Redox regulation of meristem quiescence: Outside/ in

Quiescence is an essential property of meristematic cells, which restrains the cell cycle while retaining the capacity to divide. This crucial process not only facilitates life-long tissue homeostasis and regenerative capacity but also provides protection against adverse environmental conditions, enabling cells to conserve the proliferative potency while minimising DNA damage. As a survival attribute, quiescence is inherently regulated by the products of aerobic life, in particular reactive oxygen species (ROS) and the redox (reduction/ oxidation) mechanisms that plant have evolved to channel these into pervasive signals. Adaptive responses allow quiescent cells to compensate for reduced oxygen tension (hypoxia) in a reversible manner, while the regulated production of the superoxide anion (.O2-) facilitates cell division and the maintenance of stem cells. Here we discuss the role of ROS and redox reactions in the control of the quiescent state in plant meristems, and how this process is integrated with cellular energy and hormone biochemistry. We consider the pathways that sense and transmit redox signals with a focus on the central significance of redox regulation in the mitochondria and nucleus, which is a major regulator of quiescence in meristems. We discuss recent studies that suggest ROS are a critical component of the feedback loops that control stem cell identity and fate and suggest that the ROS/hypoxia interface is an important "outside/ in" positional cue for plant cells, particularly in meristems.

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.

Nitric oxide, energy and redox-dependent responses to hypoxia

Hypoxia occurs when the oxygen levels fall below the levels required for mitochondria to support respiration. Regulated hypoxia is associated with quiescence, particularly in storage organs (seeds) and stem cell niches. In contrast, environmentally-induced hypoxia poses significant challenges for metabolically-active cells that are adapted to aerobic respiration. The perception of oxygen availability through cysteine oxidases, which function as oxygen-sensing enzymes in plants that control the N-degron pathway, and the regulation of hypoxia-responsive genes and processes is essential to survival. Functioning together with reactive oxygen species (ROS), particularly hydrogen peroxide and reactive nitrogen species (RNS), such as nitric oxide (•NO), nitrogen dioxide (•NO2), S-nitrosothiols (SNOs), and peroxynitrite (ONOO-), hypoxia signaling pathways trigger anatomical adaptations such as formation of aerenchyma, mobilization of sugar reserves for anaerobic germination, formation of aerial adventitious roots and hyponastic response. NO and hydrogen peroxide (H2O2) participate in local and systemic signaling pathways that facilitate acclimation to changing energetic requirements, controlling glycolytic fermentation, the GABA shunt and amino acid synthesis. NO enhances antioxidant capacity and contributes to the recycling of redox equivalents energy metabolism through the phytoglobin (Pgb)-NO cycle. Here, we summarize current knowledge, highlighting the central role of NO and redox regulation in adaptive responses that prevent hypoxia-induced death in challenging conditions such as flooding.

The MYC2-PUB22-JAZ4 module plays a crucial role in jasmonate signaling in tomato

Jasmonates (JAs), a class of lipid-derived stress hormones, play a crucial role across an array of plant physiological processes and stress responses. Although JA signaling is thought to rely predominantly on the degradation of specific JAZ proteins by SCFCOI1, it remains unclear whether other pathways are involved in the regulation of JAZ protein stability. Here, we report that PUB22, a plant U-box type E3 ubiquitin ligase, plays a critical role in the regulation of plant resistance against Helicoverpa armigera and other JA responses in tomato. Whereas COI1 physically interacts with JAZ1/2/5/7, PUB22 physically interacts with JAZ1/3/4/6. PUB22 ubiquitinates JAZ4 to promote its degradation via the 26S proteasome pathway. Importantly, we observed that pub22 mutants showreduced resistance to H. armigera, whereas jaz4 single mutants and jaz1 jaz3 jaz4 jaz6 quadruple mutants have enhanced resistance. The hypersensitivity of pub22 mutants to herbivores could be partially rescued by JAZ4 mutation. Moreover, we found that expression of PUB22 can be transcriptionally activated by MYC2, thus forming a positive feedback circuit in JA signaling. We noticed that the PUB22-JAZ4 module also regulates other JA responses, including defense against B. cinerea, inhibition of root elongation, and anthocyanin accumulation. Taken together, these results indicate that PUB22 plays a crucial role in plant growth and defense responses, together with COI1-regulated JA signaling, by targeting specific JAZs.

Co-overexpression of SWEET sucrose transporters modulates sucrose synthesis and defence responses to enhance immunity against bacterial blight in rice

Enhancing carbohydrate export from source to sink tissues is considered to be a realistic approach for improving photosynthetic efficiency and crop yield. The rice sucrose transporters OsSUT1, OsSWEET11a and OsSWEET14 contribute to sucrose phloem loading and seed filling. Crucially, Xanthomonas oryzae pv. oryzae (Xoo) infection in rice enhances the expression of OsSWEET11a and OsSWEET14 genes, and causes leaf blight. Here we show that co-overexpression of OsSUT1, OsSWEET11a and OsSWEET14 in rice reduced sucrose synthesis and transport leading to lower growth and yield but reduced susceptibility to Xoo relative to controls. The immunity-related hypersensitive response (HR) was enhanced in the transformed lines as indicated by the increased expression of defence genes, higher salicylic acid content and presence of HR lesions on the leaves. The results suggest that the increased expression of OsSWEET11a and OsSWEET14 in rice is perceived as a pathogen (Xoo) attack that triggers HR and results in constitutive activation of plant defences that are related to the signalling pathways of pathogen starvation. These findings provide a mechanistic basis for the trade-off between plant growth and immunity because decreased susceptibility against Xoo compromised plant growth and yield.

Superoxide signalling and antioxidant processing in the plant nucleus

The superoxide anion radical (O2•-) is a one-electron reduction product of molecular oxygen. Compared to other forms of reactive oxygen species (ROS), superoxide has limited reactivity. Nevertheless, superoxide reacts with nitic oxide, ascorbate and the iron moieties of [Fe-S] cluster-containing proteins. Superoxide has largely been neglected as a signalling molecule in the plant literature in favour of the most stable ROS form, hydrogen peroxide. However, superoxide can accumulate in plant cells, particularly in meristems, where superoxide dismutase activity and ascorbate accumulation are limited (or absent), or when superoxide is generated within the lipid environment of membranes. Moreover, oxidation of the nucleus in response to environmental stresses is a widespread phenomenon. Superoxide is generated in many intracellular including mitochondria, chloroplasts and on the apoplastic/cell wall face of the plasma membrane. However, nuclear superoxide production and functions remain poorly documented in plants. Accumulating evidence suggests that the nuclear pools of antioxidants such as glutathione are discrete and separate from the cytosolic pools, allowing compartment-specific signalling in the nucleus. We consider the potential mechanisms of superoxide generation and targets in the nucleus, together with the importance of antioxidant processing in regulating superoxide signalling.

The ascorbate/glutathione cycle coming of age

Concepts, regarding the operation of the ascorbate/glutathione cycle and the associated water/water cycle in the processing of metabolically-generated hydrogen peroxide and other forms of reactive oxygen species (ROS), are well established in the literature. However, our knowledge of functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signaling pathways that regulate plant growth, development and defense. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have "moonlighting" functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signaling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate/glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways.

Enhancing climate change resilience in agricultural crops

Climate change threatens global food and nutritional security through negative effects on crop growth and agricultural productivity. Many countries have adopted ambitious climate change mitigation and adaptation targets that will exacerbate the problem, as they require significant changes in current agri-food systems. In this review, we provide a roadmap for improved crop production that encompasses the effective transfer of current knowledge into plant breeding and crop management strategies that will underpin sustainable agriculture intensification and climate resilience. We identify the main problem areas and highlight outstanding questions and potential solutions that can be applied to mitigate the impacts of climate change on crop growth and productivity. Although translation of scientific advances into crop production lags far behind current scientific knowledge and technology, we consider that a holistic approach, combining disciplines in collaborative efforts, can drive better connections between research, policy, and the needs of society.

Prospects for developing allergen-depleted food crops

In addition to the challenge of meeting global demand for food production, there are increasing concerns about food safety and the need to protect consumer health from the negative effects of foodborne allergies. Certain bio-molecules (usually proteins) present in food can act as allergens that trigger unusual immunological reactions, with potentially life-threatening consequences. The relentless working lifestyles of the modern era often incorporate poor eating habits that include readymade prepackaged and processed foods, which contain additives such as peanuts, tree nuts, wheat, and soy-based products, rather than traditional home cooking. Of the predominant allergenic foods (soybean, wheat, fish, peanut, shellfish, tree nuts, eggs, and milk), peanuts (Arachis hypogaea) are the best characterized source of allergens, followed by tree nuts (Juglans regia, Prunus amygdalus, Corylus avellana, Carya illinoinensis, Anacardium occidentale, Pistacia vera, Bertholletia excels), wheat (Triticum aestivum), soybeans (Glycine max), and kidney beans (Phaseolus vulgaris). The prevalence of food allergies has risen significantly in recent years including chance of accidental exposure to such foods. In contrast, the standards of detection, diagnosis, and cure have not kept pace and unfortunately are often suboptimal. In this review, we mainly focus on the prevalence of allergies associated with peanut, tree nuts, wheat, soybean, and kidney bean, highlighting their physiological properties and functions as well as considering research directions for tailoring allergen gene expression. In particular, we discuss how recent advances in molecular breeding, genetic engineering, and genome editing can be used to develop potential low allergen food crops that protect consumer health.

Plant adaptation to climate change

Plants are vital to human health and well-being, as well as helping to protect the environment against the negative impacts of climate change. They are an essential part of the 'One Health' strategy that seeks to balance and optimize the health of people, animals and the environment. Crucially, plants are central to nature-based solutions to climate mitigation, not least because soil carbon storage is an attractive strategy for mitigating greenhouse gas emissions and the associated climate change. Agriculture depends on genetically pure, high-quality seeds that are free from pests and pathogens and contain a required degree of genetic purity. This themed collection addresses key questions in the field encompassing the biochemical mechanisms that underlie plant responses and adaptations to a changing climate. This collection encompasses an analysis of the biochemistry and molecular mechanisms underpinning crop and forest resilience, together with considerations of plant adaptations to climate change-associated stresses, including drought, floods and heatwaves, and the increased threats posed by pathogens and pests.

Restraining Quiescence Release-Related Ageing in Plant Cells: A Case Study in Carrot

The blackening of cut carrots causes substantial economic losses to the food industry. Blackening was not observed in carrots that had been stored underground for less than a year, but the susceptibility to blackening increased with the age of the carrots that were stored underground for longer periods. Samples of black, border, and orange tissues from processed carrot batons and slices, prepared under industry standard conditions, were analyzed to identify the molecular and metabolic mechanisms underpinning processing-induced blackening. The black tissues showed substantial molecular and metabolic rewiring and large changes in the cell wall structure, with a decreased abundance of xyloglucan, pectins (homogalacturonan, rhamnogalacturonan-I, galactan and arabinan), and higher levels of lignin and other phenolic compounds when compared to orange tissues. Metabolite profiling analysis showed that there was a major shift from primary to secondary metabolism in the black tissues, which were depleted in sugars, amino acids, and tricarboxylic acid (TCA) cycle intermediates but were rich in phenolic compounds. These findings suggest that processing triggers a release from quiescence. Transcripts encoding proteins associated with secondary metabolism were less abundant in the black tissues, but there were no increases in transcripts associated with oxidative stress responses, programmed cell death, or senescence. We conclude that restraining quiescence release alters cell wall metabolism and composition, particularly regarding pectin composition, in a manner that increases susceptibility to blackening upon processing.

The impact of GmTSA and GmALS on soybean salt tolerance: uncovering the molecular landscape of amino acid and secondary metabolism pathways

KEY MESSAGE

GmTSA and GmALS were screened out for salt stress in soybean and explore the poteintial amino acid secondary metabolism pathways. Soybean (Glycine max L.) is an oil and protein crop of global importance, and salinity has significant effects on soybean growth. Here, a population of soybean chromosome segment substitution lines was screened to identify highly salt-tolerant lines. In total, 24 quantitative trait loci (QTLs) on seven chromosomes were associated with salt tolerance, and CSSL_R71 was selected for further analysis. Although numerous genes were differentially expressed in CSSL_R71 in response to salt statically no differently, transcript levels of classical salt-response genes, including those of the salt overly sensitive pathway. Rather, salt tolerance in CSSL_R71 was associated with changes in amino acid and lipid metabolism. In particular, changes in p-coumaric acid, shikimic acid, and pyrrole-2-carboxylic acid levels accompanied salt tolerance in CSSL_R71. Eleven differentially expressed genes (DEGs) related to amino acid and secondary metabolism were identified as candidate genes on the substituted chromosome fragment. Six of these showed differences in coding sequence between the parental genotypes. Crucially, overexpression of GmTSA (Glyma.03G158400, tryptophan synthase) significantly enhanced salt tolerance in soybean hairy roots, whereas overexpression of GmALS (Glyma.13G241000, acetolactate synthase) decreased salt tolerance. Two KASP markers were developed for GmALS and used to genotype salt-tolerant and salt-sensitive lines in the CSSL population. Non-synonymous mutations were directly associated with salt tolerance. Taken together, these data provide evidence that changes in amino acid and secondary metabolism have the potential to confer salt tolerance in soybean.

WHIRLY proteins maintain seed longevity by effects on seed oxygen signalling during imbibition

The WHIRLY (WHY) family of DNA/RNA binding proteins fulfil multiple but poorly characterised functions in plants. We analysed WHY protein functions in the Arabidopsis Atwhy1, Atwhy3, Atwhy1why3 single and double mutants and wild type controls. The Atwhy3 and Atwhy1why3 double mutants showed a significant delay in flowering, having more siliques per plant but with fewer seeds per silique than the wild type. While germination was similar in the unaged high-quality seeds of all lines, significant decreases in vigour and viability were observed in the aged mutant seeds compared with the wild type. Imbibition of unaged high-quality seeds was characterised by large increases in transcripts that encode proteins involved in oxygen sensing and responses to hypoxia. Seed aging resulted in a disruption of the imbibition-induced transcriptome profile such that transcripts encoding RNA metabolism and processing became the most abundant components of the imbibition signature. The imbibition-related profile of the Atwhy1why3 mutant seeds, was characterised by decreased expression of hypoxia-related and oxygen metabolism genes even in the absence of aging. Seed aging further decreased the abundance of hypoxia-related and oxygen metabolism transcripts relative to the wild type. These findings suggest that the WHY1 and WHY3 proteins regulate the imbibition-induced responses to oxygen availability and hypoxia. Loss of WHY1 and WHY3 functions decreases the ability of Arabidopsis seeds to resist the adverse effects of seed aging.

Hydrogen Cyanamide Causes Reversible G2/M Cell Cycle Arrest Accompanied by Oxidation of the Nucleus and Cytosol

Hydrogen cyanamide (HC) has been widely used in horticulture to trigger bud burst following dormancy. Its use has been banned in some countries due to human health concerns, however the search for effective safe alternatives is delayed by lack of knowledge of the mechanism of HC action. Earlier studies demonstrate that HC stimulates the production of reactive oxygen species (ROS) and alters the rate of cell division. However, the relationships between HC effects on ROS, redox (reduction/oxidation) homeostasis and cell division are unknown. This study used Arabidopsis thaliana ((L.) Heynh.) seedlings expressing the redox reporter roGFP2 to measure the oxidation states of the nuclei and cytosol in response to HC treatment. The Cytrap dual cell cycle phase marker system and flow cytometry were used to study associated changes in cell proliferation. HC (1.5 mM) reversibly inhibited root growth during a 24 h treatment. Higher concentrations were not reversible. HC did not synchronise the cell cycle, in contrast to hydroxyurea. Rather, HC caused a gradual accumulation of cells in the G2/M phase and decline of G1/S phase cells, 16 to 24 h post-treatment. This was accompanied by increased oxidation of both the nuclei and cytosol. Taken together, these findings show that HC impairs proliferation of embryonic root meristem cells in a reversible manner through restriction of G2/M transition accompanied by increased cellular oxidation.

Metabolic regulation of quiescence in plants

Quiescence is a crucial survival attribute in which cell division is repressed in a reversible manner. Although quiescence has long been viewed as an inactive state, recent studies have shown that it is an actively monitored process that is influenced by environmental stimuli. Here, we provide a perspective of the quiescent state and discuss how this process is tuned by energy, nutrient and oxygen status, and the pathways that sense and transmit these signals. We not only highlight the governance of canonical regulators and signalling mechanisms that respond to changes in nutrient and energy status, but also consider the central significance of mitochondrial functions and cues as key regulators of nuclear gene expression. Furthermore, we discuss how reactive oxygen species and the associated redox processes, which are intrinsically linked to energy carbohydrate metabolism, also play a key role in the orchestration of quiescence.

The integration of reactive oxygen species (ROS) and calcium signalling in abiotic stress responses

Reactive oxygen species (ROS) and calcium (Ca²⁺ ) signalling are interconnected in the perception and transmission of environmental signals that control plant growth, development and defence. The concept that systemically propagating Ca²⁺ and ROS waves function together with electric signals in directional cell-to-cell systemic signalling and even plant-to-plant communication, is now firmly imbedded in the literature. However, relatively few mechanistic details are available regarding the management of ROS and Ca²⁺ signals at the molecular level, or how synchronous and independent signalling might be achieved in different cellular compartments. This review discusses the proteins that may serve as nodes or connecting bridges between the different pathways during abiotic stress responses, highlighting the crosstalk between ROS and Ca²⁺ pathways in cell signalling. We consider putative molecular switches that connect these signalling pathways and the molecular machinery that achieves the synergistic operation of ROS and Ca²⁺ signals.

Agrifood and net zero

We consider the science, policy, and implementation (science-policy-society interface) issues around the agrifood system and the UK's transition to net zero. We conclude that agrifood policy should become more targeted, and the marriage of top-down and bottom-up approaches is key to co-create a pathway that is plausible for each stakeholder.

HY5 functions as a systemic signal by integrating BRC1-dependent hormone signaling in tomato bud outgrowth

Light plays an important role in determining plant architecture, which greatly influences crop yield. However, the precise mechanisms by which light signaling regulates bud outgrowth remain to be identified. Here, we show that light regulates bud outgrowth via both HY5 and brassinosteroid (BR)-dependent pathways in tomato. Inactivation of the red-light photoreceptor PHYB, or deficiencies in PHYB or the blue-light photoreceptor CRY1a, inhibits bud outgrowth and leads to decreased accumulation of HY5 protein and increased transcript level of BRANCHED1 (BRC1), a central integrator of branching signals. HY5, functioning as a mobile systemic signal from leaves, promotes bud outgrowth by directly suppressing BRC1 transcript and activating the transcript of BR biosynthesis genes within the lateral buds in tomato. Furthermore, BRC1 prevents the accumulation of cytokinin (CK) and gibberellin (GA) by directly inhibiting the transcript of CK synthesis gene LOG4, while increasing the transcript levels of CK and GA degradation genes (CKX7, GA2ox4, and GA2ox5), leading to an arrest of bud outgrowth. Moreover, bud outgrowth occurs predominantly in the day due to the suppression of BRC1 transcript by HY5. These findings demonstrate that light-inducible HY5 acts as a systemic signaling factor in fine-tuning the bud outgrowth of tomato.

Catalase: A critical node in the regulation of cell fate

Catalase (CAT) is an extensively studied if somewhat enigmatic enzyme that is at the heart of eukaryotic antioxidant systems with a canonical role in peroxisomal function. The CAT family of proteins exert control over a wide range of plant growth and defence processes. CAT proteins are subject to many types of post-translational modification (PTM), which modify activity, ligand binding, stability, compartmentation and function. The CAT interactome involves many cytosolic and nuclear proteins that appear to be essential for protein functions. Hence, the CAT network of roles extends far beyond those associated with peroxisomal metabolism. Some pathogen effector proteins are able to redirect CAT to the nucleus and recent evidence indicates CAT can traffic to the nucleus in the absence of exogenous proteins. While the mechanisms that target CAT to the nucleus are not understood, CAT activity in the cytosol and nucleus is promoted by interactions with nucleoredoxin. Here we discuss recent findings that have been pivotal in generating a step change in our understanding of CAT functions in plant cells.

Phytosulfokine peptide optimizes plant growth and defense via glutamine synthetase GS2 phosphorylation in tomato

Phytosulfokine (PSK) is a plant pentapeptide hormone that fulfills a wide range of functions. Although PSK has frequently been reported to function in the inverse regulation of growth and defense in response to (hemi)biotrophic pathogens, the mechanisms involved remain largely unknown. Using the tomato (Solanum lycopersicum) and Pseudomonas syringae pv. tomato (Pst) DC3000 pathogen system, we present compelling evidence that the PSK receptor PSKR1 interacts with the calcium-dependent protein kinase CPK28, which in turn phosphorylates the key enzyme of nitrogen assimilation glutamine synthetase GS2 at two sites (Serine-334 and Serine-360). GS2 phosphorylation at S334 specifically regulates plant defense, whereas S360 regulates growth, uncoupling the PSK-induced effects on defense responses and growth regulation. The discovery of these sites will inform breeding strategies designed to optimize the growth-defense balance in a compatible manner.

WHIRLY protein functions in plants

Environmental stresses pose a significant threat to food security. Understanding the function of proteins that regulate plant responses to biotic and abiotic stresses is therefore pivotal in developing strategies for crop improvement. The WHIRLY (WHY) family of DNA-binding proteins are important in this regard because they fulfil a portfolio of important functions in organelles and nuclei. The WHY1 and WHY2 proteins function as transcription factors in the nucleus regulating phytohormone synthesis and associated growth and stress responses, as well as fulfilling crucial roles in DNA and RNA metabolism in plastids and mitochondria. WHY1, WHY2 (and WHY3 proteins in Arabidopsis) maintain organelle genome stability and serve as auxiliary factors for homologous recombination and double-strand break repair. Our understanding of WHY protein functions has greatly increased in recent years, as has our knowledge of the flexibility of their localization and overlap of functions but there is no review of the topic in the literature. Our aim in this review was therefore to provide a comprehensive overview of the topic, discussing WHY protein functions in nuclei and organelles and highlighting roles in plant development and stress responses. In particular, we consider areas of uncertainty such as the flexible localization of WHY proteins in terms of retrograde signalling connecting mitochondria, plastids, and the nucleus. Moreover, we identify WHY proteins as important targets in plant breeding programmes designed to increase stress tolerance and the sustainability of crop yield in a changing climate.

Biofortification of common bean (Phaseolus vulgaris L.) with iron and zinc: Achievements and challenges

Micronutrient deficiencies (hidden hunger), particularly in iron (Fe) and zinc (Zn), remain one of the most serious public health challenges, affecting more than three billion people globally. A number of strategies are used to ameliorate the problem of micronutrient deficiencies and to improve the nutritional profile of food products. These include (i) dietary diversification, (ii) industrial food fortification and supplements, (iii) agronomic approaches including soil mineral fertilisation, bioinoculants and crop rotations, and (iv) biofortification through the implementation of biotechnology including gene editing and plant breeding. These efforts must consider the dietary patterns and culinary preferences of the consumer and stakeholder acceptance of new biofortified varieties. Deficiencies in Zn and Fe are often linked to the poor nutritional status of agricultural soils, resulting in low amounts and/or poor availability of these nutrients in staple food crops such as common bean. This review describes the genes and processes associated with Fe and Zn accumulation in common bean, a significant food source in Africa that plays an important role in nutritional security. We discuss the conventional plant breeding, transgenic and gene editing approaches that are being deployed to improve Fe and Zn accumulation in beans. We also consider the requirements of successful bean biofortification programmes, highlighting gaps in current knowledge, possible solutions and future perspectives.

Physiological implications of SWEETs in plants and their potential applications in improving source-sink relationships for enhanced yield

The sugars will eventually be exported transporters (SWEET) family of transporters in plants is identified as a novel class of sugar carriers capable of transporting sugars, sugar alcohols and hormones. Functioning in intercellular sugar transport, SWEETs influence a wide range of physiologically important processes. SWEETs regulate the development of sink organs by providing nutritional support from source leaves, responses to abiotic stresses by maintaining intracellular sugar concentrations, and host-pathogen interactions through the modulation of apoplastic sugar levels. Many bacterial and fungal pathogens activate the expression of SWEET genes in species such as rice and Arabidopsis to gain access to the nutrients that support virulence. The genetic manipulation of SWEETs has led to the generation of bacterial blight (BB)-resistant rice varieties. Similarly, while the overexpression of the SWEETs involved in sucrose export from leaves and pathogenesis led to growth retardation and yield penalties, plants overexpressing SWEETs show improved disease resistance. Such findings demonstrate the complex functions of SWEETs in growth and stress tolerance. Here, we review the importance of SWEETs in plant-pathogen and source-sink interactions and abiotic stress resistance. We highlight the possible applications of SWEETs in crop improvement programmes aimed at improving sink and source strengths important for enhancing the sustainability of yield. We discuss how the adverse effects of the overexpression of SWEETs on plant growth may be overcome.

Herbivore-induced Ca2+ signals trigger a jasmonate burst by activating ERF16-mediated expression in tomato

Herbivory severely affects plant growth, posing a threat to crop production. Calcium ion (Ca²⁺ ) signaling and accumulation of jasmonates (JAs) are activated in plant response to herbivore attack, leading to the expression of defense pathways. However, little is known about how the Ca²⁺ signal modulates JA biosynthesis. We used diverse techniques, including CRISPR/Cas9, UPLC-MS/MS and molecular biology methods to explore the role of ETHYLENE RESPONSE FACTOR 16 in Ca²⁺ signal-triggered JA burst during herbivore defense in tomato. Here we show that simulated herbivory induces GLUTAMATE RECEPTOR LIKE3.3/3.5 (GLR3.3/3.5)-dependent increases in electrical activity, Ca²⁺ influx and increases the abundance of CALMODULIN2 (CaM2) and ERF16 transcripts in tomato. The interaction between CaM2 and ERF16 promotes JA biosynthesis by enhancing the transcriptional activity of ERF16, which increases the activation of ERF16 expression and causes expression of LIPOXYGENASE D (LOXD), AOC and 12-OXO-PHYTODIENOIC ACID REDUCTASE 3 (OPR3), the key genes in JA biosynthesis. Mutation of CaM2 results in decreased JA accumulation, together with the expression of JA biosynthesis-related genes, leading to reduced resistance to the cotton bollworm Helicoverpa armigera. These findings reveal a molecular mechanism underpinning the Ca²⁺ signal-initiated systemic JA burst and emphasize the pivotal role of Ca²⁺ signal/ERF16 crosstalk in herbivore defense.

Non-volatile signals and redox mechanisms are required for the responses of Arabidopsis roots to Pseudomonas oryzihabitans

Soil bacteria promote plant growth and protect against environmental stresses, but the mechanisms involved remain poorly characterized, particularly when there is no direct contact between the roots and bacteria. Here, we explored the effects of Pseudomonas oryzihabitans PGP01 on the root system architecture (RSA) in Arabidopsis thaliana seedlings. Significant increases in lateral root (LR) density were observed when seedlings were grown in the presence of P. oryzihabitans, as well as an increased abundance of transcripts associated with altered nutrient transport and phytohormone responses. However, no bacterial transcripts were detected on the root samples by RNAseq analysis, demonstrating that the bacteria do not colonize the roots. Separating the agar containing bacteria from the seedlings prevented the bacteria-induced changes in RSA. Bacteria-induced changes in RSA were absent from mutants defective in ethylene response factor (ERF109), glutathione synthesis (pad2-1, cad2-1, and rax1-1) and in strigolactone synthesis (max3-9 and max4-1) or signalling (max2-3). However, the P. oryzihabitans-induced changes in RSA were similar in the low ascorbate mutants (vtc2-1and vtc2-2) to the wild-type controls. Taken together, these results demonstrate the importance of non-volatile signals and redox mechanisms in the root architecture regulation that occurs following long-distance perception of P. oryzihabitans.

The Effects of High CO2 and Strigolactones on Shoot Branching and Aphid-Plant Compatibility Control in Pea

Elevated atmospheric CO2 concentrations (eCO2) regulate plant architecture and susceptibility to insects. We explored the mechanisms underpinning these responses in wild type (WT) peas and mutants defective in either strigolactone (SL) synthesis or signaling. All genotypes had increased shoot height and branching, dry weights and carbohydrate levels under eCO2, demonstrating that SLs are not required for shoot acclimation to eCO2. Since shoot levels of jasmonic acid (JA) and salicylic acid (SA) tended to be lower in SL signaling mutants than the WT under ambient conditions, we compared pea aphid performance on these lines under both CO2 conditions. Aphid fecundity was increased in the SL mutants compared to the WT under both ambient and eCO2 conditions. Aphid infestation significantly decreased levels of JA, isopentenyladenine, trans-zeatin and gibberellin A4 and increased ethylene precursor ACC, gibberellin A1, gibberellic acid (GA3) and SA accumulation in all lines. However, GA3 levels were increased less in the SL signaling mutants than the WT. These studies provide new insights into phytohormone responses in this specific aphid/host interaction and suggest that SLs and gibberellins are part of the network of phytohormones that participate in host susceptibility.

Glucose sensing by regulator of G protein signaling 1 (RGS1) plays a crucial role in coordinating defense in response to environmental variation in tomato

Low light intensities affect the outbreak of plant diseases. However, the underlying molecular mechanisms remain poorly understood. High-performance liquid chromatography analysis of tomato (Solanum lycopersicum) revealed that apoplastic glucose (Glc) levels decreased in response to low light. Conversely, low-light-induced susceptibility to Pseudomonas syringae pv tomato (Pst) DC3000 was significantly alleviated by exogenous Glc treatment. Using cell-based biolayer interferometry assays, we found that Glc specifically binds to the tomato regulator of G protein signaling 1 (RGS1). Laser scanning confocal microscopy imaging revealed that Glc triggers RGS1 endocytosis, which influences the uncoupling of the RGS1-Gα (GPA1) and GPA1-Gβ (SlGB1) proteins, in a dose- and duration-dependent manner. Analysis of G protein single and double mutants revealed that RGS1 negatively regulates disease resistance under low light and is required for Glc-enhanced defense. Downstream of RGS1-Glc binding, GPA1 negatively mediates the light-intensity-regulated defense, whereas SlGB1 positively regulates this process. These results reveal a novel light-intensity-responsive defense system that is mediated by a Glc-RGS1-G protein signaling pathway. This information will be critical for future investigations of how plant cells sense extracellular sugars and adjust defense under different environments, as well as for genetic engineering approaches to improve stress resilience.

ROS production and signalling in chloroplasts: cornerstones and evolving concepts

Reactive oxygen species (ROS) such as singlet oxygen, superoxide (O₂^●- ) and hydrogen peroxide (H₂ O₂ ) are the markers of living cells. Oxygenic photosynthesis produces ROS in abundance, which act as a readout of a functional electron transport system and metabolism. The concept that photosynthetic ROS production is a major driving force in chloroplast to nucleus retrograde signalling is embedded in the literature, as is the role of chloroplasts as environmental sensors. The different complexes and components of the photosynthetic electron transport chain (PETC) regulate O₂^●- production in relation to light energy availability and the redox state of the stromal Cys-based redox systems. All of the ROS generated in chloroplasts have the potential to act as signals and there are many sulphhydryl-containing proteins and peptides in chloroplasts that have the potential to act as H₂ O₂ sensors and function in signal transduction. While ROS may directly move out of the chloroplasts to other cellular compartments, ROS signalling pathways can only be triggered if appropriate ROS-sensing proteins are present at or near the site of ROS production. Chloroplast antioxidant systems serve either to propagate these signals or to remove excess ROS that cannot effectively be harnessed in signalling. The key challenge is to understand how regulated ROS delivery from the PETC to the Cys-based redox machinery is organised to transmit redox signals from the environment to the nucleus. Redox changes associated with stromal carbohydrate metabolism also play a key role in chloroplast signalling pathways.

The bud dormancy disconnect: latent buds of grapevine are dormant during summer despite a high metabolic rate

Grapevine (Vitis vinifera L.) displays wide plasticity to climate; however, the physiology of dormancy along a seasonal continuum is poorly understood. Here we investigated the apparent disconnect between dormancy and the underlying respiratory physiology and transcriptome of grapevine buds, from bud set in summer to bud burst in spring. The establishment of dormancy in summer was pronounced and reproducible; however, this was coupled with little or no change in physiology, indicated by respiration, hydration, and tissue oxygen tension. The release of dormancy was biphasic; the depth of dormancy declined substantially by mid-autumn, while the subsequent decline towards spring was moderate. Observed changes in physiology failed to explain the first phase of dormancy decline, in particular. Transcriptome data contrasting development from summer through to spring also indicated that dormancy was poorly reflected by metabolic quiescence during summer and autumn. Gene Ontology and enrichment data revealed the prevailing influence of abscisic acid (ABA)-related gene expression during the transition from summer to autumn, and promoter motif analysis suggested that photoperiod may play an important role in regulating ABA functions during the establishment of dormancy. Transcriptomic data from later transitions reinforced the importance of oxidation and hypoxia as physiological cues to regulate the maintenance of quiescence and resumption of growth. Collectively these data reveal a novel disconnect between growth and metabolic quiescence in grapevine following bud set, which requires further experimentation to explain the phenology and dormancy relationships.

Nuclear and peroxisomal targeting of catalase

Catalase is a well-known component of the cellular antioxidant network, but there have been conflicting conclusions reached regarding the nature of its peroxisome targeting signal. It has also been reported that catalase can be hijacked to the nucleus by effector proteins of plant pathogens. Using a physiologically relevant system where native untagged catalase variants are expressed in a cat2-1 mutant background, the C terminal most 18 amino acids could be deleted without affecting activity, peroxisomal targeting or ability to complement multiple phenotypes of the cat2-1 mutant. In contrast, converting the native C terminal tripeptide PSI to the canonical PTS1 sequence ARL resulted in lower catalase specific activity. Localisation experiments using split superfolder green fluorescent protein revealed that catalase can be targeted to the nucleus in the absence of any pathogen effectors, and that C terminal tagging in combination with alterations of the native C terminus can interfere with nuclear localisation. These findings provide fundamental new insights into catalase targeting and pave the way for exploration of the mechanism of catalase targeting to the nucleus and its role in non-infected plants.

Late Embryogenesis Abundant (LEA)5 Regulates Translation in Mitochondria and Chloroplasts to Enhance Growth and Stress Tolerance

The late embryogenesis abundant (LEA)5 protein is predominantly expressed in Arabidopsis leaves in the dark, the levels of LEA5 transcripts decreasing rapidly upon illumination. LEA5 is important in plant responses to environmental stresses but the mechanisms involved have not been elucidated. We therefore explored LEA5 functions in Arabidopsis mutants (lea5) and transgenic Arabidopsis plants constitutively expressing LEA5 (OEX 2-5), as well as in transgenic barley lines expressing the Arabidopsis LEA5 gene. The OEX 2-5 plants grew better than controls and lea5 mutants in the presence of the prooxidants methyl viologen and menadione. Confocal microscopy of Arabidopsis mesophyll protoplasts expressing a LEA5-YFP fusion protein demonstrated that LEA5 could be localized to chloroplasts as well as mitochondria in Arabidopsis protoplasts. Tandem affinity purification (TAP) analysis revealed LEA5 interacts with the chloroplast DEAD-box ATP-dependent RNA helicase 22 (RH22) in Arabidopsis cells. Split YFP analysis confirmed the interaction between RH22 and LEA5 in chloroplasts. The abundance of translated protein products in chloroplasts was decreased in transgenic Arabidopsis plants and increased in lea5 knockout mutants. Conversely, the abundance of translated mitochondrial protein products was increased in OEX 2-5 plants and decreased in lea5 mutants. Mitochondrial electron transport rates were higher in the OEX 2-5 plants than the wild type. The transformed barley lines expressing the Arabidopsis LEA5 had increased seed yields, but they showed a greater drought-induced inhibition of photosynthesis than controls. Taken together, these data demonstrate that LEA5 regulates organellar translation, in order to enhance respiration relative to photosynthesis in response to stress.

Stress effects on the reactive oxygen species-dependent regulation of plant growth and development

Plant growth is mediated by cell proliferation and expansion. Both processes are controlled by a network of endogenous factors such as phytohormones, reactive oxygen species (ROS), sugars, and other signals, which influence gene expression and post-translational regulation of proteins. Stress resilience requires rapid and appropriate responses in plant growth and development as well as defence. Regulation of ROS accumulation in different cellular compartments influences growth responses to abiotic and biotic stresses. While ROS are essential for growth, they are also implicated in the stress-induced cessation of growth and, in some cases, programmed cell death. It is widely accepted that redox post-translational modifications of key proteins determine the growth changes and cell fate responses to stress, but the molecular pathways and factors involved remain poorly characterized. Here we discuss ROS as a signalling molecule, the mechanisms of ROS-dependent regulation that influence protein-protein interactions, protein function, and turnover, together with the relocation of key proteins to different intracellular compartments in a manner that can alter cell fate. Understanding how the redox interactome responds to stress-induced increases in ROS may provide a road map to tailoring the dynamic ROS interactions that determine growth and cell fate in order to enhance stress resilience.

Photosynthetic quantum efficiency in south-eastern Amazonian trees may be already affected by climate change

Tropical forests are experiencing unprecedented high-temperature conditions due to climate change that could limit their photosynthetic functions. We studied the high-temperature sensitivity of photosynthesis in a rainforest site in southern Amazonia, where some of the highest temperatures and most rapid warming in the Tropics have been recorded. The quantum yield (F_v /F_m ) of photosystem II was measured in seven dominant tree species using leaf discs exposed to varying levels of heat stress. T₅₀ was calculated as the temperature at which F_v /F_m was half the maximum value. T₅ is defined as the breakpoint temperature, at which F_v /F_m decline was initiated. Leaf thermotolerance in the rapidly warming southern Amazonia was the highest recorded for forest tree species globally. T₅₀ and T₅ varied between species, with one mid-storey species, Amaioua guianensis, exhibiting particularly high T₅₀ and T₅ values. While the T₅₀ values of the species sampled were several degrees above the maximum air temperatures experienced in southern Amazonia, the T₅ values of several species are now exceeded under present-day maximum air temperatures.

The protein kinase CPK28 phosphorylates ascorbate peroxidase and enhances thermotolerance in tomato

High temperatures are a major threat to plant growth and development, leading to yield losses in crops. Calcium-dependent protein kinases (CPKs) act as critical components of Ca2+ sensing in plants that transduce rapid stress-induced responses to multiple environmental stimuli. However, the role of CPKs in plant thermotolerance and their mechanisms of action remain poorly understood. To address this issue, tomato (Solanum lycopersicum) cpk28 mutants were generated using a CRISPR-Cas9 gene-editing approach. The responses of mutant and wild-type plants to normal (25°C) and high temperatures (45°C) were documented. Thermotolerance was significantly decreased in the cpk28 mutants, which showed increased heat stress-induced accumulation of reactive oxygen species (ROS) and levels of protein oxidation, together with decreased activities of ascorbate peroxidase (APX) and other antioxidant enzymes. The redox status of ascorbate and glutathione were also modified. Using a yeast two-hybrid library screen and protein interaction assays, we provide evidence that CPK28 directly interacts with cytosolic APX2. Mutations in APX2 rendered plants more sensitive to high temperatures, whereas the addition of exogenous reduced ascorbate (AsA) rescued the thermotolerance phenotype of the cpk28 mutants. Moreover, protein phosphorylation analysis demonstrated that CPK28 phosphorylates the APX2 protein at Thr-59 and Thr-164. This process is suggested to be responsive to Ca2+ stimuli and may be required for CPK28-mediated thermotolerance. Taken together, these results demonstrate that CPK28 targets APX2, thus improving thermotolerance. This study suggests that CPK28 is an attractive target for the development of improved crop cultivars that are better adapted to heat stress in a changing climate.

Gaining Acceptance of Novel Plant Breeding Technologies

Ensuring the sustainability of agriculture under climate change has led to a surge in alternative strategies for crop improvement. Advances in integrated crop breeding, social acceptance, and farm-level adoption are crucial to address future challenges to food security. Societal acceptance can be slow when consumers do not see the need for innovation or immediate benefits. We consider how best to address the issue of social licence and harmonised governance for novel gene technologies in plant breeding. In addition, we highlight optimised breeding strategies that will enable long-term genetic gains to be achieved. Promoted by harmonised global policy change, innovative plant breeding can realise high and sustainable productivity together with enhanced nutritional traits.

Oxygen and reactive oxygen species-dependent regulation of plant growth and development

Oxygen and reactive oxygen species (ROS) have been co-opted during evolution into the regulation of plant growth, development, and differentiation. ROS and oxidative signals arising from metabolism or phytohormone-mediated processes control almost every aspect of plant development from seed and bud dormancy, liberation of meristematic cells from the quiescent state, root and shoot growth, and architecture, to flowering and seed production. Moreover, the phytochrome and phytohormone-dependent transmissions of ROS waves are central to the systemic whole plant signaling pathways that integrate root and shoot growth. The sensing of oxygen availability through the PROTEOLYSIS 6 (PRT6) N-degron pathway functions alongside ROS production and signaling but how these pathways interact in developing organs remains poorly understood. Considerable progress has been made in our understanding of the nature of hydrogen peroxide sensors and the role of thiol-dependent signaling networks in the transmission of ROS signals. Reduction/oxidation (redox) changes in the glutathione (GSH) pool, glutaredoxins (GRXs), and thioredoxins (TRXs) are important in the control of growth mediated by phytohormone pathways. Although, it is clear that the redox states of proteins involved in plant growth and development are controlled by the NAD(P)H thioredoxin reductase (NTR)/TRX and reduced GSH/GRX systems of the cytosol, chloroplasts, mitochondria, and nucleus, we have only scratched the surface of this multilayered control and how redox-regulated processes interact with other cell signaling systems.

The phyB-dependent induction of HY5 promotes iron uptake by systemically activating FER expression

Iron (Fe) deficiency affects global crop productivity and human health. However, the role of light signaling in plant Fe uptake remains uncharacterized. Here, we find that light-induced Fe uptake in tomato (Solanum lycopersicum L.) is largely dependent on phytochrome B (phyB). Light induces the phyB-dependent accumulation of ELONGATED HYPOCOTYL 5 (HY5) protein both in the leaves and roots. HY5 movement from shoots to roots activates the expression of FER transcription factor, leading to the accumulation of transcripts involved in Fe uptake. Mutation in FER abolishes the light quality-induced changes in Fe uptake. The low Fe uptake observed in phyB, hy5, and fer mutants is accompanied by lower photosynthetic electron transport rates. Exposure to red light at night increases Fe accumulation in wild-type fruit but has little effects on fruit of phyB mutants. Taken together, these results demonstrate that Fe uptake is systemically regulated by light in a phyB-HY5-FER-dependent manner. These findings provide new insights how the manipulation of light quality could be used to improve Fe uptake and hence the nutritional quality of crops.

Papain-like cysteine proteases are required for the regulation of photosynthetic gene expression and acclimation to high light stress

Chloroplasts are considered to be devoid of cysteine proteases. Using transgenic Arabidopsis lines expressing the rice cystatin, oryzacystatin I (OC-I), in the chloroplasts (PC lines) or cytosol (CYS lines), we explored the hypothesis that cysteine proteases regulate photosynthesis. The CYS and PC lines flowered later than the wild type (WT) and accumulated more biomass after flowering. In contrast to the PC rosettes, which accumulated more leaf chlorophyll and carotenoid pigments than the WT, the CYS lines had lower amounts of leaf pigments. High-light-dependent decreases in photosynthetic carbon assimilation and the abundance of the Rubisco large subunit protein, the D1 protein, and the phosphorylated form of D1 proteins were attenuated in the CYS lines and reversed in the PC lines relative to the WT. However, the transgenic lines had higher amounts of LHC, rbcs, pasbA, and pasbD transcripts than the WT, and also showed modified chloroplast to nucleus signalling. We conclude that cysteine proteases accelerate the reconfiguration of the chloroplast proteome after flowering and in response to high-light stress. Inhibition of cysteine proteases, such as AtCEP1, slows chloroplast protein degradation and stimulates photosynthetic gene expression and chloroplast to nucleus signalling, enhancing stress tolerance traits.

Ethylene response factors 15 and 16 trigger jasmonate biosynthesis in tomato during herbivore resistance

Jasmonates (JAs) are phytohormones with crucial roles in plant defense. Plants accumulate JAs in response to wounding or herbivore attack, but how JA biosynthesis is triggered remains poorly understood. Here we show that herbivory by cotton bollworm (Helicoverpa armigera) induced both ethylene (ET) and JA production in tomato (Solanum lycopersicum) leaves. Using RNA-seq, ET mutants, and inhibitors of ET signaling, we identified ET-induced ETHYLENE RESPONSE FACTOR 15 (ERF15) and ERF16 as critical regulators of JA biosynthesis in tomato plants. Transcripts of ERF15 and ERF16 were markedly upregulated and peaked at 60 and 15 min, respectively, after simulated herbivore attack. While mutation in ERF16 resulted in the attenuated expression of JA biosynthetic genes and decreased JA accumulation 15 min after the simulated herbivory treatment, these changes were not observed in erf15 mutants until 60 min after treatment. Electrophoretic mobility shift assays and dual-luciferase assays demonstrated that both ERFs15 and 16 are transcriptional activators of LIPOXYGENASE D, ALLENE OXIDE CYCLASE, and 12-OXO-PHYTODIENOIC ACID REDUCTASE 3, key genes in JA biosynthesis. Furthermore, JA-activated MYC2 and ERF16 also function as the transcriptional activators of ERF16, contributing to dramatic increases in ERF16 expression. Taken together, our results demonstrated that ET signaling is involved in the rapid induction of the JA burst. ET-induced ERF15 and ERF16 function as powerful transcriptional activators that trigger the JA burst in response to herbivore attack.

High CO2 - and pathogen-driven expression of the carbonic anhydrase βCA3 confers basal immunity in tomato

Atmospheric CO₂ concentrations exert a strong influence on the susceptibility of plants to pathogens. However, the mechanisms involved in the CO₂ -dependent regulation of pathogen resistance are largely unknown. Here we show that the expression of tomato (Solanum lycopersicum) β-CARBONIC ANHYDRASE 3 (βCA3) is induced by the virulent pathogen Pseudomonas syringae pv. tomato DC3000. The role of βCA3 in the high CO₂ -mediated response in tomato and two other Solanaceae crops is distinct from that in Arabidopsis thaliana. Using βCA3 knock-out and over-expression plants, we demonstrate that βCA3 plays a positive role in the activation of basal immunity, particularly under high CO₂ . βCA3 is transcriptionally activated by the transcription factor NAC43 and is also post-translationally regulated by the receptor-like kinase GRACE1. The βCA3 pathway of basal immunity is independent on stomatal- and salicylic-acid-dependent regulation. Global transcriptome analysis and cell wall metabolite measurement implicate cell wall metabolism/integrity in βCA3-mediated basal immunity under both CO₂ conditions. These data not only highlight the importance of βCA3 in plant basal immunity under high CO₂ in a well-studied susceptible crop-pathogen system, but they also point to new targets for disease management strategies in a changing climate.

Heat-Induced Oxidation of the Nuclei and Cytosol

The concept that heat stress (HS) causes a large accumulation of reactive oxygen species (ROS) is widely accepted. However, the intracellular compartmentation of ROS accumulation has been poorly characterized. We therefore used redox-sensitive green fluorescent protein (roGFP2) to provide compartment-specific information on heat-induced redox changes of the nuclei and cytosol of Arabidopsis leaf epidermal and stomatal guard cells. We show that HS causes a large increase in the degree of oxidation of both compartments, causing large shifts in the glutathione redox potentials of the cells. Heat-induced increases in the levels of the marker transcripts, heat shock protein (HSP)101, and ascorbate peroxidase (APX)2 were maximal after 15 min of the onset of the heat treatment. RNAseq analysis of the transcript profiles of the control and heat-treated seedlings revealed large changes in transcripts encoding HSPs, mitochondrial proteins, transcription factors, and other nuclear localized components. We conclude that HS causes extensive oxidation of the nucleus as well as the cytosol. We propose that the heat-induced changes in the nuclear redox state are central to both genetic and epigenetic control of plant responses to HS.

New insights into Arabidopsis transcriptome complexity revealed by direct sequencing of native RNAs

Arabidopsis thaliana transcriptomes have been extensively studied and characterized under different conditions. However, most of the current ‘RNA-sequencing’ technologies produce a relatively short read length and demand a reverse-transcription step, preventing effective characterization of transcriptome complexity. Here, we performed Direct RNA Sequencing (DRS) using the latest Oxford Nanopore Technology (ONT) with exceptional read length. We demonstrate that the complexity of the A. thaliana transcriptomes has been substantially under-estimated. The ONT direct RNA sequencing identified novel transcript isoforms at both the vegetative (14-day old seedlings, stage 1.04) and reproductive stages (stage 6.00–6.10) of development. Using in-house software called TrackCluster, we determined alternative transcription initiation (ATI), alternative polyadenylation (APA), alternative splicing (AS), and fusion transcripts. More than 38 500 novel transcript isoforms were identified, including six categories of fusion-transcripts that may result from differential RNA processing mechanisms. Aided by the Tombo algorithm, we found an enrichment of m5C modifications in the mobile mRNAs, consistent with a recent finding that m5C modification in mRNAs is crucial for their long-distance movement. In summary, ONT DRS offers an advantage in the identification and functional characterization of novel RNA isoforms and RNA base modifications, significantly improving annotation of the A. thaliana genome.

Factors facilitating sustainable scientific partnerships between developed and developing countries

International scientific partnerships are key to the success of strategic investments in plant science research and the farm-level adoption of new varieties and technologies, as well as the coherence of agricultural policies across borders to address global challenges. Such partnerships result not only in a greater impact of published research enhancing the career development of early and later stage researchers, but they also ensure that advances in plant science and crop breeding technologies make a meaningful contribution to society by brokering acceptance of emerging solutions to the world problems. We discuss the evidence showing that despite a lack of funding, scientists in some African countries make a significant contribution to global science output. We consider the criteria for success in establishing long-term scientific partnerships between scientists in developing countries in Southern Africa ("the South") and developed countries such as the UK ("the North"). We provide our own personal perspectives on the key attributes that lead to successful institutional collaborations and the establishment of sustainable networks of successful "North-South" scientific partnerships. In addition, we highlight some of the stumbling blocks which tend to hinder the sustainability of long-term "North-South" scientific networks. We use this personal knowledge and experiences to provide guidelines on how to establish and maintain successful long-term "North-South" scientific partnerships.

The coordination of guard-cell autonomous ABA synthesis and DES1 function in situ regulates plant water deficit responses

Introduction

Drought stress triggers the synthesis and accumulation of the phytohormone abscisic acid (ABA), which regulates stomatal aperture and hence reducing plant water loss. Hydrogen sulfide (H₂S), which is produced by the enzyme L-cysteine desulfhydrase 1 (DES1) that catalyzes the desulfuration of L-cysteine in Arabidopsis, also plays a critical role in the regulation of drought-induced stomatal closure. However, little is known about the regulation of DES1 or the crosstalk between H₂S and ABA signaling in response to dehydration.

Objectives

To demonstrate the potential crosstalk between DES1-dependent H₂S and ABA signaling in response to dehydration and its regulation mechanism.

Methods

Firstly, by introducing guard cell-specific MYB60 promoter, to produce complementary lines of DES1 or ABA3 into guard cell of des1 or aba3 mutant. And the related genes expression and water loss under ABA, NaHS, or dehydration treatment in these mutant or transgenics lines were determinate.

Results

We found that dehydration-induced expression of DES1 is abolished in the abscisic acid deficient 3 (aba3) mutants that are deficient in ABA synthesis. Both the complementation of ABA3 expression in guard cells of the aba3 mutants and ABA treatment rescue the dehydration-induced expression of DES1, as well as the wilting phenotype observed in these mutants. Moreover, the drought-induced expression of ABA synthesis genes was suppressed in des1 mutants. While the addition of ABA or the expression of either ABA3 or DES1 in the guard cells of the aba3/des1 double mutant did not alter the wilting phenotype of these mutants, the wild type phenotype was fully restored by the expression of both ABA3 and DES1, or by the application of NaHS.

Conclusion

These results demonstrate that the coordinated synthesis of ABA and DES1 expression is required for drought-induced stomatal closure in Arabidopsis.