Biology subjects

Brosche, M.

Publications and source records attributed to Brosche, M..

12 recordsLinked to original sources

bioRxiv2025

The EGY1-SGR1 module controls chloroplast development and senescence by modulating photosynthetic functions

The chloroplast plays essential roles not only in production of biochemical energy and metabolism, but also in plant development, including senescence. We describe a mutant with an unusual progression of senescence and identify it as an allele of ethylene-dependent gravitropism-deficient and yellow-green 1 (egy1-5). EGY1 encodes a chloroplast-localized metalloprotease that regulates chlorophyll metabolism. The single egy1-5 mutant exhibits defects in various aspects of chloroplast function, including abnormal accumulation of photosynthetic complexes, defects in photosynthetic electron transfer chain and altered responses to the chemicals methyl viologen and lincomycin. Additionally, egy1 lacks guard cell chloroplasts. We performed a suppressor mutant screen in the egy1 background to identify new regulators of senescence and chloroplast development. We found two suppressors that restored green leaves and mapping revealed that both suppressors had mutations in STAY-GREEN 1 (SGR1). SGR1 encodes the Mg2+ dechelatase enzyme, which catalyses the first step in chlorophyll breakdown. Several defects in the egy1 mutant were either fully or partially suppressed in egy1 sgr1. This enabled the function of EGY1 to be isolated, independent of the pleiotropic effects of chlorophyll degradation. Our findings suggest that chlorophyll homeostasis regulates the overall development and function of the chloroplast as well as plant senescence. HighlightIdentifying new mutants with defects in chlorophyll metabolism and chloroplast development shows that proper chlorophyll homeostasis is necessary for maintaining functional chloroplasts.

plant biology↗

bioRxiv2025

Protection of photosynthesis by UVR8 and cryptochromes in Arabidopsis under blue and UV radiation

Photosynthesis in plants is negatively affected by high light intensity and UV radiation. The photoreceptors UV RESISTANCE LOCUS 8 (UVR8) and CRYPTOCHROMES (CRYs) mediate perception and acclimation of plants to UV-B/UV-A2 (290-340 nm) and UV-A1/blue light (350-500 nm), respectively. However, their roles in photoprotection of photosynthesis across different wavebands of the spectrum remain unclear. Using chlorophyll fluorescence and LED lighting we studied the roles of UVR8 and CRYs in maintaining photosynthetic capacity in Arabidopsis exposed to UV-B, UV-A1, and blue light. Analysis of quantum yield of Photosystem II, non-photochemical quenching, and LHCII phosphorylation demonstrated that CRYs preserve photosynthetic performance in plants exposed to UV-B, UV-A1, and blue light. UVR8 and CRYs exhibit partially redundant functions in maintaining photosynthetic activity under UV-B, UV-A1, and blue light, and in preventing photodamage under high UV-A1 irradiance. Impaired UVR8 and CRY signaling reduced epidermal flavonol accumulation in leaves, which further compromised photoprotection. These findings provide valuable insights into how UV and blue light perception contribute to photoprotection, with broad implications for plant performance both in natural and managed environments.

plant biology↗

bioRxiv2024

Water immunity overrides stomatal immunity in plant resistance to Pseudomonas syringae

Stomata play crucial roles in the multilayered defense system against pathogens. Upon pathogen perception, stomata close promptly, establishing the first line of defense known as stomatal immunity. The bacterial pathogen Pseudomonas syringae (Pst) exploits open stomata for entry, however, it can also induce stomatal closure at post-invasive stages to enhance apoplastic hydration. This creates a favorable environment for Pst proliferation, evident as water-soaked lesions on leaves. During the post-invasive stages of Pst infection, plants deploy a second layer of stomatal defense by reopening their stomata, a process termed water immunity. To evaluate the relative importance of stomatal versus water immunity, we utilized a diverse set of Arabidopsis (Arabidopsis thaliana) mutants with impaired stomatal function and monitored bacterial growth, stomatal behavior, and water-soaking capacity after Pst pv. tomato DC3000 infection. Most mutants with constitutively open stomata and disrupted stomatal closure were more resistant against Pst than wild-type plants. Also, while some stomatal mutants displayed similar stomatal behavior at the initial steps of defense, their disease outcomes were the opposite, suggesting that stomatal immunity is not the determining factor in disease resistance. Instead, we discovered that the water-soaking capacity, associated with stomatal status at later stages of infection, i.e., water immunity, dictates the disease outcome. Our results show that water immunity can override the lack of stomatal immunity in plant resistance to Pst. We also address previous discrepancies in literature showing contradicting results for pathogen growth on stomatal mutants, highlighting the challenges in dissecting stomatal effects on plant resistance.

plant biology↗

bioRxiv2022

BOS1 is a positive regulator of wounding induced cell death and plant susceptibility to Botrytis

Programmed cell death (PCD) is required for many aspects of plant biology, including stress responses, immunity, and plant development including root and flower development. Our understanding of PCD regulation is incomplete, especially concerning regulators involved in multiple divergent processes. The botrytis-suscetible1 (bos1) mutant is one of the genotypes most susceptible to Botrytis cinerea (Botrytis) and has revealed the role of BOS1 in cell death propagation during plant responses to wounding. The bos1-1 allele harbours a T-DNA located in the 5UTR upstream from the start codon that results in elevated BOS1 transcript levels. Here, we resequenced the bos1-1 genome and found a MAS promoter at the ends of the T-DNAs. Expression of the BOS1 gene under control of the MAS promoter conferred the characteristic bos1-1 Botrytis- sensitivity and wounding phenotypes in wildtype plants. We used Crispr-Cas9 to create new bos1 alleles that disrupt exons. These lines lacked the typical bos1-1 wounding and Botrytis phenotypes, but exhibited reduced fertility, as previously observed in other bos1 T-DNA alleles. With multiple overexpression lines of BOS1, we demonstrate that BOS1 is involved in regulation of cell death propagation in a dosage dependent manner. Our data support that bos1-1 is a gain-of-function mutant and that BOS1 acts as a positive regulator of wounding and Botrytis-induced PCD. Taken together these finding suggest that BOS1 function in both fertility and Botrytis response could be unified under cell death control.

plant biology↗

bioRxiv2021

Dissecting the subtropical adaptation traits and cuticle synthesis pathways via the genome of the subtropical blueberry Vaccinium darrowii

Vaccinium darrowii is a subtropical wild blueberry species, which was used to breed economically important southern highbush cultivars. The adaptation traits of V. darrowii to subtropical climate would provide valuable information for breeding blueberry and perhaps other plants, especially against the background of global warming. Here, we assembled the V. darrowii genome into 12 pseudochoromosomes using Oxford Nanopore long reads complemented with Hi-C scaffolding technologies, and predicted 41 815 genes using RNAseq evidence. Syntenic analysis across three Vaccinium species revealed a highly conserved genome structure, with the highest collinearity between V. darrowii and V. corymbosum. This conserved genome structure may explain the high fertilization during crossbreeding between V. darrowii and other blueberry cultivars. Gene expansion and tandem duplication analysis indicated possible roles of defense and flowering associated genes in adaptation of V. darrowii to the subtropics. The possible SOC1 genes in V. darrowii were identified with phylogeny and expression analysis. Blueberries are covered in a thick cuticle layer and contain anthocyanins, which confer their powdery blue color. Using RNA-sequencing, the cuticle biosynthesis pathways of Vaccinium species were delineated here in V. darrowii. This result could serve as a reference for breeding berries with customer-desired colors. The V. darrowii reference genome, together with the unique traits of this species, including diploid genome, short vegetative phase, and high compatibility in hybridization with other blueberries, make V. darrowii a potential research model for blueberry species.

plant biology↗

bioRxiv2020

The photoreceptor UVR8 mediates the perception of both UV-B and UV-A wavelengths up to 350 nm of sunlight with responsivity moderated by cryptochromes

The photoreceptors UV RESISTANCE LOCUS 8 (UVR8) and CRYPTOCHROMES 1 and 2 (CRYs) play major roles in the perception of UV-B (280-315 nm) and UV-A/blue radiation (315-500 nm), respectively. However, it is poorly understood how they function in sunlight. The roles of UVR8 and CRYs were assessed in a factorial experiment with Arabidopsis thaliana wild-type and photoreceptor mutants exposed to sunlight for 6 h or 12 h under five types of filters with cut-offs in UV and blue-light regions. Transcriptome-wide responses triggered by UV-B and UV-A wavelengths shorter than 350 nm (UV-Asw) required UVR8 whereas those induced by blue and UV-A wavelengths longer than 350 nm (UV-Alw) required CRYs. UVR8 modulated gene expression in response to blue light while lack of CRYs drastically enhanced gene expression in response to UV-B and UV-Asw. These results agree with our estimates of photons absorbed by these photoreceptors in sunlight and with in vitro monomerization of UVR8 by wavelengths up to 335 nm. Motif enrichment analysis predicted complex signaling downstream of UVR8 and CRYs. Our results highlight that it is important to use UV waveband definitions specific to plants photomorphogenesis as is routinely done in the visible region.

plant biology↗

bioRxiv2019

Evolutionary conservation and multilevel post-translational control of S-adenosyl-homocysteine-Hydrolase in land plants

Trans-methylation reactions are intrinsic to cellular metabolism in all living organisms. In land plants, a range of substrate-specific methyltransferases catalyze the methylation of DNA, RNA, proteins, cell wall components and numerous species-specific metabolites, thereby providing means for growth and acclimation in various terrestrial habitats. Trans-methylation reactions consume vast amounts of S-adenosyl-L-methionine (SAM) as a methyl donor in several cellular compartments. The inhibitory reaction by-product, S-adenosyl-L-homocysteine (SAH), is continuously removed by SAH hydrolase (SAHH) activity, and in doing so essentially maintains trans-methylation reactions in all living cells. Here we report on the evolutionary conservation and multilevel post-translational control of SAHH in land plants. We find that SAHH forms oligomeric protein complexes in phylogenetically divergent land plants, and provide evidence that the predominant enzyme is a tetramer. By analyzing light-stress-induced adjustments occurring on SAHH in Arabidopsis thaliana and Physcomitrella patens, we demonstrate that both angiosperms and bryophytes undergo regulatory adjustments in the levels of protein complex formation and post-translational modification of this metabolically central enzyme. Collectively, these data suggest that plant adaptation to terrestrial environments involved evolution of regulatory mechanisms that adjust the trans-methylation machinery in response to environmental cues.

plant biology↗

bioRxiv2019

Automated Processing and Statistical Analysis of NMR spectra obtained from Arabidopsis thaliana Extracts

To cope with vast amounts of data produced by metabolomic and mixture analysis using NMR, the employed analysis techniques and tools are very important. In this paper, we demonstrate quantitative 1H and 2D-JRES NMR analysis of Arabidopsis thaliana extracts utilizing our ImatraNMR and SimpeleNMR software to automate the processing the spectra, extracting data, and perform statistical analysis of the results. Metabolomes of four different strains of Arabidopsis thaliana are analyzed under control conditions and during acute ozone exposure. Key differences are identified between accessions Col-0 and Cvi-0 (epithionitriles, iberin nitrile) and ozone damage associated metabolite(s) can be identified. Sample stability is also addressed.

biochemistry↗

bioRxiv2019

The role of strigolactones in regulation of stomatal conductance and plant-pathogen interactions in Arabidopsis thaliana

Strigolactones are a group of phytohormones that control shoot branching in Arabidopsis thaliana. However, in recent years they have been shown to affect many other plant processes. We previously showed that the strigolactone perception mutant more axillary branches 2 (max2) has increased susceptibility to plant pathogenic bacteria as a result of more open stomata as well as alterations in hormonal signalling. Here we show that both, strigolactone biosynthesis- (max3 and max4), and perception mutants (max2 and dwarf14) are significantly more sensitive to Pseudomonas syringae DC3000. Moreover, in response to P. syringae infection, high levels of SA accumulated in max2 and this mutant was ozone sensitive. To search for the mechanisms that could explain pathogen- and ozone sensitivity we performed gene expression analysis and several different assays that explore the function of guard cells and regulation of guard cell signalling.\n\nTreatments with GR24 (a strigolactone analogue) resulted in very modest changes in defence-related gene expression. In contrast, guard cell function was clearly impaired in max2 and depending on the assay used, also in max3, max4 and d14 mutants. Moreover, stomatal responses to stimuli that cause stomatal closure in wild-type plants (darkness, high CO2 and ABA) were analysed in the strigolactone mutants. In darkness both strigolactone biosynthesis and perception mutants showed reduced stomatal closure, whereas the response to high CO2 was impaired only in max2 and d14. The response to ABA was not impaired in any of the mutants. To position the role of MAX2 in the guard cell signalling network, max2 was crossed with mutants defective in ABA biosynthesis (aba2), in guard cell ABA signalling (ost1) and a scaffold protein required for proper ion channel activity (ghr1). The stomatal conductance of double mutants was consistently higher than the corresponding single mutants, suggesting that MAX2 acts in a signalling pathway that functions in parallel to the well characterized guard cell ABA signalling pathway. We propose that the impaired defence responses of max2 is related to more open stomata that allows increased entry of bacteria or air pollutants like ozone. Furthermore, as MAX2 appears to act in a specific branch of guard cell signalling (related to CO2 signalling), this protein could be one of the elusive components that allow guard cells to distinguish between different environmental conditions.

plant biology↗

bioRxiv2018

Methyl viologen can affect mitochondrial function in Arabidopsis.

Reactive oxygen species (ROS) are key signalling intermediates in plant metabolism, defence, and stress adaptation. The chloroplast and mitochondria are centres of metabolic control and ROS production, which coordinate stress responses in other cell compartments. The herbicide and experimental tool, methyl viologen (MV) induces ROS generation in the chloroplast under illumination, but is also toxic in non-photosynthetic organisms. We used MV to probe plant ROS signalling in compartments other than the chloroplast. Taking a genetic approach in Arabidopsis thaliana, we used natural variation, QTL mapping, and mutant studies with MV in the light, but also under dark conditions, when the chloroplast electron transport is inactive. These studies revealed a light-independent MV-induced ROS-signalling pathway, suggesting mitochondrial involvement. Mitochondrial Mn SUPEROXIDE DISMUTASE was required for ROS-tolerance and the effect of MV was enhanced by exogenous sugar, providing further evidence for the role of mitochondria. Mutant and hormone feeding assays revealed roles for stress hormones in organellar ROS-responses. The radical-induced cell death1 mutant, which is tolerant to MV-induced ROS and exhibits altered mitochondrial signalling, was used to probe interactions between organelles. Our studies implicate mitochondria in the response to ROS induced by MV.

plant biology↗

bioRxiv2018

Complexity of ABA signaling for stomatal development and aperture regulation

Stomata, small pores on the surfaces of leaves formed by a pair of guard cells, adapt rapidly to changes in the environment by adjusting the aperture width. As a long term response, the number of stomata is regulated during stomatal development. The hormone abscisic acid (ABA) regulates both processes. In ABA mediated guard cell signaling the protein kinase OPEN STOMATA1 (OST1) has a central role, as stomatal closure in the ost1 mutant is impaired in response to ABA and to different environmental stimuli. We aimed to dissect the contribution of different ABA-related regulatory mechanisms in determining stomatal conductance, a combination of stomatal density and aperture width, and crossed the ost1 mutant with mutants that either decreased (aba3) or increased (cyp707a1/a3) the concentration of ABA in plants. The double mutant ost1 aba3 had higher stomatal conductance than either parent due to a combination of increased stomatal aperture width and higher stomatal density. In the triple mutant ost1 cyp707a1/a3 stomatal conductance was significantly lower compared to ost1-3 due to lower stomatal density. Further characterization of the single, double and triple mutants showed that responses to treatments that lead to stomatal closure were impaired in ost1 as well as ost1 aba3 and ost1 cyp707a1/a3 mutants, supporting a critical role for OST1 in stomatal aperture regulation. Based on our results, we suggest that there are two signaling pathways to regulate water flux from leaves i.e. stomatal conductance: an ABA-dependent pathway that determines stomatal density independent of OST1; and an OST1-dependent pathway that regulates rapid changes in stomatal aperture.

plant biology↗

bioRxiv2018

RCD1 Coordinates Chloroplastic and Mitochondrial Electron Transfer through Interaction with ANAC Transcription Factors

Signaling from chloroplasts and mitochondria, both dependent on reactive oxygen species (ROS), merge at the nuclear protein RADICAL-INDUCED CELL DEATH1 (RCD1). ROS produced in the chloroplasts affect the abundance, thiol redox state and oligomerization of RCD1. RCD1 directly interacts in vivo with ANAC013 and ANAC017 transcription factors, which are the mediators of the ROS-related mitochondrial complex III retrograde signa and suppresses activity of ANAC013 and ANAC017. Inactivation of RCD1 leads to increased expression of ANAC013 and ANAC017-regulated genes belonging to the mitochondrial dysfunction stimulon (MDS), including genes for mitochondrial alternative oxidases (AOXs). Accumulating AOXs and other MDS gene products alter electron transfer pathways in the chloroplasts, leading to diminished production of chloroplastic ROS and increased protection of photosynthetic apparatus from ROS damage. RCD1-dependent regulation affects chloroplastic and mitochondrial retrograde signaling including chloroplast signaling by 3-phosphoadenosine 5-phosphate (PAP). Sensitivity of RCD1 to organellar ROS provides feedback control of nuclear gene expression.

plant biology↗