Tree transpiration dynamics and mechanisms in karst habitats are not fully understood due to the heterogeneous environmental features and complex species composition. Two common coexisting tree species, Mallotus philippensis and Celtis biondii, were examined in soil- and rock-dominated (SD and RD) karst habitats. Soil moisture, plant transpiration, root distribution, and leaf water potential were measured over two years (2021 and 2022). The mean water content was significantly lower in the RD than in the SD habitat. Transpiration patterns also differed between habitats, although species-specific distinctions were driven by leaf and root physiological traits. M. philippensis showed an isohydric tendency in both habitats and a lower density of fine roots, mostly in the soil zone, in the RD habitat. The transpiration of M. philippensis followed the variation in soil moisture, being lower in the RD habitat. Conversely, an anisohydric tendency in both habitats and a higher density of fine roots in both the soil and bedrock zones in the RD habitat were found in C. biondii. This species showed higher transpiration in the RD habitat, arising from ample water availability from soil and epikarst. Our findings reveal the regulatory mechanisms of species-specific root-zone water availability in transpiration patterns across karst habitats.

Peach Leaf Curl Disease, caused by the fungus Taphrina deformans, is characterized by reddish hypertrophic and hyperplasic leaf areas. To comprehend the biochemical imbalances caused by the disease an integrated approach including metabolomics, lipidomics, proteomics and complementary biochemical techniques was undertaken. Symptomatic and asymptomatic areas were dissected from leaves with increasing extension of the disease. A differential metabolic behaviour was identified in symptomatic areas with respect to either asymptomatic areas or healthy leaves. Symptomatic areas showed an altered chloroplastic functioning and composition which includes decrease in the photosynthetic machinery, alteration in plastidic lipids, and decreased starch, carotenoid and chlorophyll biosynthesis. In symptomatic areas, decreases in chloroplast redox-homeostasis proteins and in triacylglycerols double bond index were observed. Proteomic data revealed an up-regulation of phenylpropanoid and mevalonate pathways and down-regulation of the plastidic methylerythritol phosphate route. Amino acid pools were affected, with up-regulation of proteins involved in asparagine synthesis. Curled areas exhibited a metabolic shift towards functioning as a sink tissue importing sugars and producing energy through fermentation and respiration and reductive power via the pentose phosphate route. As the disease progresses, reduced asymptomatic areas and healthy leaves diminishes photosynthates production thereby limiting fruit production and ultimately tree survival.

The root cortex is an important anatomical phenes, and root cortical senescence (RCS) is closely associated with root absorptive function. However, characteristics and responses of RCS to drought stress in cotton have received little attention. This study subjected the drought-tolerant cotton variety “Guoxin 02” and the drought-sensitive variety “Ji 228” to drought stress (8% PEF6000) and no-stress (0% PEG6000) treatments to determine the characteristics and responses of cotton RCS to drought stress. The results showed that the RCS of the two varieties was significantly promoted under drought stress. The greater the distance from the root tip, the more severe the RCS occurrence under drought stress compared with non-stress treatment. The occurrence of RCS in “Guoxin 02” highered by 14.03%-20.18% compared to “Ji 228” under drought stress. Moreover, the RCS was significantly negatively correlated with root respiration but significantly positively correlated with total root length and leaf water potential ( p < 0.05). Indole-3-acetic acid (IAA) content increased, while abscisic acid (ABA) content decreased as the RCS increased. In summary, endogenous hormones regulated the occurrence of RCS, which reduced the root metabolic costs and seemingly achieved more resource redistribution to new roots, thereby expanding the water absorption capacity of roots to fully utilize deep water resources. Thus, the study demonstrates the potential of RCS in improving the drought stress tolerance of cotton.

Early sowing can help summer crops escape drought and can mitigate the impacts of climate change on them, but it exposes them to cold stress during initial developmental stages, which has both immediate and long-term effects on development and physiology. To understand how early night-chilling stress impacts plant development and the yield, we studied the reference sunflower line XRQ under controlled, semi-controlled and field conditions. We performed high-throughput imaging of the whole plant parts and obtained physiological and transcriptomic data from leaves, hypocotyls and roots. We observed morphological reductions in early stages under field and controlled conditions, with a decrease in root development, an increase in reactive oxygen species content in leaves and changes in lipid composition in hypocotyls. A long-term increase in leaf chlorophyll suggests a stress memory mechanism that was supported by transcriptomic induction of histone coding genes. We highlighted leaf transcriptomes in cold-acclimation genes such as chaperone, heat shock and late embryogenesis abundant proteins. We identified genes in hypocotyls involved in lipid, cutin, suberin and phenylalanine ammonia lyase biosynthesis and ROS scavenging. This comprehensive study describes new phenotyping methods and candidate genes to understand phenotypic plasticity better in response to chilling and study stress memory in sunflower.

Plants are an intrinsic part of the soil community and the “one health concept” considers that human health is intimately connected to the health of animals, plants, and microbial environments. Plant-microbe interactions are a cornerstone of one health, the soil microbiome being comprised of a diverse range of organisms, interacts in the rhizosphere through continuous molecular communications. Soils are a source and reservoir of pathogens, as well as beneficial microorganisms. Hence, the molecular dialogue at the rhizosphere interface is crucial not only for successful plant-microbe interactions but also for crop resilience and stress tolerance. The plant-microbe continuum forms a network of underground “nutrient highways” that benefit both plant and microbial communities. It also serves as a significant sink for atmospheric CO 2. While microbial diversity is generally positively associated with one health, the host range of beneficial microbes currently limits their successful exploitation with a wide range of microbial communities. We consider the possibility of increasing the host range of beneficial microbes, including arbuscular mycorrhiza fungi (AMF) and rhizobia, and how current genetic incompatibility and/or activation of robust plant defenses, can be overcome while accepting that significant challenges exist in translating laboratory findings into the field. We consider why AMF inoculants and plant growth-promoting microbes are not always beneficial under field conditions and suggest possible approaches for tailoring plant-microbe interactions to assist plant breeding efforts in crop resilience.

Plant responses to multifactorial stress combinations are seldom studied, but combinations of abiotic and biotic stresses may cause drastic yield reductions in crops. While an abiotic stress, the salinization of agricultural soil, affects crop production, added pressures of insect herbivores could lead to further losses. In this paper, we investigate the effects of salinity on an insect herbivore, the corn earworm caterpillar ( Helicoverpa zea), feeding on tomato ( Solanum lycopersicum cv. Better Boy) plants. We show that salt-stressed tomato plants are poor hosts for H. zea, impacting caterpillar growth rates, caterpillar feeding preference, and moth oviposition. We further show that these observations are best explained by reductions in both relative leaf water content and leaf total protein content, along with ionic toxicity and imbalance. We observe that salt stress does not influence anti-insect herbivory defense protein (PPO and TPI) levels. Finally, we observe that salt treatment leads to differences in specific volatiles, with lower emissions of 2-carene, α-phellandrene, β-phellandrene, α-humulene, and β-caryophyllene in salt-treated plants. We demonstrate that salt exposure changes tomato plant quality and chemical composition, which in turn negatively affects insect herbivores feeding on these plants.

As a well-conserved histone variant, H2A.Z epigenetically regulates plant growth and development as well as the interaction with environmental factors. However, the role of H2A.Z in response to salt stress remains unclear, and whether nucleosomal H2A.Z occupancy work on the gene responsiveness upon salinity is obscure. Here, we elucidate the involvement of H2A.Z in salt response by analyzing H2A.Z disorder plants with impaired or overloaded H2A.Z deposition. The salt tolerance is dramatically accompanied by H2A.Z deficiency and reacquired in H2A.Z OE lines. H2A.Z disorder changes the expression profiles of large-scale of salt responsive genes, announcing that H2A.Z is required for plant salt response. Genome-wide H2A.Z mapping shows that H2A.Z level is induced by salt condition across promoter, TSS and TES (-1 kb to +1kb), the peaks preferentially enrich at promoter regions near TSS. We further show that H2A.Z deposition within TSS provides a direct role on transcriptional control, which has both repressive and activating effects, while it is found generally H2A.Z enrichment negatively correlate with gene expression level response to salt stress. This study shed light on the H2A.Z function in salt tolerance, highlighting the complex regulatory mechanisms of H2A.Z on transcriptional activity for yielding appropriate responses to particularly environmental stress.

Drought threatens plant growth and related ecosystem services. The emergence of plant drought stress under edaphic drought is well studied, whilst the importance of atmospheric drought only recently gained momentum. Yet, little is known about the interaction and relative contribution of edaphic and atmospheric drought on the emergence of plant drought stress. We conducted a gradient experiment, fully crossing gravimetric water content (GWC: field capacity-permanent wilting point) and vapour pressure deficit (VPD: 1-2.25kPa) using five wheat varieties from three species ( Triticum monococcum, T. durum & T. aestivum). We quantified the emergence of plant drought stress on molecular (ABA), cellular (stomatal conductance), organ (leaf water potential) and stand level (evapotranspiration). Plant drought stress increased with decreasing GWC across all organisational levels. This effect was magnified non-linearly by VPD after passing a critical threshold of soil water availability. At around 20% GWC plants lost their ability to regulate leaf water potential via stomata regulation, followed by the emergence of hydraulic dysfunction. The emergence of plant drought stress is characterized by changing relative contributions of soil vs. atmosphere and their non-linear interaction. This highly non-linear response, consequently, is likely to abruptly alter plant-related ecosystem services in a drying world.

Reactive oxygen species are important signaling molecules that influence many aspects of plant biology. One way in which ROS influence plant growth and development is by modifying intercellular trafficking through plasmodesmata (PD). Viruses have evolved to use plasmodesmata for their local cell-to-cell spread between plant cells, so it is therefore not surprising that they have found ways to modulate ROS and redox signaling to optimize plasmodesmata function for their benefit. This review examines how intracellular signaling via ROS and redox pathways regulate intercellular trafficking via PD during development and stress. The relationship between viruses and ROS-redox systems, and the strategies viruses employ to control PD function by interfering with ROS-redox in plants is also discussed.

Due to their stationery nature, plants are exposed to a diverse range of biotic and abiotic stresses, of which heavy metals stress poses as one of the most detrimental abiotic stresses, targeting crucial and vital processes. Heavy metals instigate the over-production of reactive oxygen species (ROS), and in order to mitigate the adverse effects of ROS, plants induce multiple defence mechanisms. Besides the negative implications of overproduction of ROS, these molecules play a multitude of signaling roles in plants, acting as a central player in the complex signaling network of cells. One of the signaling mechanisms it is involved in is the mitogen-activated protein kinase (MAPK) cascade, a signaling pathway used to transduce extracellular stimuli into intracellular responses. Plant MAPKs have been implicated in signaling of stresses, phytohormones and cell cycle cues. However, the influence of various heavy metals on MAPKs activation has not been well documented. In this review, we will attempt to address and summarize several aspects related to various heavy metal-induced ROS signaling, how these signals activate the MAPK cascade and the downstream transcription factors that instigates the plants response to these heavy metals. Moreover, we will highlight a modern research methodology that could characterize the novel genes associated with MAPKs and their roles in heavy metal stress.

Stomata play a pivotal role in regulating gas exchange between terrestrial plants and the atmosphere controlling water and carbon cycles at organismal, ecosystem and global levels. Accordingly, our objective was to investigate the impact of ultraviolet-B radiation, a neglected environmental factor varying with ongoing global change, on stomatal morphology and function by means of a comprehensive meta-analysis. We found 45 peer-reviewed publications containing altogether 143 case studies for analysis. The overall UV effect at the leaf level is to decrease stomatal conductance, stomatal aperture and stomatal size, although stomatal density was increased. The significant decline in conductance is marked in short-term experiments, with more modest decreases noted in long-term UV studies. We found that short-term experiments in growth chambers are not representative of long-term field UV effects on stomatal conductance. Further, we found a stronger UV effect in grasses than in herbs, while the reduction of stomatal conductance was insignificant in trees. It is hypothesised that these alterations in stomatal function have important potential consequences for plant life. In the short term, UV-mediated stomatal closure may reduce transpiration and alleviate drought stress. However, in the long term more complex changes in stomatal aperture, size and density may reduce carbon sink capacity, and enhance leaf and surface warming, potentially exacerbating the negative effects of drought and/or heatwaves on plant ecosystems and endangering long-term plant survival.

Summary: The hindrance of kernel development caused by waterlogging stress (WS) is the direct reason for the peanut yield reduction. Currently, the mechanism of kernel filling responding to WS remains unknown. The waterlogging-sensitive variety Huayu 39 was subjected to WS for 3 days after 7 days after gynophores touched the ground (DAG), and the key stage of WS affecting kernel filling is 14, 21, and 28 DAG. WS decreased the average filling rate and kernel dry weight. Therefore, transcriptome sequencing and widely-targeted metabolomic analysis were conducted on kernel to elucidate the mechanism for the decrease in average filling rate under WS, revealing that overexpression of the gene encoding tryptophan decarboxylase ( AhTDC), which caused the accumulation of melatonin, reduced kernel weight. The sucrose transformation rate was limited by the crosstalk between melatonin and ethylene, thereby reducing the kernel filling rate and hindering kernel development. Our results are crucial for formulating measures to alleviate the negative impact of WS on peanut yield and quality, providing a basis for exploring high-yield and high-quality cultivation, molecular-assisted breeding, and waterlogging prevention.

Xylem conduits have lignified walls to resist crushing pressures. The thicker the double-wall ( T) relative to its maximum diameter ( D), the greater the collapse/implosion resistance. Having xylem that is more resistant than necessary incurs high costs and reduced flow, while having xylem not resistant enough may lead to catastrophic collapse under drought. Despite the importance of xylem implosion safety in determining plant drought resistance, it is still unclear how leaves scale Tx D to trade-off among implosion safety, flow efficiency, mechanical support, and construction cost. We measured T and D in over 7,000 leaf xylem conduits of 122 ferns and angiosperms species to investigate how the Tx D scaling varies across species, clades, habitats, growth forms, and vein orders. Overall, leaf xylem conduits grow wider than thicker, potentially resulting in high flow efficiency and lower cost, but at the expense of high vulnerability to implosion. Conduits seem particularly vulnerable to implosion in monocots, aquatic species and in species from hydric habitats, as well as in major veins. The absence of strong trade-offs within the leaf functional traits examined suggests that implosion safety at the whole-leaf level cannot be easily predicted by the sum of the individual conduits’ resistance to collapse.

In plants, salicylic acid (SA) hydroxylation regulates SA homoeostasis, playing an essential role during plant development and response to pathogens. This reaction is catalyzed by SA hydroxylase enzymes, which hydroxylate SA producing 2,3- dihydroxybenzoic acid (2,3-DHBA) and/or 2,5-dihydroxybenzoic acid (2,5-DHBA). Several SA hydroxylases have been recently identified and characterized from different plant species; however, no such activity has been previously reported in maize. In this work, we describe the identification and characterization of a new SA hydroxylase in maize plants. This enzyme, with high sequence similarity to previously described SA hydroxylases from Arabidopsis and rice, converts SA into 2,5-DHBA; however, it shows different kinetics properties to those from previously characterized enzymes, and it also catalyzes the conversion of the flavonoid dihydroquercetin into quercetin in in vitro activity assays, suggesting that the maize enzyme may have different roles in vivo as those previously reported from other species. Despite this, ZmS5H can complement the resistance to pathogen and early senescence phenotypes of Arabidopsis s3h mutant plants. Finally, we characterized a maize mutant in the S5H gene ( s5hMu) that has altered growth, senescence and increased resistance against Colletotrichum graminicola infection, showing not only changes in SA and 2,5-DHBA but also variations in flavonol levels. Together, the results presented here provide evidence that SA hydroxylases in different plant species have evolved to show differences in catalytic properties that may be important to fine tune SA levels and other phenolic compounds such as flavonols to regulate different aspects of plant development and defense against pathogens.

The plant cell wall is a plastic structure of variable composition that constitutes the first line of defense against environmental challenges. Lodging and drought are two stressful conditions that severely impact on maize yield. In a previous work, we characterized the cell walls of two maize inbreds susceptible (EA2024) or resistant (B73) to stalk-lodging. Here, we show that drought induces phenotypical, physiological, cell wall, and transcriptional changes with distinct dynamics in the two inbreds, and that B73 is less tolerant than EA2024 to this stress. While in control conditions, stalk of EA2024 had higher levels of cellulose, uronic acids and p-coumarate than B73, upon drought these displayed increased levels of arabinose-enriched polymers, such as pectin-arabinans and arabinogalactan proteins, and a decreased lignin content. By contrast, a deeper rearrangement of cell walls including the modification of lignin composition and an increase of uronic acids was observed in B73. Drought induced higher changes in gene expression in B73 compared to EA2024, particularly in cell wall-related genes, that were altered in an inbred-specific manner. Transcription factor enrichment assays unveiled inbred-specific regulatory networks coordinating cell wall genes expression. Altogether, these findings reveal that B73 and EA2024 inbreds, with opposite stalk-lodging phenotypes, undertake different cell wall modification strategies in response to drought. We propose that the specific cell wall composition that confers lodging resistance to B73 compromises its cell wall plasticity and renders this inbred more susceptible to drought.

Nucleotide-binding, leucine-rich repeat (NLR) genes play a pivotal role in shaping plant effector-triggered immunity in response to pathogen invasions. However, the mechanisms governing the expression and behavior of NLRs, particularly in the context of head-to-head NLR gene pairs, in the presence of pathogens, remain uncovered. In this study, we dissected the Pik-H4 promoter (P Pik-H4) at the TATA boxes and conducted an in-depth investigation into split promoter activity using Agro-infiltration assays. The segments spanning 593-1232 bp and 2016-2492 bp (starting from -1 bp of Pik1-H4) within P Pik-H4 emerged as core regions for expressing Pik1-H4 and Pik1-H4 respectively. Nevertheless, merging these two core fragments failed to recover the promoter activity in both directions. Employing Gus staining, promoter activity assays and qRT-PCR, we unveiled the co-expression of Pik1-H4 and Pik2-H4 throughout the whole plant. Additionally, in the presence of the rice blast fungus, their co-amplification was observed in leaves and leaf sheaths. Strikingly, Pik-H4 exhibited heightened expression within vascular bundles. Moreover, perturbing the Pik1-H4 and Pik2-H4 co-expression relationship via overexpression in rice or Nicotiana did not disrupt the immune response. Upon infection, the singleton Pik 1-H4 localized within vesicles, while Pik 2-H4 predominantly occupied the nucleus within leaf sheath cells. Transcriptome analysis highlighted Pik-H4-mediated resistance triggering a transcriptome reprogramming between 12 and 24 hours post-inoculation. Notably, overexpression of Pik1-H4 or Pik2-H4 enriches various pathways compared to the Pik-H4 Lijiangheituanxingu near-isogenic lines. In summary, these findings unravel the intricate dynamics of co-expression and singular functionality within NLR bidirectional gene pairs upon pathogen invasion.

High temperature negatively impacts the yield and quality of fruit crops. Exogenous melatonin (MT) application has shown the capability to enhance heat tolerance, but the response of endogenous MT to heat stress, particularly in perennial fruit trees, remains elusive. This study investigated the effects of high temperatures on transgenic apple plants overexpressing the MT biosynthetic gene N-acetylserotonin methyltransferase 9 ( MdASMT9). Endogenous MT protected transgenic plants from heat stress, scavenging reactive oxygen species (ROS) and increasing soluble carbohydrates and amino acids levels. MdASMT9-overexpressing plants also maintained higher photosynthetic activity by protecting the chloroplasts from damage. Transcriptome sequencing indicates that MdASMT9 overexpression promoting the expression of HSFA1d, HSFA2-like, and HSFA9b, and inhibiting the transcription of HSFB1 and HSFB2b. Application of MT and overexpression of MdASMT9 reduced abscisic acid (ABA) accumulation through promoting MdWRKY33-mediated transcriptional inhibition of MdNCED1 and MdNCED3, thus promoting stomatal opening for better heat dissipation. Furthermore, melatonin enhanced autophagic activity through promoting MdWRKY33-mediated transcriptional enhancement of MdATG18a under heat stress . These findings provide new sight into the regulation of endogenous MT and its role in improving heat tolerance in perennial fruit trees.

Photosynthesis is the foundation of all life on Earth, providing oxygen and energy. However, if not well regulated, it can also generate toxic reactive oxygen species (ROS), which can cause photodamage. Regulation of photosynthesis is highly dynamic, responding to both environmental and metabolic cues, and occurs at many levels, from light capture to energy storage and metabolic processes. One general mechanism of regulation involves the reversible oxidation and reduction of protein thiol groups, which can affect the activity of enzymes and the stability of proteins. Such redox regulation has been well studied in stromal enzymes, but more recently evidence has emerged of redox control of thylakoid lumenal enzymes. This review/hypothesis paper summarizes the latest research and discusses several open questions and challenges to achieving effective redox control in the lumen, focusing on the distinct environments and regulatory components of the thylakoid lumen, including the need to transport electrons across the thylakoid membrane, the effects of pH changes in the stromal and lumenal compartments, and the observed differences in redox states. These constraints suggest that activated oxygen species are likely to be major regulatory contributors to lumenal thiol redox regulation, with key components and processes yet to be discovered.