Phytochrome B regulates reactive oxygen signaling during abiotic and biotic stress in plants

Microwave pre-stimulation methodology for plant growth promotion

Although positive effects of microwave irradiation on plants have been reported, their underlying mechanisms remain unknown. In this study, we investigated the effects of low microwave irradiation on Arabidopsis thaliana. Interestingly, we found low output (23 W) with oscillating condition (not continuous irradiation) promoted plant growth. The microwave irradiation neither raised the plants' temperature nor induced heat responsive gene expression. Furthermore, overall transcriptome profile in microwave irradiation treated plants were significantly different from heat treated plants, suggesting that growth promotion might be attributed to non-thermal effects of microwave. Transcriptome and metabolome analysis indicated that microwave irradiation altered circadian clock as well as hormonal response especially in auxin and gibberellin, which promoted plant growth by inducing amino acid biosynthesis and stress tolerance, and reducing cell wall thickness. This finding potentially contributes to develop new approach to increase food production through accelerating crop yield in environmentally friendly way.

Photoreceptors Are Involved in Antioxidant Effects of Melatonin Under High Light in Arabidopsis

The beneficial role of melatonin (MT) as a potent broad-spectrum antioxidant and hormone-like regulator in plant protection against adverse environmental conditions is indisputable. However, the molecular networks underlying its unique scavenging capabilities are still far from understood. Herein, we show the ability of MT to maintain physiological functions under high light stress (HL) is mediated by photoreceptors. Melatonin treatment (50 μM) of the photoreceptor mutants phyA/B and cry1/2 augmented the deleterious effects of excess light (600 μmol m-2 s-1, 24 h), as evidenced by increased TBARs levels and electrolyte leakage, as well as decreased photosynthetic efficiency, in contrast to their parental form, Landsberg erecta, in which these parameters were significantly improved. The reduced stress resistance of the mutants was also confirmed by analysis of the transcript accumulation of ROS markers and enzymatic scavengers. Moreover, the increase in melatonin content in the mutants exposed to HL + MT contributed to increased ROS accumulation; therefore, the deleterious effect of MT could not be explained by an imbalance in ROS production below the cytostatic level. We hypothesize that the light-sensitive phenotypes of photoreceptor mutants under MT treatment may be due to the misregulation of stress-related genes that are targets for melatonin action.

Useful or merely convenient: can enzymatic antioxidant activity be used as a proxy for abiotic stress tolerance?

During their lifespan, plants are often exposed to a broad range of stresses that change their redox balance and lead to accumulation of reactive oxygen species (ROS). The traditional view is that this comes with negative consequences to cells structural integrity and metabolism and, to prevent this, plants evolved a complex and well-coordinated antioxidant defence system that relies on the operation of a range of enzymatic and non-enzymatic antioxidants (AO). Due to the simplicity of measuring their activity, and in light of the persistent dogma that stress-induced ROS accumulation is detrimental for plants, it is not surprising that enzymatic AOs have often been advocated as suitable proxies for stress tolerance as well as potential targets for improving tolerance traits. However, there are a growing number of reports showing either no changes or even down-regulation of AO systems in stressed plants. Moreover, ROS are recognized now as important second messengers operating in both local and systemic signalling, synergistically interacting with the primary stressor, to regulate gene expression needed for optimal acclimatization. This work critically assesses the suitability of using enzymatic AOs as a proxy for stress tolerance or as a target for crop genetic improvement. It is concluded that constitutively higher AO activity may interfere with stress-induced ROS signalling and be a disadvantage for plant stress tolerance.

Combination of maleic hydrazide and coumarin inhibits rice seed germination involving reactive oxygen species accumulation, ABA metabolism and starch degradation

Pre-harvest sprouting (PHS) in cereal crops is a prevalent phenomenon that impacts grain yield and quality. Several PHS inhibitory compounds were screened and identified in previous studies, such as eugenol (EUG), maleic hydrazide (MH), coumarin (COU), etc. However, few studies have focused on the combination of PHS inhibitors, and the inhibitory mechanism remains unclear. Here, through combination tests of EUG, MH, and COU, the optimal combination of PHS inhibitors was selected as MH 20 mg L-1 + COU 100 mg L-1, which presented the lowest germination percentages. The optimal combination treatment significantly decreased the germination rate, α-amylase activity, content of soluble sugar and soluble protein, enhanced ABA content and the activity of superoxide dismutase (SOD) and peroxidase (POD), inhibited the production of superoxide anion (O2-) and hydrogen peroxide, and reduced the content of malondialdehyde (MDA); conversely, this trend is precisely the opposite in normal germination. Furthermore, gene expression analysis revealed that the optimal combination of MH and COU significantly decreased the expression level of OsAmy1A and OsAmy3D at 12 and 48 h after imbibition (HAI); and promoted the expression of OsRbohs (OsRbohA, OsRbohC, OsRbohD, OsRbohE, OsRbohH) and ABA biosynthetic genes OsNCED1, OsNCED2, and OsNCED5, especially OsNCED2 at 12 HAI, but down-regulated expression of OsRbohs and ABA catabolic genes OsABA8ox1-3 at 48 HAI. These results demonstrated that the delay in seed germination induced by MH and COU involved in ROS, ABA, and sugars; the optimal combination of MH and COU inhibited the germination process by promoting ABA biosynthesis and reducing ABA catabolism, and restraining the α-amylase activity to lower soluble sugar content. Intriguingly, although the expression of OsRbohs, which play a crucial role in generating ROS, increased in early imbibition (12h), the activity of the antioxidant enzymes SOD and POD also increased with the optimal combination treatment of MH and COU, which lead to the delay in ROS accumulation and inhibition of germination. These results have deepened our understanding of the regulatory mechanism of PHS inhibitors and provided theoretical support for the application of MH and COU in preventing sprouting before crop harvesting.

Shade-induced ROS/NO reinforce COP1-mediated diffuse cell growth

Canopy shade enhances the activity of PHYTOCHROME INTERACTING FACTORs (PIFs) to boost auxin synthesis in the cotyledons. Auxin, together with local PIFs and their positive regulator CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), promotes hypocotyl growth to facilitate access to light. Whether shade alters the cellular redox status thereby affecting growth responses, remains unexplored. Here, we show that, under shade, high auxin levels increased reactive oxygen species and nitric oxide accumulation in the hypocotyl of Arabidopsis. This nitroxidative environment favored the promotion of hypocotyl growth by COP1 under shade. We demonstrate that COP1 is S-nitrosylated, particularly under shade. Impairing this redox regulation enhanced COP1 degradation by the proteasome and diminished the capacity of COP1 to interact with target proteins and to promote hypocotyl growth. Disabling this regulation also generated transversal asymmetries in hypocotyl growth, indicating poor coordination among different cells, which resulted in random hypocotyl bending and predictably low ability to compete with neighbors. These findings highlight the significance of redox signaling in the control of diffuse growth during shade avoidance.

Probing plant signal processing optogenetically by two channelrhodopsins

Early plant responses to different stress situations often encompass cytosolic Ca2+ increases, plasma membrane depolarization and the generation of reactive oxygen species1-3. However, the mechanisms by which these signalling elements are translated into defined physiological outcomes are poorly understood. Here, to study the basis for encoding of specificity in plant signal processing, we used light-gated ion channels (channelrhodopsins). We developed a genetically engineered channelrhodopsin variant called XXM 2.0 with high Ca2+ conductance that enabled triggering cytosolic Ca2+ elevations in planta. Plant responses to light-induced Ca2+ influx through XXM 2.0 were studied side by side with effects caused by an anion efflux through the light-gated anion channelrhodopsin ACR1 2.04. Although both tools triggered membrane depolarizations, their activation led to distinct plant stress responses: XXM 2.0-induced Ca2+ signals stimulated production of reactive oxygen species and defence mechanisms; ACR1 2.0-mediated anion efflux triggered drought stress responses. Our findings imply that discrete Ca2+ signals and anion efflux serve as triggers for specific metabolic and transcriptional reprogramming enabling plants to adapt to particular stress situations. Our optogenetics approach unveiled that within plant leaves, distinct physiological responses are triggered by specific ion fluxes, which are accompanied by similar electrical signals.

Functional analysis of reactive oxygen species-driven stress systemic signalling, interplay and acclimation

Reactive oxygen species (ROS) play a critical role in plant development and stress responses, acting as key components in rapid signalling pathways. The 'ROS wave' triggers essential acclimation processes, ultimately ensuring plant survival under diverse challenges. This review explores recent advances in understanding the composition and functionality of the ROS wave within plant cells. During their initiation and propagation, ROS waves interact with other rapid signalling pathways, hormones and various molecular compounds. Recent research sheds light on the intriguing lack of a rigid hierarchy governing these interactions, highlighting a complex interplay between diverse signals. Notably, ROS waves culminate in systemic acclimation, a crucial outcome for enhanced stress tolerance. This review emphasizes the versatility of ROS, which act as flexible players within a network of short- and long-term factors contributing to plant stress resilience. Unveiling the intricacies of these interactions between ROS and various signalling molecules holds immense potential for developing strategies to augment plant stress tolerance, contributing to improved agricultural practices and overall ecosystem well-being.

Redox regulation of chromatin remodelling in plants

Changes in the cellular redox balance that occur during plant responses to unfavourable environmental conditions significantly affect a myriad of redox-sensitive processes, including those that impact on the epigenetic state of the chromatin. Various epigenetic factors, like histone modifying enzymes, chromatin remodelers, and DNA methyltransferases can be targeted by oxidative posttranslational modifications. As their combined action affects the epigenetic regulation of gene expression, they form an integral part of plant responses to (a)biotic stress. Epigenetic changes triggered by unfavourable environmental conditions are intrinsically linked with primary metabolism that supplies intermediates and donors, such acetyl-CoA and S-adenosyl-methionine, that are critical for the epigenetic decoration of histones and DNA. Here, we review the recent advances in our understanding of redox regulation of chromatin remodelling, dynamics of epigenetic marks, and the interplay between epigenetic control of gene expression, redox signalling and primary metabolism within an (a)biotic stress context.

ROS are universal cell-to-cell stress signals

The interplay between reactive oxygen species (ROS) and the redox state of cells is deeply rooted in the biology of almost all organisms, regulating development, growth, and responses to the environment. Recent studies revealed that the ROS levels and redox state of one cell can be transmitted, as an information 'state' or 'currency', to other cells and spread by cell-to-cell communication within an entire community of cells or an organism. Here, we discuss the different pathways that mediate cell-to-cell signaling in plants, their hierarchy, and the different mechanisms that transmit ROS/redox signaling between different cells. We further hypothesize that ROS/redox signaling between different organisms could play a key role within the 'one world' principle, impacting human health and our future.

Application of Multi-Omics Technologies to the Study of Phytochromes in Plants

Phytochromes (phy) are distributed in various plant organs, and their physiological effects influence plant germination, flowering, fruiting, and senescence, as well as regulate morphogenesis throughout the plant life cycle. Reactive oxygen species (ROS) are a key regulatory factor in plant systemic responses to environmental stimuli, with an attractive regulatory relationship with phytochromes. With the development of high-throughput sequencing technology, omics techniques have become powerful tools, and researchers have used omics techniques to facilitate the big data revolution. For an in-depth analysis of phytochrome-mediated signaling pathways, integrated multi-omics (transcriptomics, proteomics, and metabolomics) approaches may provide the answer from a global perspective. This article comprehensively elaborates on applying multi-omics techniques in studying phytochromes. We describe the current research status and future directions on transcriptome-, proteome-, and metabolome-related network components mediated by phytochromes when cells are subjected to various stimulation. We emphasize the importance of multi-omics technologies in exploring the effects of phytochromes on cells and their molecular mechanisms. Additionally, we provide methods and ideas for future crop improvement.

Identification of NADPH Oxidase Genes Crucial for Rice Multiple Disease Resistance and Yield Traits

Reactive oxygen species (ROS) act as a group of signaling molecules in rice functioning in regulation of development and stress responses. Respiratory burst oxidase homologues (Rbohs) are key enzymes in generation of ROS. However, the role of the nine Rboh family members was not fully understood in rice multiple disease resistance and yield traits. In this study, we constructed mutants of each Rboh genes and detected their requirement in rice multiple disease resistance and yield traits. Our results revealed that mutations of five Rboh genes (RbohA, RbohB, RbohE, RbohH, and RbohI) lead to compromised rice blast disease resistance in a disease nursery and lab conditions; mutations of five Rbohs (RbohA, RbohB, RbohC, RbohE, and RbohH) result in suppressed rice sheath blight resistance in a disease nursery and lab conditions; mutations of six Rbohs (RbohA, RbohB, RbohC, RbohE, RbohH and RbohI) lead to decreased rice leaf blight resistance in a paddy yard and ROS production induced by PAMPs and pathogen. Moreover, all Rboh genes participate in the regulation of rice yield traits, for all rboh mutants display one or more compromised yield traits, such as panicle number, grain number per panicle, seed setting rate, and grain weight, resulting in reduced yield per plant except rbohb and rbohf. Our results identified the Rboh family members involved in the regulation of rice resistance against multiple pathogens that caused the most serious diseases worldwide and provide theoretical supporting for breeding application of these Rbohs to coordinate rice disease resistance and yield traits.

Unravelling molecular mechanisms involved in resistance priming against downy mildew (Plasmopara viticola) in grapevine (Vitis vinifera L.)

Downy mildew (DM; Plasmopara viticola) is amongst the most severe fungal diseases in viticulture and the reason for the majority of fungicide applications. To reduce synthetic and copper-based fungicides, there is an urgent need for natural alternatives, which are being increasingly tested by the industry and the research community. However, their mode of action remains unclear. Therefore, our study aimed to investigate the transcriptomic changes induced by oregano essential oil vapour (OEOV) in DM-infected grapevines. OEOV was applied at different time points before and after DM infection to differentiate between a priming effect and a direct effect. Both pre-DM treatment with OEOV and post-infection treatment resulted in a significant reduction in DM sporulation. RNA-seq, followed by differential gene expression and weighted gene co-expression network analysis, identified co-expressed gene modules associated with secondary metabolism, pathogen recognition and response. Surprisingly, the molecular mechanisms underlying the efficiency of OEOV against DM appear to be independent of stilbene synthesis, and instead involve genes from a putative signalling pathway that has yet to be characterized. This study enhances our understanding of the molecular regulation of innate plant immunity and provides new insights into the mode of action of alternative natural antifungal agents.

Functions of Plant Phytochrome Signaling Pathways in Adaptation to Diverse Stresses

Phytochromes are receptors for red light (R)/far-red light (FR), which are not only involved in regulating the growth and development of plants but also in mediated resistance to various stresses. Studies have revealed that phytochrome signaling pathways play a crucial role in enabling plants to cope with abiotic stresses such as high/low temperatures, drought, high-intensity light, and salinity. Phytochromes and their components in light signaling pathways can also respond to biotic stresses caused by insect pests and microbial pathogens, thereby inducing plant resistance against them. Given that, this paper reviews recent advances in understanding the mechanisms of action of phytochromes in plant resistance to adversity and discusses the importance of modulating the genes involved in phytochrome signaling pathways to coordinate plant growth, development, and stress responses.

Genome-Wide Identification and Characterization of the Phytochrome Gene Family in Peanut

To investigate the potential role of phytochrome (PHY) in peanut growth and its response to environmental fluctuations, eight candidate AhPHY genes were identified via genome-wide analysis of cultivated peanut. These AhPHY polypeptides were determined to possess acidic and hydrophilic physiochemical properties and exhibit subcellular localization patterns consistent with residence in the nucleus and cytoplasm. Phylogenetic analysis revealed that the AhPHY gene family members were classified into three subgroups homologous to the PHYA/B/E progenitors of Arabidopsis. AhPHY genes within the same clade largely displayed analogous gene structure, conserved motifs, and phosphorylation sites. AhPHY exhibited symmetrical distribution across peanut chromosomes, with 7 intraspecific syntenic gene pairs in peanut, as well as 4 and 20 interspecific PHY syntenic gene pairs in Arabidopsis and soybean, respectively. A total of 42 cis-elements were predicted in AhPHY promoters, including elements implicated in phytohormone regulation, stress induction, physiology, and photoresponse, suggesting putative fundamental roles across diverse biological processes. Moreover, spatiotemporal transcript profiling of AhPHY genes in various peanut tissues revealed distinct expression patterns for each member, alluding to putative functional specialization. This study contributes novel insights into the classification, structure, molecular evolution, and expression profiles of the peanut phytochrome gene family, and also provides phototransduction gene resources for further mechanistic characterization.

The Role of Blue and Red Light in the Orchestration of Secondary Metabolites, Nutrient Transport and Plant Quality

Light is a fundamental environmental parameter for plant growth and development because it provides an energy source for carbon fixation during photosynthesis and regulates many other physiological processes through its signaling. In indoor horticultural cultivation systems, sole-source light-emitting diodes (LEDs) have shown great potential for optimizing growth and producing high-quality products. Light is also a regulator of flowering, acting on phytochromes and inducing or inhibiting photoperiodic plants. Plants respond to light quality through several light receptors that can absorb light at different wavelengths. This review summarizes recent progress in our understanding of the role of blue and red light in the modulation of important plant quality traits, nutrient absorption and assimilation, as well as secondary metabolites, and includes the dynamic signaling networks that are orchestrated by blue and red wavelengths with a focus on transcriptional and metabolic reprogramming, plant productivity, and the nutritional quality of products. Moreover, it highlights future lines of research that should increase our knowledge to develop tailored light recipes to shape the plant characteristics and the nutritional and nutraceutical value of horticultural products.

Light-Dependent Regulatory Interactions between the Redox System and miRNAs and Their Biochemical and Physiological Effects in Plants

Light intensity and spectrum play a major role in the regulation of the growth, development, and stress response of plants. Changes in the light conditions affect the formation of reactive oxygen species, the activity of the antioxidants, and, consequently, the redox environment in the plant tissues. Many metabolic processes, thus the biogenesis and function of miRNAs, are redox-responsive. The miRNAs, in turn, can modulate various components of the redox system, and this process is also associated with the alteration in the intensity and spectrum of the light. In this review, we would like to summarise the possible regulatory mechanisms by which the alterations in the light conditions can influence miRNAs in a redox-dependent manner. Daily and seasonal fluctuations in the intensity and spectral composition of the light can affect the expression of miRNAs, which can fine-tune the various physiological and biochemical processes due to their effect on their target genes. The interactions between the redox system and miRNAs may be modulated by light conditions, and the proposed function of this regulatory network and its effect on the various biochemical and physiological processes will be introduced in plants.

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.

Moonlight Is Perceived as a Signal Promoting Genome Reorganization, Changes in Protein and Metabolite Profiles and Plant Growth

Rhythmic exposure to moonlight has been shown to affect animal behavior, but its effects on plants, often observed in lunar agriculture, have been doubted and often regarded as myth. Consequently, lunar farming practices are not well scientifically supported, and the influence of this conspicuous environmental factor, the moon, on plant cell biology has hardly been investigated. We studied the effect of full moonlight (FML) on plant cell biology and examined changes in genome organization, protein and primary metabolite profiles in tobacco and mustard plants and the effect of FML on the post-germination growth of mustard seedlings. Exposure to FML was accompanied by a significant increase in nuclear size, changes in DNA methylation and cleavage of the histone H3 C-terminal region. Primary metabolites associated with stress were significantly increased along with the expression of stress-associated proteins and the photoreceptors phytochrome B and phototropin 2; new moon experiments disproved the light pollution effect. Exposure of mustard seedlings to FML enhanced growth. Thus, our data show that despite the low-intensity light emitted by the moon, it is an important environmental factor perceived by plants as a signal, leading to alteration in cellular activities and enhancement of plant growth.