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Plants are phytochemical hubs containing antioxidants, essential for normal plant functioning and adaptation to environmental cues and delivering beneficial properties for human health. Therefore, knowledge on the antioxidant potential of different plant species and their nutraceutical and pharmaceutical properties is of utmost importance. Exploring this scientific research field provides fundamental clues on (1) plant stress responses and their adaptive evolution to harsh environmental conditions and (2) (new) natural antioxidants with a functional versatility to prevent and treat human pathologies. These natural antioxidants can be valorized via plant-derived foods and products. Cuba contains an enormously rich plant biodiversity harboring a great antioxidant potential. Besides opening new avenues for the implementation of sustainable agroecological practices in crop production, it will also contribute to new strategies to preserve plant biodiversity and simultaneously improve nature management policies in Cuba. This review provides an overview on the beneficial properties of antioxidants for plant protection and human health and is directed to the valorization of these plant antioxidants, emphasizing the need for biodiversity conservation. This research was funded by VLIR-IUC, grant number CU2019IUC030A105-77143 and VLIR-TEAM, grant number CU2017TEA433A102. Cuypers, A (corresponding author), Hasselt Univ, Ctr Environm Sci, Campus Diepenbeek,Agoralaan Bldg D, BE-3590 Diepenbeek, Belgium. Cos, P (corresponding author), Univ Antwerp, Lab Microbiol Parasitol & Hyg LMPH, Univ Pl 1, BE-2610 Antwerp, Belgium. gabriel@uo.edu.cu; daniel.mendez@reduc.edu.cu; sophie.hendrix@uhasselt.be; jcea@uo.edu.cu; yilan@uo.edu.cu; aochoap@uo.edu.cu; jgadi@uo.edu.cu; jquevedo@uo.edu.cu; albys@uo.edu.cu; elizabetha@uo.edu.cu; natalie.beenaerts@uhasselt.be; isidro.mendez@reduc.edu.cu; torbera@uo.edu.cu; paul.cos@uantwerpen.be; ann.cuypers@uhasselt.be

Anthropogenic pollution of agricultural soils with cadmium (Cd) should receive adequate attention as Cd accumulation in crops endangers human health. When Cd is present in the soil, plants are exposed to it throughout their entire life cycle. As it is a non-essential element, no specific Cd uptake mechanisms are present. Therefore, Cd enters the plant through transporters for essential elements and consequently disturbs plant growth and development. In this review, we will focus on the effects of Cd on the most important events of a plant's life cycle covering seed germination, the vegetative phase and the reproduction phase. Within the vegetative phase, the disturbance of the cell cycle by Cd is highlighted with special emphasis on endoreduplication, DNA damage and its relation to cell death. Furthermore, we will discuss the cell wall as an important structure in retaining Cd and the ability of plants to actively modify the cell wall to increase Cd tolerance. As Cd is known to affect concentrations of reactive oxygen species (ROS) and phytohormones, special emphasis is put on the involvement of these compounds in plant developmental processes. Lastly, possible future research areas are put forward and a general conclusion is drawn, revealing that Cd is agonizing for all stages of plant development. This work was supported by the Research Foundation Flanders (FWO) by project funding for M.H. [G0B6716], S.H. [G0C7518CUY], M.J. [SBOS000119N], J.D. [FWO PhD grant], and bijzonder onderzoeksfonds (BOF) from Hasselt University to V.I. [BOF-18D02CUYA] and S.V. [PhD grant].

Environmental contamination with metals and organic compounds poses a serious threat to human health. Investigating plant responses to these contaminants at the molecular and cellular level is crucial to optimize phytoremediation strategies to clean up contaminated soils. Two key players in plant stress responses are the sulphur-containing amino acids cysteine and methionine. Cysteine is an important constituent of the metal-chelating metallothioneins and is also the precursor for glutathione and subsequent phytochelatin synthesis. During stress conditions, glutathione is involved in (1) metal chelation, (2) xenobiotic detoxification and (3) antioxidative defence. The activated form of methionine, S-adenosylmethionine, is involved in the synthesis of ethylene and polyamines, both playing important roles in signal transduction. This review provides an overview of sulphur uptake and assimilation and its conversion into basic metabolites essential for detoxification and signal transduction during metal and organic contaminant exposure in plants. Furthermore, the cross talk between these pathways and their relation to the contaminant-induced oxidative challenge are discussed.

Plants exposed to excess metals are challenged by an increased generation of reactive oxygen species (ROS) such as superoxide (O-2(center dot-)), hydrogen peroxide (H2O2) and the hydroxyl radical ((OH)-O-center dot). The mechanisms underlying this oxidative challenge are often dependent on metal-specific properties and might play a role in stress perception, signaling and acclimation. Although ROS were initially considered as toxic compounds causing damage to various cellular structures, their role as signaling molecules became a topic of intense research over the last decade. Hydrogen peroxide in particular is important in signaling because of its relatively low toxicity, long lifespan and its ability to cross cellular membranes. The delicate balance between its production and scavenging by a plethora of enzymatic and metabolic antioxidants is crucial in the onset of diverse signaling cascades that finally lead to plant acclimation to metal stress. In this review, our current knowledge on the dual role of ROS in metal-exposed plants is presented. Evidence for a relationship between H2O2 and plant metal tolerance is provided. Furthermore, emphasis is put on recent advances in understanding cellular damage and downstream signaling responses as a result of metal-induced H2O2 production. Finally, special attention is paid to the interaction between H2O2 and other signaling components such as transcription factors, mitogen-activated protein kinases, phytohormones and regulating systems (e.g. microRNAs). These responses potentially underlie metal-induced senescence in plants. Elucidating the signaling network activated during metal stress is a pivotal step to make progress in applied technologies like phytoremediation of polluted soils. This work was supported by the Research Foundation Flanders (FWO) by a postdoctoral grant for EK and projects [G0D3414] and [G0D11141]. Additional funding came from Hasselt University (BOF12NI28, BOF14DOC04) and PhD grants from the Agency for Innovation by Science and Technology (IWT-Flanders).

Besides their essential roles as substrates for carbon and energy metabolism, sugars also act in signal transduction, coordinating developmental and metabolic processes with nutrient availability. In animals, posttranslational modifications of nucleocytoplasmic proteins with β-N-acetylglucosamine (GlcNAc; an amide derivative of glucose) by O-GlcNac transfer-ase (OGT) play a key role in nutrient sensing (Liu et al. 2015). The Arabidopsis (Arabidopsis thaliana) genome encodes two OGT homologs: SECRET AGENT (SEC) and SPINDLY (SPY) (Sun 2021). Whereas SEC is a canonical OGT, SPY catalyzes protein O-fucosylation using GDP-fucose (a nucleotide sugar derived from GDP-mannose) as a substrate. SPY was initially identified as a negative regulator of gib-berellin signaling and its importance for plant growth is underlined by the range of developmental defects observed in Arabidopsis spy mutants, which are generally more pronounced than those in sec mutants (Jacobsen and Olszewski 1993; Hartweck et al. 2002; Sun 2021). Recent studies identified a small number of SPY-interacting proteins, which were involved in hormone signaling, circadian clock function, as well as the regulation of transcription and RNA splicing. However, these only represented the tip of the iceberg among SPY targets, as has become apparent now. In this issue of The Plant Cell, Yang Bi, Ruben Shrestha and colleagues (Bi et al. 2023) identified a large number of O-fucosylated proteins from Arabidopsis by affinity purification. The authors first showed that spy mutants grew poorly on sucrose-supplemented media in the dark (see Figure), indicating a crucial role for SPY in sugar-dependent growth. To identify targets of SPY-mediated O-fucosylation, they developed an affinity chromatography method utilizing Aleuria aurantia lectin (AAL), which specifically binds to O-fucose (Bandini et al. 2016). A proteome-wide screen in wild-type plants using AAL affinity chromatography followed by mass spectrometry identified 943 O-fucosylated peptides originating from 467 different proteins. O-fucosylated pep-tides were either undetectable or found in strongly reduced levels in spy mutants (see Figure), supporting the idea that SPY is the only protein O-fucosyltransferase catalyzing terminal O-fucosylation in Arabidopsis. According to the sub-cellular localization database SUBA4.0 (https://suba.live/), almost 67% of the identified proteins had a predicted nuclear localization, and only 12% and 9% were predicted to be localized in the cytosol and plastids, respectively. By contrast, O-fucosylation in metazoans is found only in secreted and cell surface proteins and is catalyzed by ER-localized O-fucosyltransferases (Sun 2021). The results confirmed several previously reported SPY in-teractors including the DELLA protein RGA and the bHLH transcription factors TCP14 and TCP15, supporting the validity of the affinity chromatography approach. Gene ontology analysis showed significant enrichment of key molecular functions such as histone modification, transcription, RNA processing, translation, protein degradation and phosphoryl-ation, the cytoskeleton, and vesicle trafficking among O-fucosylation targets. Interestingly, several of the identified proteins are also proposed targets of SEC and/or TARGET OF RAPAMYCIN (TOR), providing evidence for the integration In Brief

The increasing occurrence of heat waves due to climate change forms a major threat to global food security because high temperatures negatively impact plant growth and crop yield (Bailey-Serres et al. 2019). Hence, it is crucial to increase our knowledge of the molecular mechanisms underlying plant responses to heat stress to hasten the development of strategies to enhance plant thermotolerance. In Arabidopsis thaliana, class A1 heat stress transcription factors (HSFA1s) function as master regulators of heat stress responses. HSFA1s transcrip-tionally induce HSFA2, which in turn controls the expression of many heat-responsive genes, including those encoding heat shock proteins (HSPs) (Yoshida et al. 2011). In this issue, Jie Li and colleagues (Li et al. 2023) identify the role of a miR165/166-PHABULOSA (PHB) module in tran-scriptional and posttranslational regulation of HSFA1s (see Fig.). The highly conserved miRNAs miR165/166 regulate a variety of cellular processes by controlling transcript levels of Class III HD-ZIP transcription factors, such as PHB and PHAVOLUTA (PHV), which are important regulators of radial patterning in shoots (McConnell et al. 2001). In the first set of experiments, the authors showed that heat stress strongly induced the expression of miR165/166, leading to decreased transcript levels of PHB and PHV. To further explore the role of these 4 genes in heat stress responses, several transgenic lines were grown on agar plates or soil at ambient temperature and then subjected to a temperature of 37 °C. Whereas transgenic lines overexpressing miR165/ 166 and a phb phv double mutant displayed a higher thermo-tolerance compared with wild-type plants, the opposite was observed for miR165/166 knockdown lines and plants expressing a miR165/166 cleavage-resistant form of PHB. Chromatin immunoprecipitation and electrophoretic mobility shift assays revealed that both HSFA1a and HSFA1b are direct PHB targets, and a dual-luciferase assay showed that their expression is negatively regulated by PHB. Together, these data suggest an important role of the miR165/ 166-PHB module in transcriptional control of plant heat stress responses. RNA-sequencing experiments then confirmed that many heat stress-responsive genes, including HSFA2, were downregulated in plants expressing a miR165/ 166 cleavage-resistant form of PHB and in miR165/166 knockdown lines and were upregulated in miR165/ 166-overexpressing lines. Interestingly, PHB was shown to directly bind to the HSFA2 promoter and negatively affect HSFA2 expression, indicating that HSFA2 is a common target of both PHB and HSFA1s. In the next part of the study, the authors demonstrated that PHB also controls HSFA1s at the posttranslational level. Using a combination of in vitro and in vivo approaches, they showed that PHB physically interacts with both HSFA1a and HSFA1b. PHB had an antagonistic effect on HSFA1b tran-scriptional activity by interfering with its DNA binding ability. Transcriptional responses to heat stress were similar between seedlings expressing a miR165/166 cleavage-resistant form of PHB and an hsfa1 quadruple mutant, indicating that PHB and HSFA1s coregulate transcriptional reprogramming in response to heat stress. A final set of experiments revealed that the miR165/166-PHB module functions upstream of HSFA1s because the enhanced thermotolerance of transgen-ic lines overexpressing miR165/166 was suppressed in a hsfa1a hsfa1b hsfa1d triple mutant. In conclusion, this study established the importance of the miR165/166-PHB module in plant heat stress responses and identified miRNAs as potential targets to enhance plant ther-motolerance. However, the molecular mechanisms functioning upstream of the miR165/166-PHB module remain to be In Brief

When we find ourselves in danger, we tend to run away and cry for help. Plants are rooted into the ground, so that's it; or is it? In fact, they have developed intricate mechanisms to minimize stress exposure and its negative consequences. When growing in a polluted environment, they can redirect their root growth toward less polluted soil patches. Similarly, morphological alterations enhance leaf cooling when ambient temperatures increase. And although plants do not speak or cry for help, they do warn their neighbors of lurking danger and communicate with each other. Indeed, underground communication can occur between plants through mycorrhizal networks, while the emission of volatile compounds allows plants to send signals aboveground (Karban, 2021). In this issue, Magdalena Szechy nska-Hebda, Maria Lewandowska, and colleagues (Szechy nska-Hebda et al., 2022) show that plants can also directly communicate when their leaves touch, thereby mediating network acquired acclimation (see Figure). This newly discovered phenomenon relies on electrical, reactive oxygen species (ROS), and calcium signals, which are also the protagonists in the previously described systemic acquired accli-mation (Karpinski et al., 1999; Szechy nska-Hebda et al., 2010; Fichman and Mittler, 2021). To study direct aboveground plant-to-plant communication , the authors used dandelion (Taraxacum officinale) as a model. They showed that heat-induced injury of one dandelion leaf resulted in higher non-photochemical quenching (NPQ) in the immediate surroundings of the injury site. The response then spread to distal leaf areas in a wave-like fashion, indicating systemic signaling. Notably, signal propagation was not restricted to tissues within the same plant, but also extended to leaves of a second dandelion plant when it was connected to the injured plant via a drop of water. The transmission of this rise in NPQ coincided with the propagation of electrical and ROS signals between the leaves of the two plants. When the drop connecting the two plants contained the calcium antagonist lanthanum chloride, injury-induced increases in ROS levels were blocked in both the transmitter and receiver plants, pointing to a role for calcium channels in this signal transduction. The authors hypothesized that electrical signals are the main conduits of this aboveground communication pathway, as they observed responses in receiver plants when plants were connected through a copper wire, which can transmit electrical signals but not ROS. These injury-induced signals appeared to also be transmitted from a primary receiver to a secondary receiver plant when arranged in a two-chain system, indicating that communication can extend over an entire network of touching plants. Such communication networks likely contribute to stress acclimation, as signals from a heat-injured leaf of a transmitter plant influenced the acclimation responses of receiver plant leaves to subsequent excess light exposure. Importantly, signaling also took place between dandelion and Arabidopsis (Arabidopsis thaliana) or Mimosa (Mimosa pudica) leaves connected by a copper wire, suggesting that different plant species can communicate through a universal electrical language. To further investigate the newly identified communication system at the molecular level, the authors switched to In Brief