The translocation of a chloride channel from the Golgi to the plasma membrane helps plants adapt to salt stress.

A key mechanism employed by plants to adapt to salinity stress involves maintaining ion homeostasis via the actions of ion transporters. While the function of cation transporters in maintaining ion homeostasis in plants has been extensively studied, little is known about the roles of their anion counterparts in this process. Here, we describe a mechanism of salt adaptation in plants. We characterized the chloride channel (CLC) gene AtCLCf, whose expression is regulated by WRKY transcription factor under salt stress in Arabidopsis thaliana. Loss-of-function atclcf seedlings show increased sensitivity to salt, whereas AtCLCf overexpression confers enhanced resistance to salt stress. Salt stress induces the translocation of GFP-AtCLCf fusion protein to the plasma membrane (PM). Blocking AtCLCf translocation using the exocytosis inhibitor brefeldin-A or mutating the small GTPase gene AtRABA1b/BEX5 (RAS GENES FROM RAT BRAINA1b homolog) increases salt sensitivity in plants. Electrophysiology and liposome-based assays confirm the Cl-/H+ antiport function of AtCLCf. Therefore, we have uncovered a mechanism of plant adaptation to salt stress involving the NaCl-induced translocation of AtCLCf to the PM, thus facilitating Cl- removal at the roots, and increasing the plant's salinity tolerance.

A high-affinity potassium transporter (MeHKT1) from cassava (Manihot esculenta) negatively regulates the response of transgenic Arabidopsis to salt stress.

BACKGROUND: High-affinity potassium transporters (HKTs) are crucial in facilitating potassium uptake by plants. Many types of HKTs confer salt tolerance to plants through regulating K+ and Na+ homeostasis under salinity stress. However, their specific functions in cassava (Manihot esculenta) remain unclear. RESULTS: Herein, an HKT gene (MeHKT1) was cloned from cassava, and its expression is triggered by exposure to salt stress. The expression of a plasma membrane-bound protein functions as transporter to rescue a low potassium (K+) sensitivity of yeast mutant strain, but the complementation of MeHKT1 is inhibited by NaCl treatment. Under low K+ stress, transgenic Arabidopsis with MeHKT1 exhibits improved growth due to increasing shoot K+ content. In contrast, transgenic Arabidopsis accumulates more Na+ under salt stress than wild-type (WT) plants. Nevertheless, the differences in K+ content between transgenic and WT plants are not significant. Additionally, Arabidopsis expressing MeHKT1 displayed a stronger salt-sensitive phenotype. CONCLUSION: These results suggest that under low K+ condition, MeHKT1 functions as a potassium transporter. In contrast, MeHKT1 mainly transports Na+ into cells under salt stress condition and negatively regulates the response of transgenic Arabidopsis to salt stress. Our results provide a reference for further research on the function of MeHKT1, and provide a basis for further application of MeHKT1 in cassava by molecular biological means.

A network-based modeling framework reveals the core signal transduction network underlying high carbon dioxide-induced stomatal closure in guard cells.

Stomata are pores on plant aerial surfaces, each bordered by a pair of guard cells. They control gas exchange vital for plant survival. Understanding how guard cells respond to environmental signals such as atmospheric carbon dioxide (CO2) levels is not only insightful to fundamental biology but also relevant to real-world issues of crop productivity under global climate change. In the past decade, multiple important signaling elements for stomatal closure induced by elevated CO2 have been identified. Yet, there is no comprehensive understanding of high CO2-induced stomatal closure. In this work, we assemble a cellular signaling network underlying high CO2-induced stomatal closure by integrating evidence from a comprehensive literature analysis. We further construct a Boolean dynamic model of the network, which allows in silico simulation of the stomatal closure response to high CO2 in wild-type Arabidopsis thaliana plants and in cases of pharmacological or genetic manipulation of network nodes. Our model has a 91% accuracy in capturing known experimental observations. We perform network-based logical analysis and reveal a feedback core of the network, which dictates cellular decisions in closure response to high CO2. Based on these analyses, we predict and experimentally confirm that applying nitric oxide (NO) induces stomatal closure in ambient CO2 and causes hypersensitivity to elevated CO2. Moreover, we predict a negative regulatory relationship between NO and the protein phosphatase ABI2 and find experimentally that NO inhibits ABI2 phosphatase activity. The experimental validation of these model predictions demonstrates the effectiveness of network-based modeling and highlights the decision-making role of the feedback core of the network in signal transduction. We further explore the model's potential in predicting targets of signaling elements not yet connected to the CO2 network. Our combination of network science, in silico model simulation, and experimental assays demonstrates an effective interdisciplinary approach to understanding system-level biology.

Expressing banana transcription factor MaERFVII3 in Arabidopsis confers enhanced waterlogging tolerance and root growth.

Background: Waterlogging poses a significant threat to plant growth and yield worldwide. Identifying the genes responsible for mitigating waterlogging stress is crucial. Ethylene-responsive factors (ERFs) are transcriptional regulators that respond to various biotic and abiotic stresses in plants. However, their roles and involvement in responding to waterlogging stress remain largely unexplored. Hence, this study aimed to elucidate the role of ERFs in enhancing banana plant resilience to waterlogging. Methods: We hypothesized that introducing a group VII ERF transcription factor in Arabidopsis could enhance waterlogging stress tolerance. To test this hypothesis, we isolated MaERFVII3 from banana roots, where it exhibited a significant induction in response to waterlogging stress. The isolated MaERFVII3 was introduced into Arabidopsis plants for functional gene studies. Results: Compared with wild-type plants, the MaERFVII3-expressing Arabidopsis showed increased survival and biomass under waterlogging stress. Furthermore, the abundance of transcripts related to waterlogging and hypoxia response showed an elevation in transgenic plants but a decrease in wild-type and empty vector plants when exposed to waterlogging stress. Our results demonstrate the significant contribution of MaERFVII3 to waterlogging tolerance in Arabidopsis, providing baseline data for further exploration and potentially contributing to crop improvement programs.

H2S is involved in drought-mediated stomatal closure through PLDα1 in Arabidopsis.

MAIN CONCLUSION: PLDα1 promoted H2S production by positively regulating the expression of LCD. Stomatal closure promoted by PLDα1 required the accumulation of H2S under drought stress. Phospholipase Dα1 (PLDα1) acting as one of the signal enzymes can respond to drought stress. It is well known that hydrogen sulfide (H2S) plays an important role in plant responding to biotic or abiotic stress. In this study, the functions and relationship between PLDα1 and H2S in drought stress resistance in Arabidopsis were explored. Our results indicated that drought stress promotes PLDα1 and H2S production by inducing the expression of PLDα1 and LCD genes. PLDα1 and LCD enhanced plant tolerance to drought by regulating membrane lipid peroxidation, proline accumulation, H2O2 content and stomatal closure. Under drought stress, the H2O2 content of PLDα1-deficient mutant (pldα1), L-cysteine desulfhydrase (LCD)-deficient mutant (lcd) was higher than that of ecotype (WT), the stomatal aperture of pldα1 and lcd was larger than that of WT. The transcriptional and translational levels of LCD were lower in pldα1 than that in WT. Exogenous application of the H2S donor NaHS or GYY reduced the stomatal aperture of WT, pldα1, PLDα1-CO, and PLDα1-OE lines, while exogenous application of the H2S scavenger hypotaurine (HT) increased the stomatal aperture. qRT-PCR analysis of stomatal movement-related genes showed that the expression of CAX1, ABCG5, SCAB1, and SLAC1 genes in pldα1 and lcd were down-regulated, while ACA1 and OST1 gene expression was significantly up-regulated. Thus, PLDα1 and LCD are required for stomatal closure to improve drought stress tolerance.

Investigation of Arabidopsis root skototropism with different distance settings.

Plants can activate protective and defense mechanisms under biotic and abiotic stresses. Their roots naturally grow in the soil, but when they encounter sunlight in the top-soil layers, they may move away from the light source to seek darkness. Here we investigate the skototropic behavior of roots, which promotes their fitness and survival. Glutamate-like receptors (GLRs) of plants play roles in sensing and responding to signals, but their role in root skototropism is not yet understood. Light-induced tropisms are known to be affected by auxin distribution, mainly determined by auxin efflux proteins (PIN proteins) at the root tip. However, the role of PIN proteins in root skototropism has not been investigated yet. To better understand root skototropism and its connection to the distance between roots and light, we established five distance settings between seedlings and darkness to investigate the variations in root bending tendencies. We compared differences in root skototropic behavior across different expression lines of Arabidopsis thaliana seedlings (atglr3.7 ko, AtGLR3.7 OE, and pin2 knockout) to comprehend their functions. Our research shows that as the distance between roots and darkness increases, the root's positive skototropism noticeably weakens. Our findings highlight the involvement of GLR3.7 and PIN2 in root skototropism.

Variation and plasticity in life-history traits and fitness of wild Arabidopsis thaliana populations are not related to their genotypic and ecological diversity.

BACKGROUND: Despite its implications for population dynamics and evolution, the relationship between genetic and phenotypic variation in wild populations remains unclear. Here, we estimated variation and plasticity in life-history traits and fitness of the annual plant Arabidopsis thaliana in two common garden experiments that differed in environmental conditions. We used up to 306 maternal inbred lines from six Iberian populations characterized by low and high genotypic (based on whole-genome sequences) and ecological (vegetation type) diversity. RESULTS: Low and high genotypic and ecological diversity was found in edge and core Iberian environments, respectively. Given that selection is expected to be stronger in edge environments and that ecological diversity may enhance both phenotypic variation and plasticity, we expected genotypic diversity to be positively associated with phenotypic variation and plasticity. However, maternal lines, irrespective of the genotypic and ecological diversity of their population of origin, exhibited a substantial amount of phenotypic variation and plasticity for all traits. Furthermore, all populations harbored maternal lines with canalization (robustness) or sensitivity in response to harsher environmental conditions in one of the two experiments. CONCLUSIONS: Overall, we conclude that the environmental attributes of each population probably determine their genotypic diversity, but all populations maintain substantial phenotypic variation and plasticity for all traits, which represents an asset to endure in changing environments.

The Arabidopsis Mitochondrial Nucleoid-Associated Protein WHIRLY2 Is Required for a Proper Response to Salt Stress.

In the last years, plant organelles have emerged as central coordinators of responses to internal and external stimuli, which can induce stress. Mitochondria play a fundamental role as stress sensors being part of a complex communication network between the organelles and the nucleus. Among the different environmental stresses, salt stress poses a significant challenge and requires efficient signaling and protective mechanisms. By using the why2 T-DNA insertion mutant and a novel knock-out mutant prepared by CRISPR/Cas9-mediated genome editing, this study revealed that WHIRLY2 is crucial for protecting mitochondrial DNA (mtDNA) integrity during salt stress. Loss-of-function mutants show an enhanced sensitivity to salt stress. The disruption of WHIRLY2 causes the impairment of mtDNA repair that results in the accumulation of aberrant recombination products, coinciding with severe alterations in nucleoid integrity and overall mitochondria morphology besides a compromised redox-dependent response and misregulation of antioxidant enzymes. The results of this study revealed that WHIRLY2-mediated structural features in mitochondria (nucleoid compactness and cristae) are important for an effective response to salt stress.

Light-dependent chloroplast relocation in wild strawberry (Fragaria vesca).

Chloroplast photorelocation is a vital organellar response that optimizes photosynthesis in plants amid fluctuating environmental conditions. Chloroplasts exhibit an accumulation response, in which they move toward weak light to enhance photoreception, and an avoidance response, in which they move away from strong light to avoid photodamage. Although chloroplast photorelocation has been extensively studied in model plants such as Arabidopsis thaliana, little is known about this process in the economically important crop strawberry. Here, we investigated chloroplast photorelocation in leaf mesophyll cells of wild strawberry (Fragaria vesca), a diploid relative of commercially cultivated octoploid strawberry (F. × ananassa). Microscopy observation revealed that the periclinal area of leaf mesophyll cells in F. vesca is considerably smaller than that of A. thaliana. Given this small cell size, we investigated chloroplast photorelocation in F. vesca by measuring light transmittance in leaves. Weak blue light induced the accumulation response, whereas strong blue light induced the avoidance response. Unexpectedly, strong red light also induced the accumulation response in F. vesca. These findings shed light on chloroplast photorelocation as an intracellular response, laying the foundation for enhancing photosynthesis and productivity in Fragaria.

RotatedStomataNet: a deep rotated object detection network for directional stomata phenotype analysis.

KEY MESSAGE: Innovatively, we consider stomatal detection as rotated object detection and provide an end-to-end, batch, rotated, real-time stomatal density and aperture size intelligent detection and identification system, RotatedeStomataNet. Stomata acts as a pathway for air and water vapor in the course of respiration, transpiration, and other gas metabolism, so the stomata phenotype is important for plant growth and development. Intelligent detection of high-throughput stoma is a key issue. Nevertheless, currently available methods usually suffer from detection errors or cumbersome operations when facing densely and unevenly arranged stomata. The proposed RotatedStomataNet innovatively regards stomata detection as rotated object detection, enabling an end-to-end, real-time, and intelligent phenotype analysis of stomata and apertures. The system is constructed based on the Arabidopsis and maize stomatal data sets acquired destructively, and the maize stomatal data set acquired in a non-destructive way, enabling the one-stop automatic collection of phenotypic, such as the location, density, length, and width of stomata and apertures without step-by-step operations. The accuracy of this system to acquire stomata and apertures has been well demonstrated in monocotyledon and dicotyledon, such as Arabidopsis, soybean, wheat, and maize. The experimental results that the prediction results of the method are consistent with those of manual labeling. The test sets, the system code, and their usage are also given ( https://github.com/AITAhenu/RotatedStomataNet ).

Evolutionary potential under heat and drought stress at the southern range edge of North American Arabidopsis lyrata.

The warm edges of species' distributions are vulnerable to global warming. Evidence is the recent range retraction from there found in many species. It is unclear why populations cannot easily adapt to warmer, drier, or combined hot and dry conditions and locally persist. Here, we assessed the ability to adapt to these stressors in the temperate species Arabidopsis lyrata. We grew plants from replicate seed families of a central population with high genetic diversity under a temperature and precipitation regime typical of the low-latitude margin or under hotter and/or drier conditions within naturally occurring amplitudes. We then estimated genetic variance-covariance (G-) matrices of traits depicting growth and allocation as well as selection vectors to compare the predicted adaptation potential under the different climate-stress regimes. We found that the sum of genetic variances and genetic correlations were not significantly different under stress as compared to benign conditions. However, under drought and heat drought, the predicted ability to adapt was severely constrained due to strong selection and selection pointing in a direction with less multivariate genetic variation. The much-reduced ability to adapt to dry and hot-dry conditions is likely to reduce the persistence of populations at the low-latitude margin of the species' distribution and contribute to the local extinction of the species under further warming.

RhMED15a-like, a subunit of the Mediator complex, is involved in the drought stress response in Rosa hybrida.

BACKGROUND: Rose (Rosa hybrida) is a globally recognized ornamental plant whose growth and distribution are strongly limited by drought stress. The role of Mediator, a multiprotein complex crucial for RNA polymerase II-driven transcription, has been elucidated in drought stress responses in plants. However, its physiological function and regulatory mechanism in horticultural crop species remain elusive. RESULTS: In this study, we identified a Tail module subunit of Mediator, RhMED15a-like, in rose. Drought stress, as well as treatment with methyl jasmonate (MeJA) and abscisic acid (ABA), significantly suppressed the transcript level of RhMED15a-like. Overexpressing RhMED15a-like markedly bolstered the osmotic stress tolerance of Arabidopsis, as evidenced by increased germination rate, root length, and fresh weight. In contrast, the silencing of RhMED15a-like through virus induced gene silencing in rose resulted in elevated malondialdehyde accumulation, exacerbated leaf wilting, reduced survival rate, and downregulated expression of drought-responsive genes during drought stress. Additionally, using RNA-seq, we identified 972 differentially expressed genes (DEGs) between tobacco rattle virus (TRV)-RhMED15a-like plants and TRV controls. Gene Ontology (GO) analysis revealed that some DEGs were predominantly associated with terms related to the oxidative stress response, such as 'response to reactive oxygen species' and 'peroxisome'. Furthermore, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment highlighted pathways related to 'plant hormone signal transduction', in which the majority of DEGs in the jasmonate (JA) and ABA signalling pathways were induced in TRV-RhMED15a-like plants. CONCLUSION: Our findings underscore the pivotal role of the Mediator subunit RhMED15a-like in the ability of rose to withstand drought stress, probably by controlling the transcript levels of drought-responsive genes and signalling pathway elements of stress-related hormones, providing a solid foundation for future research into the molecular mechanisms underlying drought tolerance in rose.

Unveiling key mechanisms: Transcriptomic meta-analysis of diverse nanomaterial applications addressing biotic and abiotic stresses in Arabidopsis Thaliana.

The potential applications of nanomaterials in agriculture for alleviating diverse biotic and abiotic stresses have garnered significant attention. The reported mechanisms encompass promoting plant growth and development, alleviating oxidative stress, inducing defense responses, modulating plant-microbe interactions, and more. However, individual studies may not fully uncover the common pathways or distinguish the effects of different nanostructures. We examined Arabidopsis thaliana transcriptomes exposed to biotic, abiotic, and metal or carbon-based nanomaterials, utilizing 24 microarray chipsets and 17 RNA-seq sets. The results showed that: 1) from the perspective of different nanostructures, all metal nanomaterials relieved biotic/abiotic stresses via boosting metal homeostasis, particularly zinc and iron. Carbon nanomaterials induce hormone-related immune responses in the presence of both biotic and abiotic stressors. 2) Considering the distinct features of various nanostructures, metal nanomaterials displayed unique characteristics in seed priming for combating abiotic stresses. In contrast, carbon nanomaterials exhibited attractive features in alleviating water deprivation and acting as signaling amplifiers during biotic stress. 3) For shared pathway analysis, response to hypoxia emerges as the predominant and widely shared regulatory mechanism governing diverse stress responses, including those induced by nanomaterials. By deciphering shared and specific pathways and responses, this research opens new avenues for precision nano-agriculture, offering innovative strategies to optimize plant resilience, improve stress management, and advance sustainable crop production practices.

Functional analysis of a wheat class III peroxidase gene, TaPer12-3A, in seed dormancy and germination.

BACKGROUND: Class III peroxidases (PODs) perform crucial functions in various developmental processes and responses to biotic and abiotic stresses. However, their roles in wheat seed dormancy (SD) and germination remain elusive. RESULTS: Here, we identified a wheat class III POD gene, named TaPer12-3A, based on transcriptome data and expression analysis. TaPer12-3A showed decreasing and increasing expression trends with SD acquisition and release, respectively. It was highly expressed in wheat seeds and localized in the endoplasmic reticulum and cytoplasm. Germination tests were performed using the transgenic Arabidopsis and rice lines as well as wheat mutant mutagenized with ethyl methane sulfonate (EMS) in Jing 411 (J411) background. These results indicated that TaPer12-3A negatively regulated SD and positively mediated germination. Further studies showed that TaPer12-3A maintained H2O2 homeostasis by scavenging excess H2O2 and participated in the biosynthesis and catabolism pathways of gibberellic acid and abscisic acid to regulate SD and germination. CONCLUSION: These findings not only provide new insights for future functional analysis of TaPer12-3A in regulating wheat SD and germination but also provide a target gene for breeding wheat varieties with high pre-harvest sprouting resistance by gene editing technology.

Complex control of seed germination timing by ERF50 involves RGL2 antagonism and negative feedback regulation of DOG1.

Seed dormancy governs germination timing, with both evolutionary and applied consequences. Despite extensive studies on the hormonal and genetic control of these processes, molecular mechanisms directly linking dormancy and germination remain poorly understood. By screening a collection of lines overexpressing Arabidopsis transcription factors, we identified ERF50 as a key gene to control dormancy and germination. To study its regulation, we measured seed-related physiological parameters in loss-of-function mutants and carried out transactivation, protein interaction and ChIP-PCR analyses. We found direct ERF50-mediated repression of DOG1 and activation of EXPA2 transcription, which results in enhanced seed germination. Although ERF50 expression is increased by DOG1 in dormant seeds, ERF50 germination-promoting activity is blocked by RGL2. The physiological, genetic and molecular evidence gathered here supports that ERF50 controls germination timing by regulating DOG1 levels to leverage its role as enhancer of seed germination, via RGL2 antagonism on EXPA2 expression. Our results highlight the central role of ERF50 as a feedback regulator to couple and fine-tune seed dormancy and germination.

Involvement of GLR-mediated nitric oxide effects on ROS metabolism in Arabidopsis plants under salt stress.

Plant glutamate receptor-like channels (GLRs) play important roles in plant development, immune response, defense signaling and Nitric oxide (NO) production. However, their involvement in abiotic stress responses, particularly in regulating Reactive Oxygen Species (ROS), is not well understood. This study aimed to investigate GLR-mediated NO production on ROS regulation in salt-stressed cells. To achieve this, Arabidopsis thaliana Columbia (Col-0) were treated with NaCl, glutamate antagonists [(DNQX (6,7-dinitroquinoxaline-2,3-dione and AP-5(D-2-amino-5-phosphono pentanoic acid)], and NO scavenger [cPTIO (2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt)]. Salt-stressed plants in combination with DNQX and AP-5 have exhibited higher increase in lipid peroxidation (TBARS), hydrogen peroxide (H2O2) and superoxide radical (O-2) contents as compared to solely NaCl-treated plants. Furthermore, NO and total glutathione contents, and S-nitrosoglutathione reductase (GSNOR) activity decreased with these treatments. AP-5 and DNQX increased the activities of NADPH oxidase (NOX), catalase (CAT), peroxidase (POX), cell wall peroxidase (CWPOX) in salt-stressed Arabidopsis leaves. However, their activities (except NOX) were significantly inhibited by cPTIO. Conversely, the combination of NaCl and GLR antagonists, NO scavenger decreased the activities of ascorbate peroxidase (APX), superoxide dismutase (SOD), glutathione reductase (GR), dehydroascorbate reductase (DHAR) and monodehydroascorbate reductase (MDHAR) resulting in elevated GSSG levels, a low GSH/GSSG ratio, impaired ROS scavenging, excessive ROS accumulation and cell membrane damage. The findings of this study provide evidence that GLR-mediated NO plays a crucial role in improvement of the tolerance of Arabidopsis plants to salt-induced oxidative stress. It helps to maintain cellular redox homeostasis by reducing ROS accumulation and increasing the activity of SOD, GSNOR, and the ASC-GSH cycle enzymes.

A novel lectin receptor kinase gene, AtG-LecRK-I.2, enhances bacterial pathogen resistance through regulation of stomatal immunity in Arabidopsis.

The S-locus lectin receptor kinases (G-LecRKs) have been suggested as receptors for microbe/damage-associated molecular patterns (MAMPs/DAMPs) and to be involved in the pathogen defense responses, but the functions of most G-LecRKs in biotic stress response have not been characterized. Here, we identified a member of this family, G-LecRK-I.2, that positively regulates flg22- and Pseudomonas syringae pv. tomato (Pst) DC3000-induced stomatal closure. G-LecRK-I.2 was rapidly phosphorylated under flg22 treatment and could interact with the FLS2/BAK1 complex. Two T-DNA insertion lines, glecrk-i.2-1 and glecrk-i.2-2, had lower levels of reactive oxygen species (ROS) and nitric oxide (NO) production in guard cells, as compared with the wild-type Col-0, under Pst DC3000 infection. Also, the immunity marker genes CBP60g and PR1 were induced at lower levels under Pst DC3000 hrcC- infection in glecrk-i.2-1 and glecrk-i.2-2. The GUS reporter system also revealed that G-LecRK-I.2 was expressed only in guard cells. We also found that G-LecRK-I.2 could interact H+-ATPase AHA1 to regulate H+-ATPase activity in the guard cells. Taken together, our results show that G-LecRK-I.2 plays an important role in regulating stomatal closure under flg22 and Pst DC3000 treatments and in ROS and NO signaling specifically in guard cells.

Hardware Development for Plant Cultivation Allowing In Situ Fluorescence Analysis of Calcium Fluxes in Plant Roots Under Microgravity and Ground-Control Conditions.

Maintaining an optimal leaf and stem orientation to yield a maximum photosynthetic output is accomplished by terrestrial plants using sophisticated mechanisms to balance their orientation relative to the Earth's gravity vector and the direction of sunlight. Knowledge of the signal transduction chains of both gravity and light perception and how they influence each other is essential for understanding plant development on Earth and plant cultivation in space environments. However, in situ analyses of cellular signal transduction processes in weightlessness, such as live cell imaging of signaling molecules using confocal fluorescence microscopy, require an adapted experimental setup that meets the special requirements of a microgravity environment. In addition, investigations under prolonged microgravity conditions require extensive resources, are rarely accessible, and do not allow for immediate sample preparation for the actual microscopic analysis. Therefore, supply concepts are needed that ensure both the viability of the contained plants over a longer period of time and an unhindered microscopic analysis in microgravity. Here, we present a customized supply unit specifically designed to study gravity-induced Ca2+ mobilization in roots of Arabidopsis thaliana. The unit can be employed for ground-based experiments, in parabolic flights, on sounding rockets, and probably also aboard the International Space Station.

Dynamics and interplay of photosynthetic regulatory processes depend on the amplitudes of oscillating light.

Plants have evolved multiple regulatory mechanisms to cope with natural light fluctuations. The interplay between these mechanisms leads presumably to the resilience of plants in diverse light patterns. We investigated the energy-dependent nonphotochemical quenching (qE) and cyclic electron transports (CET) in light that oscillated with a 60-s period with three different amplitudes. The photosystem I (PSI) and photosystem II (PSII) function-related quantum yields and redox changes of plastocyanin and ferredoxin were measured in Arabidopsis thaliana wild types and mutants with partial defects in qE or CET. The decrease in quantum yield of qE due to the lack of either PsbS- or violaxanthin de-epoxidase was compensated by an increase in the quantum yield of the constitutive nonphotochemical quenching. The mutant lacking NAD(P)H dehydrogenase (NDH)-like-dependent CET had a transient significant PSI acceptor side limitation during the light rising phase under high amplitude of light oscillations. The mutant lacking PGR5/PGRL1-CET restricted electron flows and failed to induce effective photosynthesis control, regardless of oscillation amplitudes. This suggests that PGR5/PGRL1-CET is important for the regulation of PSI function in various amplitudes of light oscillation, while NDH-like-CET acts' as a safety valve under fluctuating light with high amplitude. The results also bespeak interplays among multiple photosynthetic regulatory mechanisms.

Strong prevalence of light regime-specific QTL in Arabidopsis detected using automated high-throughput phenotyping in fluctuating or constant light.

Plants have evolved and adapted under dynamic environmental conditions, particularly to fluctuating light, but plant research has often focused on constant growth conditions. To quantitatively asses the adaptation to fluctuating light, a panel of 384 natural Arabidopsis thaliana accessions was analyzed in two parallel independent experiments under fluctuating and constant light conditions in an automated high-throughput phenotyping system upgraded with supplemental LEDs. While the integrated daily photosynthetically active radiation was the same under both light regimes, plants in fluctuating light conditions accumulated significantly less biomass and had lower leaf area during their measured vegetative growth than plants in constant light. A total of 282 image-derived architectural and/or color-related traits at six common time points, and 77 photosynthesis-related traits from one common time point were used to assess their associations with genome-wide natural variation for both light regimes. Out of the 3000 significant marker-trait associations (MTAs) detected, only 183 (6.1%) were common for fluctuating and constant light conditions. The prevalence of light regime-specific QTL indicates a complex adaptation. Genes in linkage disequilibrium with fluctuating light-specific MTAs with an adjusted repeatability value >0.5 were filtered for gene ontology terms containing "photo" or "light", yielding 15 selected candidates. The candidate genes are involved in photoprotection, PSII maintenance and repair, maintenance of linear electron flow, photorespiration, phytochrome signaling, and cell wall expansion, providing a promising starting point for further investigations into the response of Arabidopsis thaliana to fluctuating light conditions.