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Significantly regulated genes in WT, ahk2 ahk3 and cca1 lhy after photoperiod stress. (A) Experimental setup used in this study. 5-week-old short-day (SD)-grown plants were exposed to a prolonged light period (PLP) of 32 h followed by a normal SD night. White, light period; black, dark period. Arrows indicate sampling time points for RNA analysis. (B–D) Venn diagrams showing the overlap of DEGs at different time points for WT (B), ahk2 ahk3 (C) and cca1 lhy (D). Numbers in brackets indicate the total number of DEGs (| fold-change| = 2; Bonferroni-corrected p-value ≤ 0.05) in PLP-treated plants compared with control plants at the different time points. (E–G) Top 5 GO enrichment terms for time point 4 and 6 h for WT (E), ahk2 ahk3 (F) and cca1 lhy (G). A list of top-5 GO enrichment terms pro timepoint can be found in Supplementary Table 2. An overview of the gene regulation for the comparisons between PLP and control treatments for WT, ahk2 ahk3 and cca1 lhy is shown for all time points in Supplementary Data 2. A core-set of photoperiod stress-responsive genes is listed in Supplementary Table 3 and the top 20 most highly regulated genes at each time point are listed in Supplementary Tables 6–11.
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Plants are exposed to regular diurnal rhythms of light and dark. Changes in the photoperiod by the prolongation of the light period cause photoperiod stress in short day-adapted Arabidopsis thaliana. Here, we report on the transcriptional response to photoperiod stress of wild-type A. thaliana and photoperiod stress-sensitive cytokinin signaling an...
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Main conclusion
The simultaneous perception of endogenous and exogenous danger signals potentiates PAMP-triggered immunity in tomato and other downstream defence responses depending on the origin of the signal.
Abstract Plant cells perceive a pathogen invasion by recognising endogenous or exogenous extracellular signals such as Damage-Associated Mo...
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... Research conducted by Nitschke et al. in 2016 [10] and 2017 [11] unveiled that an abrupt extension of the photoperiod induces a novel form of abiotic stress known as photoperiod stress. This stress condition leads to nightly accumulation of reactive oxygen species (ROS) that triggers a stress response akin to a pathogen infection, as demonstrated by Abuelsoud et al. in 2020 [12] and Cortleven et al. in 2022 [13]. Progress in analyzing bacterial genome sequences further revealed that non-photosynthetic as well as photosynthetic prokaryotes are capable of sensing and responding to multiple light colors [14]. ...
With the increasing availability of LEDs, researchers in photobiology have easier access to customized light sources. However, the abundance of different light sources poses new challenges for the correct characterization of existing light conditions. The photobiological effect of a light source depends mainly on the number of photons involved and the spectral composition. However, light sources are mainly described by parameters such as radiant flux, dominant or peak wavelength, and correlated color temperature (CCT). Therefore, in this work, chromatic and white light sources were measured for their spectral composition, various characterization parameters were determined, and the resulting photon flux densities were calculated, focusing on dominant versus peak wavelength for chromatic LEDs and the CCT for white LEDs and fluorescent tubes. The use of the dominant wavelength is inappropriate as it is partly outside the actual spectral range. It was also shown that white light sources with the same CCT have significantly different spectral compositions and, therefore, may have different photobiological effects. The results of this work should serve as a basis for life scientists to better compare light sources, to correctly interpret existing parameters, and to describe light conditions in a standardized and comparable way.
... The circadian rhythm is coordinated with environmental signals to maintain plant fitness and survival via various hormone pathways and contributes to regulation of seed germination, leaf growth, photosynthesis and flowering [38][39][40]. The circadian rhythm regulates abiotic stress responses in a wide range of plants, including Arabidopsis, soybean, barley and rice [41][42][43][44][45]. Key circadian clock regulators, CCA1, LHY, CHE, TIC and TOC1, regulate stress responses via crosstalk with salicylic acid, jasmonic acid and ethylene signalling pathways [46,47]. TIMING OF CAB EXPRESSION 1 (TOC1) can be induced by ABA treatment and then contribute to ABA signalling induction [48]. ...
The environment is seldom optimal for plant growth and changes in abiotic and biotic signals, including temperature, water availability, radiation and pests, induce plant responses to optimise survival. The New Zealand native plant species and close relative to Arabidopsis thaliana, Pachycladon cheesemanii, grows under environmental conditions that are unsustainable for many plant species. Here, we compare the responses of both species to different stressors (low temperature, salt and UV-B radiation) to help understand how P. cheesemanii can grow in such harsh environments. The stress transcriptomes were determined and comparative transcriptome and network analyses discovered similar and unique responses within species, and between the two plant species. A number of widely studied plant stress processes were highly conserved in A. thaliana and P. cheesemanii. However, in response to cold stress, Gene Ontology terms related to glycosinolate metabolism were only enriched in P. cheesemanii. Salt stress was associated with alteration of the cuticle and proline biosynthesis in A. thaliana and P. cheesemanii, respectively. Anthocyanin production may be a more important strategy to contribute to the UV-B radiation tolerance in P. cheesemanii. These results allowed us to define broad stress response pathways in A. thaliana and P. cheesemanii and suggested that regulation of glycosinolate, proline and anthocyanin metabolism are strategies that help mitigate environmental stress.
... The circadian rhythm is coordinated with environmental signals to maintain plant fitness and survival via various hormone pathways and contribute to regulation of seed germination, leaf growth, photosynthesis and flowering [38][39][40]. The circadian rhythm regulates abiotic stress responses in a wide range of plant, including Arabidopsis, soybean, barley and rice [41][42][43][44][45]. Key circadian clock regulators, CCA1, LHY, CHE, TIC and TOC1, regulate stress responses via crosstalk with salicylic acid, jasmonic acid and ethylene signalling pathways [46,47]. TIMING OF CAB EXPRESSION 1 (TOC1) can be induced by ABA treatment, and then contribute to ABA signalling induction [48]. ...
The environment is seldom optimal for plant growth and changes in abiotic and biotic signals, including temperature, water availability, radiation and pests, induce plant responses to optimise survival. The New Zealand native plant species and close relative to Arabidopsis thaliana, Pachycladon cheesemanii grows under environmental conditions that are unsustainable for many plant species. Here we compare the responses of both plant species to different stressors (low temperature, salt and UV-B radiation) to help understand how P. cheesemanii can grow in such harsh environments. The stress transcriptomes were then determined and comparative transcriptome and network analyses discovered similar and unique responses within species between different stresses, and between the two plant species. A number of widely studied plant stress processes were highly conserved in A. thaliana and P. cheesemanii. However, in response to cold stress, Gene Ontology terms related to glycosinolate metabolism were only enriched in P. cheesemanii. Salt stress was associated with alteration of the cuticle and proline biosynthesis in A. thaliana and P. cheesemanii, respectively. Anthocyanin production may be a strategy to cope with UV-B radiation stress in P. cheesemanii only. These results allowed us to construct broad stress response pathways in A. thaliana and P. cheesemanii and identify possible novel plant strategies that help mitigate environmental stress.
... In agreement with our findings, a recent report revealed that SArelated responses are primed by photoperiodic stress 33 . Considering that SA can antagonize ABA responses, we investigated whether SA is necessary for light-mediated prevention of water-soaked lesions. ...
... However, our results showing that it affects aROS production and SArelated responses, but not early PTI responses, suggest that constant light affects specific modules in plant immunity. At the same time, our results are consistent with a recent study showing that, under photoperiodic stress, the Arabidopsis transcriptional signature resembles that of a response to pathogens 33 . Notably, SA signatures increased in plants kept under constant light and were reduced in dark-grown plants. ...
Many plant pathogens induce water-soaked lesions in infected tissues. In the case of Pseudomonas syringae (Pst), water-soaking effectors stimulate abscisic acid (ABA) production and signaling, resulting in stomatal closure. This reduces transpiration, increases water accumulation, and induces an apoplastic microenvironment favorable for bacterial growth. Stomata are sensitive to environmental conditions, including light. Here, we show that a period of darkness is required for water-soaking, and that a constant light regime abrogates stomatal closure by Pst. We find that constant light induces resistance to Pst, and that this effect requires salicylic acid (SA). Constant light did not alter effector-induced accumulation of ABA, but induced greater SA production, promoting stomatal opening despite the presence of ABA. Furthermore, application of a SA analog was sufficient to prevent pathogen-induced stomatal closure and water-soaking. Our results suggest potential approaches for interfering with a common virulence strategy, as well as providing a physiological mechanism by which SA functions in defense against pathogens.
... To investigate the possible involvement of auxin in the photoperiod stress response, we first analyzed the transcript abundance of genes involved in auxin synthesis, metabolism and signaling after photoperiod stress. The changes of transcript abundance were compared in leaves of stressed (PLP) and non-stressed (control) wild-type and ahk2,3 plants 0, 4, 6 and 12 h after PLP treatment using data from RNA-seq analysis (Cortleven et al. [33]; Figures 1 and 2; Supplemental Tables S1 and S2). The changes in transcript abundance in response to photoperiod stress were confirmed for several genes by qRT-PCR (Supplemental Figure S1). ...
... Table S1). Data were extracted from [33]. Table S2). ...
... Table S2). Data were extracted from [33]. ...
Fluctuating environmental conditions trigger adaptive responses in plants, which are regulated by phytohormones. During photoperiod stress caused by a prolongation of the light period, cytokinin (CK) has a protective function. Auxin often acts as an antagonist of CK in developmental processes and stress responses. Here, we investigated the regulation of the photoperiod stress response in Arabidopsis thaliana by auxin and its interaction with CK. Transcriptome analysis revealed an altered transcript abundance of numerous auxin metabolism and signaling genes after photo-period stress treatment. The changes appeared earlier and were stronger in the photoperiod-stress-sensitive CK receptor mutant arabidopsis histidine kinase 2 (ahk2),3 compared to wild-type plants. The concentrations of indole-3-acetic acid (IAA), IAA-Glc and IAA-Asp increased in both genotypes, but the increases were more pronounced in ahk2,3. Genetic analysis revealed that the gain-of-function YUCCA 1 (YUC1) mutant, yuc1D, displayed an increased photoperiod stress sensitivity. In contrast , a loss of the auxin receptors TRANSPORT-INHIBITOR-RESISTANT 1 (TIR1), AUXIN SIG-NALING F-BOX 2 (AFB2) and AFB3 in wild-type and ahk2,3 background caused a reduced photo-period stress response. Overall, this study revealed that auxin promotes response to photoperiod stress antagonizing the protective CK
Chloroplasts are essential centers of signal integration and transduction in plants. They are involved in the biosynthesis of primary and specialized metabolites, including salicylic acid (SA), a key defense phytohormone synthesized via the conserved chorismate biosynthetic pathway. However, the identity of the signal(s) that ultimately triggers SA induction in chloroplasts upon perception of a biotic threat has remained elusive. Here, we provide evidence of a functional link between chloroplast-derived reactive oxygen species (cROS) and SA production. We observe that inhibiting ROS bursts generated from photosystem II during plant immune activation completely abrogates the induction of SA synthesis in response to immunity-inducing signals, without affecting SA-independent immune responses. Indeed, time course analyses show that the induction of SA marker genes parallels that of cROS production during an immune response. Consistent with this, preventing cROS induction is sufficient to nullify the immune protection normally conferred by activating immunity prior to an infection. Analyses of transcriptomes and photosynthetic efficiency show that two conserved effectors from the phytopathogen Pseudomonas syringae , HopM1 and AvrE1, redundantly disrupt photosynthesis and cROS bursts. These effects reduce SA accumulation and are mediated via the impact of HopM1 and AvrE1 in inducting host abscisic acid signaling. Our results suggest that a change in chloroplastic redox homeostasis induced by biotic stressors acts as an initiator of plant immunity through the production of SA, and that this response is targeted by conserved pathogen effector proteins.
24 h cold exposure (4°C) is sufficient to reduce pathogen susceptibility in Arabidopsis thaliana against the virulent Pseudomonas syringae pv. tomato (Pst) strain even when the infection occurs five days later. This priming effect is independent of the immune regulator Enhanced Disease Susceptibility 1 (EDS1) and can be observed in the immune-compromised eds1–2 null mutant. In contrast, cold priming-reduced Pst susceptibility is strongly impaired in knock-out lines of the stromal and thylakoid ascorbate peroxidases (sAPX/tAPX) highlighting their relevance for abiotic stress-related increased immune resilience. Here, we extended our analysis by generating an eds1 sapx double mutant. eds1 sapx showed eds1-like resistance and susceptibility phenotypes against Pst strains containing the effectors avrRPM1 and avrRPS4. In comparison to eds1–2, susceptibility against the wildtype Pst strain was constitutively enhanced in eds1 sapx. Although a prior cold priming exposure resulted in reduced Pst titers in eds1–2, it did not alter Pst resistance in eds1 sapx. This demonstrates that the genetic sAPX requirement for cold priming of basal plant immunity applies also to an eds1 null mutant background.
