it has been proposed that SOX functions as a mechanism of protection against sulfite toxicity. Based on the analysis of the pepper genome and fruit transcriptome (RNA-seq), a single gene encoding for a SOX, was identified in chromosome 2. The CaSOX gene expression analysis during fruit ripening, from green immature (G) to red ripe (R) indicates that its expression increased. In-gel analysis using non-denaturing PAGE of a 50-75% (NH4)2SO4 protein fraction allowed the detection of its SOX activity in green pepper fruits. In vitro assay of the SOX from pepper fruits showed that the SOX activity is differently regulated by NO and H2S. Mass spectrometric analysis of the nitrated recombinant pepper SOX enables us to corroborate that this enzyme undergoes inhibition by nitration in Tyr10. Protein modeling analysis also reveals that Cys70 and Cys163 are susceptible targets for S-nitrosation and persulfidation. These findings suggest that NO and H2S could function upstream of the peroxisomal H2O2-generating SOX, highlighting the intricate network of signaling molecules within this subcellular compartment.

A cotton mitochondrial alternative electron transporter, GhD2HGDH, induces early flowering by modulating GA and photoperiodic pathways

D-2-hydroxyglutarate dehydrogenase (D2HGDH) is a mitochondrial enzyme containing flavin adenine dinucleotide FAD, existing as a dimer, and it facilitates the specific oxidation of D-2HG to 2-oxoglutarate (2-OG), which is a key intermediate in the tricarboxylic acid (TCA) cycle. A Genome-wide expression analysis (GWEA) has indicated an association between GhD2HGDH and flowering time. To further explore the role of GhD2HGDH, we performed a comprehensive investigation encompassing phenotyping, physiology, metabolomics, and transcriptomics in Arabidopsis thaliana plants overexpressing GhD2HGDH. Transcriptomic and qRT-PCR data exhibited heightened expression of GhD2HGDH in upland cotton flowers. Additionally, early-maturing cotton exhibited higher expression of GhD2HGDH across all tissues than delayed-maturing cotton. Subcellular localization confirmed its presence in the mitochondria. Overexpression of GhD2HGDH in Arabidopsis resulted in early flowering. Using virus-induced gene silencing (VIGS), we investigated the impact of GhD2HGDH on flowering in both early- and delayed-maturing cotton plants. Manipulation of GhD2HGDH expression levels led to changes in photosynthetic pigment and gas exchange attributes. GhD2HGDH responded to gibberellin (GA3) hormone treatment, influencing the expression of GA biosynthesis genes and repressing DELLA genes. Protein interaction studies, including yeast two-hybrid, luciferase complementation (LUC), and GST pull-down assays, confirmed the interaction between GhD2HGDH and GhSOX (Sulfite oxidase). The metabolomics analysis demonstrated GhD2HGDH's modulation of the TCA cycle through alterations in various metabolite levels. Transcriptome data revealed that GhD2HGDH overexpression triggers early flowering by modulating the GA3 and photoperiodic pathways of the flowering core factor genes. Taken together, GhD2HGDH positively regulates the network of genes associated with early flowering pathways.

Alleviating excess boron stress in tomato calli by applying benzoic acid to various biochemical strategies

Benzoic acid (BA) represents vital roles in plant activity and response to diverse unfavorable conditions. However, its participation in mitigating excess boron (EB) stress in plants is elusive. Herein, we have examined the impacts of BA (1 μM) in controlling boron (B) uptake in tomato (Solanum lycopersicum L.) calli exposed to various EB levels (0, 1, 2, and 3 mM). The free, semi-bound, and bound B forms were stimulated by EB, while these forms were reduced in B-stressed calli by BA supplementation (40.37%, 36.08%, and 66.91%, respectively, less than 3 mM B-stressed calli alone). EB caused a reduction in the uptake of potassium (K⁺), calcium (Ca²⁺), magnesium (Mg²⁺), and nitrite (NO₂^-) while increasing the concentration of phosphorus (P), nitrate (NO₃^-), sulfur (S), and sulfate (SO₄^2-) in B-stressed calli. BA application induced the uptake of K⁺, Ca²⁺, Mg²⁺, NO₃^-, S, and SO₄^2-; however, it reduced P and NO₂^- concentrations in B-stressed calli. EB reduced nitrate reductase activity (NR), while BA application did not alleviate this reduction. EB treatments significantly, in most cases, increased sulfite oxidase (SO) activity. Supplementation of BA along with EB further enhanced SO activity. Cell wall components (cellulose, hemicellulose, and pectin) were decreased under EB treatments but considerably increased in B-stressed calli by BA application. Fourier Transform Infrared Spectrometer (FT-IR) output showed that EB treatments with/without BA led to alterations in cell wall functional groups of calli. Our findings indicated that BA application enabled tomato callus to counteract the harmful effect of EB, leading to improved callus growth.

Proteomic and ecophysiological responses of soybean (Glycine max L.) root nodules to Pb and hg stress

BACKGROUND

Lead (Pb) and mercury (Hg) are persistent hazardous metals in industrially polluted soils which can be toxic in low quantities. Metal toxicity can cause changes at cellular and molecular level which should be studied for better understanding of tolerance mechanism in plants. Soybean (Glycine max L.) is an important oilseed crop of the world including India. Indian soils growing soybean are often contaminated by Pb and Hg. The aim of this study was to explore how soybean root nodule responds to Pb and Hg through proteomic and ecophysiological alterations in order to enhance tolerance to metal stress.

RESULTS

Soybean plants were exposed to Pb (30 ppm PbCl2) and Hg (0.5 ppm HgCl2) to study histological, histochemical, biochemical and molecular response of N2-fixing symbiotic nodules. Both Pb and Hg treatment increased the level of oxidative stress in leaves and nodules. Chlorosis in leaves and morphological/anatomical changes in nodules were observed. Activities of ascorbate peroxidase, glutathione reductase and catalase were also modulated. Significant changes were observed in abundance of 76 proteins by Pb and Hg. Pb and Hg influenced abundance of 33 proteins (17 up and 16 down) and 43 proteins (33 up and 10 down), respectively. MS/MS ion search identified 55 proteins which were functionally associated with numerous cellular functions. Six crucial proteins namely catalase (CAT), allene oxide synthase (AOS), glutathione S-transferase (GST), calcineurin B like (CBL), calmodulin like (CML) and rapid alkalinisation factor (RAF) were selected for transcript abundance estimation. The qRT-PCR based real time expression exhibited a positive correlation with proteomics expression except for GST and RAF.

CONCLUSION

Soybean root nodule responds to metal stress by increased abundance of defence, development and repair related proteins. An efficient proteomic modulation might lead to metal-induced stress tolerance in N2-fixing nodules. Although concentrations of Pb and Hg used in the study cannot be considered equimolar, yet Hg seems to induce more changes in nodule proteomic profile, and higher damage to both bacteroides and root anatomy.

Overexpression of the Maize Sulfite Oxidase Increases Sulfate and GSH Levels and Enhances Drought Tolerance in Transgenic Tobacco

Sulfite oxidase (SO) plays a pivotal role in sulfite metabolism. In our previous study, sulfite-oxidizing function of the SO from Zea mays (ZmSO) was characterized. To date, the knowledge of ZmSO's involvement in abiotic stress response is scarce. In this study, we aimed to investigate the role of ZmSO in drought stress. The transcript levels of ZmSO were relatively high in leaves and immature embryos of maize plants, and were up-regulated markedly by PEG-induced water stress. Overexpression of ZmSO improved drought tolerance in tobacco. ZmSO-overexpressing transgenic plants showed higher sulfate and glutathione (GSH) levels but lower hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) contents under drought stress, indicating that ZmSO confers drought tolerance by enhancing GSH-dependent antioxidant system that scavenged ROS and reduced membrane injury. In addition, the transgenic plants exhibited more increased stomatal response than the wild-type (WT) to water deficit. Interestingly, application of exogenous GSH effectively alleviated growth inhibition in both WT and transgenic plants under drought conditions. qPCR analysis revealed that the expression of several sulfur metabolism-related genes was significantly elevated in the ZmSO-overexpressing lines. Taken together, these results imply that ZmSO confers enhanced drought tolerance in transgenic tobacco plants possibly through affecting stomatal regulation, GSH-dependent antioxidant system, and sulfur metabolism-related gene expression. ZmSO could be exploited for developing drought-tolerant maize varieties in molecular breeding.