Selective silencing of 2Cys and type-IIB Peroxiredoxins discloses their roles in cell redox state and stress signaling

Systematic analysis of Prx genes in the Brachypodium genus and their expression pattern under abiotic constraints

Peroxiredoxins (Prx) are ubiquitous peroxidases required for the removal of excess free radicals produced under stress conditions. Peroxiredoxin genes (Prx) in the Brachypodium genus were identified using bioinformatics tools and their expression profiles were determined under abiotic stress using RT-qPCR. The promoter regions of Prx genes contain several cis-acting elements related to stress response. In silico expression analysis showed that B. distachyon Prx genes (BdPrx) are tissue specific. RT-qPCR analysis revealed their differential expression when exposed to salt or PEG-induced dehydration stress. In addition, the upregulation of BdPrx genes was accompanied by accumulation of H2 O2 . Exogenous application of H2 O2 induced expression of almost all BdPrx genes. The identified molecular interaction network indicated that Prx proteins may contribute to abiotic stress tolerance by regulating key enzymes involved in lignin biosynthesis. Overall, our findings suggest the potential role of Prx genes in abiotic stress tolerance and lay the foundation for future functional analyses aiming to engineer genetically improved cereal lines.

Redox-mediated responses to high temperature in plants

As sessile organisms, plants are particularly affected by climate change and will face more frequent and extreme temperature variations in the future. Plants have developed a diverse range of mechanisms allowing them to perceive and respond to these environmental constraints, which requires sophisticated signalling mechanisms. Reactive oxygen species (ROS) are generated in plants exposed to various stress conditions including high temperatures and are presumed to be involved in stress response reactions. The diversity of ROS-generating pathways and the ability of ROS to propagate from cell to cell and to diffuse through cellular compartments and even across membranes between subcellular compartments put them at the centre of signalling pathways. In addition, their capacity to modify the cellular redox status and to modulate functions of target proteins, notably through cysteine oxidation, show their involvement in major stress response transduction pathways. ROS scavenging and thiol reductase systems also participate in the transmission of oxidation-dependent stress signals. In this review, we summarize current knowledge on the functions of ROS and oxidoreductase systems in integrating high temperature signals, towards the activation of stress responses and developmental acclimation mechanisms.

TaBAS1 encoding a typical 2-Cys peroxiredoxin enhances salt tolerance in wheat

Efficient antioxidant enzymatic system contributes to salt tolerance of plants via avoiding ROS over-accumulation. Peroxiredoxins are crucial components of the reactive oxygen species (ROS) scavenging machinery in plant cells, but whether they offer salt tolerance with potential for germplasm improvement has not been well addressed in wheat. In this work, we confirmed the role of a wheat 2-Cys peroxiredoxin gene TaBAS1 that was identified through the proteomic analysis. TaBAS1 overexpression enhanced the salt tolerance of wheat at both germination and seedling stages. TaBAS1 overexpression enhanced the tolerance to oxidative stress, promoted the activities of ROS scavenging enzymes, and reduced ROS accumulation under salt stress. TaBAS1 overexpression promoted the activity of ROS production associated NADPH oxidase, and the inhibition of NADPH oxidase activity abolished the role of TaBAS1 in salt and oxidative tolerance. Moreover, the inhibition of NADPH-thioredoxin reductase C activity erased the performance of TaBAS1 in the tolerance to salt and oxidative stress. The ectopic expression of TaBAS1 in Arabidopsis exhibited the same performance, showing the conserved role of 2-Cys peroxiredoxins in salt tolerance in plants. TaBAS1 overexpression enhanced the grain yield of wheat under salt stress but not the control condition, not imposing the trade-offs between yield and tolerance. Thus, TaBAS1 could be used for molecular breeding of wheat with superior salt tolerance.

Reactive oxygen species-related genes participate in resistance to cucumber green mottle mosaic virus infection regulated by boron in Nicotiana benthamiana and watermelon

Cucumber green mottle mosaic virus (CGMMV) infection causes acidification and rot of watermelon flesh, resulting in serious economic losses. It is widely reported the interaction relationship between boron and reactive oxygen species (ROS) in regulating normal growth and disease resistance in plants. Our previous results demonstrated that exogenous boron could improve watermelon resistance to CGMMV infection. However, the roles of ROS-related genes regulated by boron in resistance to CGMMV infection are unclear. Here, we demonstrated that CGMMV symptoms were alleviated, and viral accumulations were decreased by boron application in Nicotiana benthamiana, indicating that boron contributed to inhibiting CGMMV infection. Meanwhile, we found that a number of differentially expressed genes (DEGs) associated with inositol biosynthesis, ethylene synthesis, Ca²⁺ signaling transduction and ROS scavenging system were up-regulated, while many DEGs involved in ABA catabolism, GA signal transduction and ascorbic acid metabolism were down-regulated by boron application under CGMMV infection. Additionally, we individually silenced nine ROS-related genes to explore their anti-CGMMV roles using a tobacco rattle virus (TRV) vector. The results showed that NbCat1, NbGME1, NbGGP and NbPrx Q were required for CGMMV infection, while NbGST and NbIPS played roles in resistance to CGMMV infection. The similar results were obtained in watermelon by silencing of ClCat, ClPrx or ClGST expression using a pV190 vector. This study proposed a new strategy for improving plant resistance to CGMMV infection by boron-regulated ROS pathway and provided several target genes for watermelon disease resistance breeding.

Effect of protopine exposure on the physiology and gene expression in the bloom-forming cyanobacterium Microcystis aeruginosa

Environment-friendly sound measures with high algal growth inhibition efficiency are required to control and eliminate CyanoHABs. This study examined the effects of protopine on growth, gene expression, and antioxidant system of the M. aeruginosa TY001 and explored possible damage mechanism. The results revealed that higher concentrations of protopine seriously inhibited the growth of M. aeruginosa. Quantitative real-time PCR analysis showed downregulated expression of stress response genes (prx and fabZ), and DNA repair gene (recA) on days 3 and 5. The activities of antioxidant enzymes were also decreased markedly, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). Additionally, protopine stress can significantly increase the malondialdehyde (MDA) level in cells. In conclusion, oxidative damage and DNA damage are the main mechanisms of protopine inhibition on M. aeruginosa TY001. Our studies provide evidence that alkaloid compounds such as protopine may have a potential use value as components of aquatic management strategies.

Wheat 2-Cys peroxiredoxin plays a dual role in chlorophyll biosynthesis and adaptation to high temperature

The molecular mechanism of high-temperature stress (HTS) response, in plants, has so far been investigated using transcriptomics, while the dynamics of HTS-responsive proteome remain unexplored. We examined the adaptive responses of the resilient wheat cultivar 'Unnat Halna' and dissected the HTS-responsive proteome landscape. This led to the identification of 55 HTS-responsive proteins (HRPs), which are predominantly involved in metabolism and defense pathways. Interestingly, HRPs included a 2-cysteine peroxiredoxin (2CP), designated Ta2CP, presumably involved in stress perception and adaptation. Complementation of Ta2CP in yeast and heterologous expression in Arabidopsis demonstrated its role in thermotolerance. Both Ta2CP silencing and overexpression inferred the involvement of Ta2CP in plant growth and chlorophyll biosynthesis. We demonstrated that Ta2CP interacts with protochlorophyllide reductase b, TaPORB. Reduced TaPORB expression was found in Ta2cp-silenced plants, while upregulation was observed in Ta2CP-overexpressed plants. Furthermore, the downregulation of Ta2CP in Taporb-silenced plants and reduction of protochlorophyllide in Ta2cp-silenced plants suggested the key role of Ta2CP in chlorophyll metabolism. Additionally, the transcript levels of AGPase1 and starch were increased in Ta2cp-silenced plants. More significantly, HTS-treated Ta2cp-silenced plants showed adaptive responses despite increased reactive oxygen species and peroxide concentrations, which might help in rapid induction of high-temperature acclimation.

A 2-Cys peroxiredoxin gene from Tamarix hispida improved salt stress tolerance in plants

BACKGROUND

Peroxiredoxins (Prxs) are a large family of antioxidant enzymes that respond to biotic and abiotic stress by decomposing reactive oxygen species (ROS). In this study, the stress tolerance function of the Th2CysPrx gene was further analysed. It lays a foundation for further studies on the salt tolerance molecular mechanism of T. hispida and improved salt tolerance via transgenic plants.

RESULTS

In this study, the stress tolerance function of the Th2CysPrx gene was further analysed. The results of transgenic tobacco showed higher seed germination rates, root lengths, and fresh weight under salt stress than wild-type tobacco. Simultaneously, physiological indicators of transgenic tobacco and T. hispida showed that Th2CysPrx improved the activities of antioxidant enzymes and enhanced ROS removal ability to decrease cellular damage under salt stress. Moreover, Th2CysPrx improved the expression levels of four antioxidant genes (ThGSTZ1, ThGPX, ThSOD and ThPOD).

CONCLUSIONS

Overall, these results suggested that Th2CysPrx enhanced the salt tolerance of the transgenic plants. These findings lay a foundation for further studies on the salt tolerance molecular mechanism of T. hispida and improved salt tolerance via transgenic plants.

Optimization and standardization of transient expression assays for gene functional analyses in strawberry fruits

Strawberry is increasingly used as a model plant for research on fruit growth and development. The transient gene manipulation (TGM) technique is widely used to determine the function of plant genes, including those in strawberry fruits. However, its reliable application for the precise identification of gene function has been difficult owing to the lack of conditional optimization. In this study, we found that successful transient gene manipulation requires optimization, with the vector type, temperature, and fruit developmental stage being three major factors determining success. Notably, we found that transient gene manipulation was feasible only from the large green fruit stage onwards, making it especially suitable for identifying genes involved in strawberry fruit ripening. Furthermore, we established a method called percentage difference of phenotype (PDP), in which the functional effect of a gene could be precisely and efficiently identified in strawberry fruits. This method can be used to estimate the functional effect of a gene as a value from 0 to 100%, such that different genes can be quantitatively compared for their relative abilities to regulate fruit ripening. This study provides a useful tool for accelerating research on the molecular basis of strawberry fruit ripening.

Differential effects of a post-anthesis heat stress on wheat (Triticum aestivum L.) grain proteome determined by iTRAQ

Heat stress, a major abiotic stressor of wheat (Triticum aestivum L.), often results in reduced yield and decreased quality. In this study, a proteomic method, Tags for Relative and Absolute Quantitation Isobaric (iTRAQ), was adopted to analyze the protein expression profile changes among wheat cultivar Jing411 under heat stress. Results indicated that there were 256 different proteins expressed in Jing411 under heat stress. According to the result of gene annotation and functional classification, 239 proteins were annotated by 856 GO function entries, including growth and metabolism proteins, energy metabolism proteins, processing and storage proteins, defense-related proteins, signal transduction, unknown function proteins and hypothetical proteins. GO enrichment analysis suggested that the differentially expressed proteins in Jing411 under heat stress were mainly involved in stimulus response (67), abiotic stress response (26) and stress response (58), kinase activity (12), and transferase activity (12). Among the differentially expressed proteins in Jing411, 115 were attributed to 119 KEGG signaling/metabolic pathways. KEGG pathway enrichment analysis in Jing411 showed that heat stress mainly affected the starch and sucrose metabolism as well as protein synthesis pathway in the endoplasmic reticulum. The protein interaction network indicated that there were 8 differentially expressed proteins that could form an interaction network in Jing411.

Effect of high-doses pyrogallol on oxidative damage, transcriptional responses and microcystins synthesis in Microcystis aeruginosa TY001 (Cyanobacteria)

Severe eutrophication and harmful cyanobacterial blooms of freshwater ecosystems is a persistent environmental topic in recent decades. Pyrogallol (polyphenol) was confirmed to exhibit one of the most intensive inhibitory effects on the Microcystis aeruginosa. In this study, the expression of genes, release of microcystins (MCs) and antioxidant system of pyrogallol on Microcystis aeruginosa TY001 were investigated. The results revealed that the expression of stress response genes (prx, ftsH, grpE and fabZ) and DNA repair genes (recA and gyrB) were up-regulated. Meanwhile, the antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity, were increased, and the stress caused lipid peroxidation to occur and malondialdehyde (MDA) levels to change. Unexpectedly, the relative transcript abundance of microcystin synthesis genes (mcyB, mcyD and ntcA) and the contents of microcystins (MCs) significantly increased compared with the control in the culture medium. In conclusion, oxidative damage and DNA damage are the primary mechanisms for the allelopathic effect of pyrogallol on M. aeruginosa TY001.

Interactions between 2-Cys peroxiredoxins and ascorbate in autophagosome formation during the heat stress response in Solanum lycopersicum

2-Cys peroxiredoxins (2-CPs) function in the removal of hydrogen peroxide and lipid peroxides but their precise roles in the induction of autophagy have not been characterized. Here we show that heat stress, which is known to induce oxidative stress, leads to the simultaneous accumulation of transcripts encoding 2-CPs and autophagy proteins, as well as autophagosomes, in tomato (Solanum lycopersicum) plants. Virus-induced gene silencing of the tomato peroxiredoxin genes 2-CP1, 2-CP2, and 2-CP1/2 resulted in an increased sensitivity of tomato plants to heat stress. Silencing 2-CP2 or 2-CP1/2 increased the levels of transcripts associated with ascorbate biosynthesis but had no effect on the glutathione pool in the absence of stress. However, the heat-induced accumulation of transcripts associated with the water-water cycle was compromised by the loss of 2-CP1/2 functions. The transcript levels of autophagy-related genes ATG5 and ATG7 were higher in plants with impaired 2-CP1/2 functions, and the formation of autophagosomes increased, together with an accumulation of oxidized and insoluble proteins. Silencing of ATG5 or ATG7 increased the levels of 2-CP transcripts and protein but decreased heat stress tolerance. These results demonstrate that 2-CPs fulfil a pivotal role in heat stress tolerance in tomato, via interactions with ascorbate-dependent pathways and autophagy.