ROS of Distinct Sources and Salicylic Acid Separate Elevated CO2-Mediated Stomatal Movements in Arabidopsis

Dressed Up to the Nines: The Interplay of Phytohormones Signaling and Redox Metabolism During Plant Response to Drought

Plants must effectively respond to various environmental stimuli to achieve optimal growth. This is especially relevant in the context of climate change, where drought emerges as a major factor globally impacting crops and limiting overall yield potential. Throughout evolution, plants have developed adaptative strategies for environmental stimuli, with plant hormones and reactive oxygen species (ROS) playing essential roles in their development. Hormonal signaling and the maintenance of ROS homeostasis are interconnected, playing indispensable roles in growth, development, and stress responses and orchestrating diverse molecular responses during environmental adversities. Nine principal classes of phytohormones have been categorized: auxins, brassinosteroids, cytokinins, and gibberellins primarily oversee developmental growth regulation, while abscisic acid, ethylene, jasmonic acid, salicylic acid, and strigolactones are the main orchestrators of environmental stress responses. Coordination between phytohormones and transcriptional regulation is crucial for effective plant responses, especially in drought stress. Understanding the interplay of ROS and phytohormones is pivotal for elucidating the molecular mechanisms involved in plant stress responses. This review provides an overview of the intricate relationship between ROS, redox metabolism, and the nine different phytohormones signaling in plants, shedding light on potential strategies for enhancing drought tolerance for sustainable crop production.

Novel Insight into the Prevention and Therapeutic Treatment of Paulownia Witches' Broom: A Study on the Effect of Salicylic Acid on Disease Control and the Changes in the Paulownia Transcriptome and Proteome

Paulownia species not only have significant economic benefits but also show great potential in ecological conservation. However, they are highly susceptible to phytoplasma infections, causing Paulownia witches' broom (PaWB), which severely restricts the development of the Paulownia industry. Salicylic acid (SA) plays a crucial role in plant disease resistance. However, there have been no reports on the effect of SA on PaWB. Due to the properties of SA, it may have potential in controlling PaWB. Based on the above speculation, the prevention and therapeutic effect of SA on PaWB and its effect on the PaWB-infected Paulownia transcriptome and proteome were studied in this work. The results indicated that 0.1 mmol/L was the optimal SA concentration for inhibiting the germination of Paulownia axillary buds. In terms of resistance physiological indicators, SA treatment significantly affected both Paulownia tomentosa infected (PTI) seedlings and Paulownia fortunei infected (PFI) seedlings, where the activities of peroxidase (POD) and superoxide dismutase (SOD) were enhanced. Malondialdehyde (MDA), O2-, and H2O2, however, were significantly reduced. Specifically, after SA treatment, SOD activity increased by 28% in PFI and 25% in PTI, and POD activity significantly increased by 61% in PFI and 58% in PTI. Moreover, the MDA content decreased by 30% in PFI and 23% in PTI, the H2O2 content decreased by 26% in PFI and 19% in PTI, and the O2- content decreased by 21% in PFI and 19% in PTI. Transcriptomic analysis showed that there were significant upregulations of MYB, NAC, and bHLH and other transcription factors after SA treatment. Moreover, genes involved in PaWB-related defense responses such as RAX2 also showed significant differences. Furthermore, proteomic analysis indicated that after SA treatment, proteins involved in signal transduction, protein synthesis modification, and disease defense were differentially expressed. This work provides a research foundation for the prevention and treatment of PaWB and offers references for exploring anti-PaWB methods.

BIG coordinates auxin and SHORT ROOT to promote asymmetric stem cell divisions in Arabidopsis roots

KEY MESSAGE

BIG regulates ground tissue formative divisions by bridging the auxin gradient with SHR abundance in Arabidopsis roots. The formative divisions of cortex/endodermis initials (CEIs) and CEI daughter cells (CEIDs) in Arabidopsis roots are coordinately controlled by the longitudinal auxin gradient and the radial SHORT ROOT (SHR) abundance. However, the mechanism underlying this coordination remains poorly understood. In this study, we demonstrate that BIG regulates ground tissue formative divisions by bridging the auxin gradient with SHR abundance. Mutations in BIG gene repressed cell cycle progression, delaying the formative divisions within the ground tissues and impairing the establishment of endodermal and cortical identities. In addition, we uncovered auxin's suppressive effect on BIG expression, triggering CYCLIND6;1 (CYCD6;1) activation in an SHR-dependent fashion. Moreover, the degradation of RETINOBLASTOMA-RELATED (RBR) is jointly regulated by BIG and CYCD6;1. The loss of BIG function led to RBR protein accumulation, detrimentally impacting the SHR/SCARECROW (SCR) protein complex and the CEI/CEID formative divisions. Collectively, these findings shed light on a fundamental mechanism wherein BIG intricately coordinates the interplay between SHR/SCR and auxin, steering ground tissue patterning within Arabidopsis root tissue.

Physiological and Proteomic Responses of the Tetraploid Robinia pseudoacacia L. to High CO2 Levels

The increase in atmospheric CO2 concentration is a significant factor in triggering global warming. CO2 is essential for plant photosynthesis, but excessive CO2 can negatively impact photosynthesis and its associated physiological and biochemical processes. The tetraploid Robinia pseudoacacia L., a superior and improved variety, exhibits high tolerance to abiotic stress. In this study, we investigated the physiological and proteomic response mechanisms of the tetraploid R. pseudoacacia under high CO2 treatment. The results of our physiological and biochemical analyses revealed that a 5% high concentration of CO2 hindered the growth and development of the tetraploid R. pseudoacacia and caused severe damage to the leaves. Additionally, it significantly reduced photosynthetic parameters such as Pn, Gs, Tr, and Ci, as well as respiration. The levels of chlorophyll (Chl a and b) and the fluorescent parameters of chlorophyll (Fm, Fv/Fm, qP, and ETR) also significantly decreased. Conversely, the levels of ROS (H2O2 and O2·-) were significantly increased, while the activities of antioxidant enzymes (SOD, CAT, GR, and APX) were significantly decreased. Furthermore, high CO2 induced stomatal closure by promoting the accumulation of ROS and NO in guard cells. Through a proteomic analysis, we identified a total of 1652 DAPs after high CO2 treatment. GO functional annotation revealed that these DAPs were mainly associated with redox activity, catalytic activity, and ion binding. KEGG analysis showed an enrichment of DAPs in metabolic pathways, secondary metabolite biosynthesis, amino acid biosynthesis, and photosynthetic pathways. Overall, our study provides valuable insights into the adaptation mechanisms of the tetraploid R. pseudoacacia to high CO2.

Integrative regulatory mechanisms of stomatal movements under changing climate

Global climate change-caused drought stress, high temperatures and other extreme weather profoundly impact plant growth and development, restricting sustainable crop production. To cope with various environmental stimuli, plants can optimize the opening and closing of stomata to balance CO2 uptake for photosynthesis and water loss from leaves. Guard cells perceive and integrate various signals to adjust stomatal pores through turgor pressure regulation. Molecular mechanisms and signaling networks underlying the stomatal movements in response to environmental stresses have been extensively studied and elucidated. This review focuses on the molecular mechanisms of stomatal movements mediated by abscisic acid, light, CO2 , reactive oxygen species, pathogens, temperature, and other phytohormones. We discussed the significance of elucidating the integrative mechanisms that regulate stomatal movements in helping design smart crops with enhanced water use efficiency and resilience in a climate-changing world.

Salicylic acid and jasmonic acid in elevated CO2-induced plant defense response to pathogens

Plants respond to elevated CO₂ (eCO₂) via a variety of signaling pathways that often rely on plant hormones. In particular, phytohormone salicylic acid (SA) and jasmonic acid (JA) play a key role in plant defense against diverse pathogens at eCO₂. eCO₂ affects the synthesis and signaling of SA and/or JA and variations in SA and JA signaling lead to variations in plant defense responses to pathogens. In general, eCO₂ promotes SA signaling and represses the JA pathway, and thus diseases caused by biotrophic and hemibiotrophic pathogens are typically suppressed, while the incidence and severity of diseases caused by necrotrophic fungal pathogens are enhanced under eCO₂ conditions. Moreover, eCO₂-induced modulation of antagonism between SA and JA leads to altered plant immunity to different pathogens. Notably, research in this area has often yielded contradictory findings and these responses vary depending on plant species, growth conditions, photoperiod, and fertilizer management. In this review, we focus on the recent advances in SA, and JA signaling pathways in plant defense and their involvement in plant immune responses to pathogens under eCO₂. Since atmospheric CO₂ will continue to increase, it is crucial to further explore how eCO₂ may alter plant defense and host-pathogen interactions in the context of climate change in both natural as well as agricultural ecosystems.

Hydrogen sulfide signaling in plants

SIGNIFICANCE

Hydrogen sulfide (H2S) is a multitasking potent regulator that facilitates plant growth, development, and responses to environmental stimuli.

RECENT ADVANCES

The important beneficial effects of H2S in various aspects of plant physiology aroused the interest of this chemical for agriculture. Protein cysteine persulfidation has been recognized as the main redox regulatory mechanism of H2S signaling. An increasing number of studies, including large-scale proteomic analyses and function characterizations, have revealed that H2S-mediated persulfidations directly regulate protein functions, altering downstream signaling in plants. To date, the importance of H2S-mediated persufidation in several abscisic acid signaling-controlling key proteins has been assessed as well as their role in stomatal movements, largely contributing to the understanding of the plant H2S-regulatory mechanism.

CRITICAL ISSUES

The molecular mechanisms of the H2S sensing and transduction in plants remain elusive. The correlation between H2S-mediated persulfidation with other oxidative posttranslational modifications of cysteines are still to be explored.

FUTURE DIRECTIONS

Implementation of advanced detection approaches for the spatiotemporal monitoring of H2S levels in cells and the current proteomic profiling strategies for the identification and quantification of the cysteine site-specific persulfidation will provide insight into the H2S signaling in plants.

Morpho-Physiological and Hormonal Response of Winter Wheat Varieties to Drought Stress at Stem Elongation and Anthesis Stages

Drought stress can significantly reduce wheat growth and development as well as grain yield. This study investigated morpho-physiological and hormonal (abscisic (ABA) and salicylic (SA) acids) responses of six winter wheat varieties during stem elongation and anthesis stage as well grain yield-related traits were measured after harvest. To examine drought response, plants were exposed to moderate non-lethal drought stress by withholding watering for 45 and 65% of the volumetric soil moisture content (VSMC) for 14 days at separate experiments for each of those two growth stages. During the stem elongation phase, ABA was increased, confirming the stress status of plants, and SA showed a tendency to increase, suggesting their role as stress hormones in the regulation of stress response, such as the increase in the number of leaves and tillers in drought stress conditions, and further keeping turgor pressure and osmotic adjustment in leaves. At the anthesis stage, heavier drought stress resulted in ABA accumulation in flag leaves that generated an integrated response of maturation, where ABA was not positively correlated with any of investigated traits. After harvest, the variety Bubnjar, followed by Pepeljuga and Anđelka, did not significantly decrease the number of grains per ear and 1000 kernel weight (except Anđelka) in drought treatments, thus, declaring them more tolerant to drought. On the other hand, Rujana, Fifi, and particularly Silvija experienced the highest reduction in grain yield-related traits, considering them drought-sensitive varieties.

Climate change impedes plant immunity mechanisms

Rapid climate change caused by human activity is threatening global crop production and food security worldwide. In particular, the emergence of new infectious plant pathogens and the geographical expansion of plant disease incidence result in serious yield losses of major crops annually. Since climate change has accelerated recently and is expected to worsen in the future, we have reached an inflection point where comprehensive preparations to cope with the upcoming crisis can no longer be delayed. Development of new plant breeding technologies including site-directed nucleases offers the opportunity to mitigate the effects of the changing climate. Therefore, understanding the effects of climate change on plant innate immunity and identification of elite genes conferring disease resistance are crucial for the engineering of new crop cultivars and plant improvement strategies. Here, we summarize and discuss the effects of major environmental factors such as temperature, humidity, and carbon dioxide concentration on plant immunity systems. This review provides a strategy for securing crop-based nutrition against severe pathogen attacks in the era of climate change.

Nitric oxide: A core signaling molecule under elevated GHGs (CO2, CH4, N2O, O3)-mediated abiotic stress in plants

Nitric oxide (NO), an ancient molecule with multiple roles in plants, has gained momentum and continues to govern plant biosciences-related research. NO, known to be involved in diverse physiological and biological processes, is a central molecule mediating cellular redox homeostasis under abiotic and biotic stresses. NO signaling interacts with various signaling networks to govern the adaptive response mechanism towards stress tolerance. Although diverging views question the role of plants in the current greenhouse gases (GHGs) budget, it is widely accepted that plants contribute, in one way or another, to the release of GHGs (carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and ozone (O3)) to the atmosphere, with CH4 and N2O being the most abundant, and occur simultaneously. Studies support that elevated concentrations of GHGs trigger similar signaling pathways to that observed in commonly studied abiotic stresses. In the process, NO plays a forefront role, in which the nitrogen metabolism is tightly related. Regardless of their beneficial roles in plants at a certain level of accumulation, high concentrations of CO2, CH4, and N2O-mediating stress in plants exacerbate the production of reactive oxygen (ROS) and nitrogen (RNS) species. This review assesses and discusses the current knowledge of NO signaling and its interaction with other signaling pathways, here focusing on the reported calcium (Ca2+) and hormonal signaling, under elevated GHGs along with the associated mechanisms underlying GHGs-induced stress in plants.

BIG Modulates Stem Cell Niche and Meristem Development via SCR/SHR Pathway in Arabidopsis Roots

BIG, a regulator of polar auxin transport, is necessary to regulate the growth and development of Arabidopsis. Although mutations in the BIG gene cause severe root developmental defects, the exact mechanism remains unclear. Here, we report that disruption of the BIG gene resulted in decreased quiescent center (QC) activity and columella cell numbers, which was accompanied by the downregulation of WUSCHEL-RELATED HOMEOBOX5 (WOX5) gene expression. BIG affected auxin distribution by regulating the expression of PIN-FORMED proteins (PINs), but the root morphological defects of big mutants could not be rescued solely by increasing auxin transport. Although the loss of BIG gene function resulted in decreased expression of the PLT1 and PLT2 genes, genetic interaction assays indicate that this is not the main reason for the root morphological defects of big mutants. Furthermore, genetic interaction assays suggest that BIG affects the stem cell niche (SCN) activity through the SCRSCARECROW (SCR)/SHORT ROOT (SHR) pathway and BIG disruption reduces the expression of SCR and SHR genes. In conclusion, our findings reveal that the BIG gene maintains root meristem activity and SCN integrity mainly through the SCR/SHR pathway.

Stomatal responses to carbon dioxide and light require abscisic acid catabolism in Arabidopsis

In plants, stomata control water loss and CO₂ uptake. The aperture and density of stomatal pores, and hence the exchange of gases between the plant and the atmosphere, are controlled by internal factors such as the plant hormone abscisic acid (ABA) and external signals including light and CO₂. In this study, we examine the importance of ABA catabolism in the stomatal responses to CO₂ and light. By using the ABA 8'-hydroxylase-deficient Arabidopsis thaliana double mutant cyp707a1 cyp707a3, which is unable to break down and instead accumulates high levels of ABA, we reveal the importance of the control of ABA concentration in mediating stomatal responses to CO₂ and light. Intriguingly, our experiments suggest that endogenously produced ABA is unable to close stomata in the absence of CO₂. Furthermore, we show that when plants are grown in short day conditions ABA breakdown is required for the modulation of both elevated [CO₂]-induced stomatal closure and elevated [CO₂]-induced reductions in leaf stomatal density. ABA catabolism is also required for the stomatal density response to light intensity, and for the full range of light-induced stomatal opening, suggesting that ABA catabolism is critical for the integration of stomatal responses to a range of environmental stimuli.

Elevated CO2 and Reactive Oxygen Species in Stomatal Closure

Plant guard cell is essential for photosynthesis and transpiration. The aperture of stomata is sensitive to various environment factors. Carbon dioxide (CO₂) is an important regulator of stomatal movement, and its signaling includes the perception, transduction and gene expression. The intersections with many other signal transduction pathways make the regulation of CO₂ more complex. High levels of CO₂ trigger stomata closure, and reactive oxygen species (ROS) as the key component has been demonstrated function in this regulation. Additional research is required to understand the underlying molecular mechanisms, especially for the detailed signal factors related with ROS in this response. This review focuses on Arabidopsis stomatal closure induced by high-level CO₂, and summarizes current knowledge of the role of ROS involved in this process.