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Publikation

Picchianti, L.; Sanchez de Medina Hernandez, V.; Zhan, N.; Irwin, N. A.; Groh, R.; Stephani, M.; Hornegger, H.; Beveridge, R.; Sawa‐Makarska, J.; Lendl, T.; Grujic, N.; Naumann, C.; Martens, S.; Richards, T. A.; Clausen, T.; Ramundo, S.; Karagöz, G. E.; Dagdas, Y.; Shuffled ATG8 interacting motifs form an ancestral bridge between UFMylation and autophagy EMBO J. 42, e112053, (2023) DOI: 10.15252/embj.2022112053

UFMylation involves the covalent modification of substrate proteins with UFM1 (Ubiquitin-fold modifier 1) and is important for maintaining ER homeostasis. Stalled translation triggers the UFMylation of ER-bound ribosomes and activates C53-mediated autophagy to clear toxic polypeptides. C53 contains noncanonical shuffled ATG8-interacting motifs (sAIMs) that are essential for ATG8 interaction and autophagy initiation. However, the mechanistic basis of sAIM-mediated ATG8 interaction remains unknown. Here, we show that C53 and sAIMs are conserved across eukaryotes but secondarily lost in fungi and various algal lineages. Biochemical assays showed that the unicellular alga Chlamydomonas reinhardtii has a functional UFMylation pathway, refuting the assumption that UFMylation is linked to multicellularity. Comparative structural analyses revealed that both UFM1 and ATG8 bind sAIMs in C53, but in a distinct way. Conversion of sAIMs into canonical AIMs impaired binding of C53 to UFM1, while strengthening ATG8 binding. Increased ATG8 binding led to the autoactivation of the C53 pathway and sensitization of Arabidopsis thaliana to ER stress. Altogether, our findings reveal an ancestral role of sAIMs in UFMylation-dependent fine-tuning of C53-mediated autophagy activation.
Publikation

Tang, N.; Naumann, C.; Native protein purification of ferroxidase LPR1 from leaf extracts of a transgenic Arabidopsis thaliana line STAR Protocols 3, 101733, (2022) DOI: 10.1016/j.xpro.2022.101733

(LOW PHOSPHATE ROOT 1), a bacterial-type plant ferroxidase, is crucial for local root phosphate (Pi) sensing. Here, we present a detailed protocol for native (tag-free) protein purification of LPR1 from leaf extracts by differential ammonium sulfate precipitation, size exclusion, and cation exchange chromatography of a transgenic Arabidopsis thaliana line overexpressing LPR1. We outline steps for LPR1 purification tracking via immune blot analysis and ferroxidase activity assay. The protocol yields highly pure and active LPR1 protein for biochemical analysis. For complete details on the use and execution of this protocol, please refer to Naumann et al. (2022)
Publikation

Naumann, C.; Heisters, M.; Brandt, W.; Janitza, P.; Alfs, C.; Tang, N.; Toto Nienguesso, A.; Ziegler, J.; Imre, R.; Mechtler, K.; Dagdas, Y.; Hoehenwarter, W.; Sawers, G.; Quint, M.; Abel, S.; Bacterial-type ferroxidase tunes iron-dependent phosphate sensing during Arabidopsis root development Curr. Biol. 32, 2189-2205, (2022) DOI: 10.1016/j.cub.2022.04.005

Access to inorganic phosphate (Pi), a principal intermediate of energy and nucleotide metabolism, profoundly affects cellular activities and plant performance. In most soils, antagonistic Pi-metal interactions restrict Pi bioavailability, which guides local root development to maximize Pi interception. Growing root tips scout the essential but immobile mineral nutrient; however, the mechanisms monitoring external Pi sta-tus are unknown. Here, we show that Arabidopsis LOW PHOSPHATE ROOT 1 (LPR1), one key determinant of Fe-dependent Pi sensing in root meristems, encodes a novel ferroxidase of high substrate specificity and affinity (apparent KM ∼2 μmM Fe2+). LPR1 typifies an ancient, Fe-oxidizing multicopper protein family that evolved early upon bacterial land colonization. The ancestor of streptophyte algae and embryophytes (land plants) acquired LPR1-type ferroxidase from soil bacteria via horizontal gene transfer, a hypothesis supported by phylogenomics, homology modeling, and biochemistry. Our molecular and kinetic data on LPR1 regulation indicate that Pi-dependent Fe substrate availability determines LPR1 activity and function. Guided by the metabolic lifestyle of extant sister bacterial genera, we propose that Arabidopsis LPR1 monitors subtle concentration differentials of external Fe availability as a Pi-dependent cue to adjust root meristem maintenance via Fe redox signaling and cell wall modification. We further hypothesize that the acquisition of bacterial LPR1-type ferroxidase by embryophyte progenitors facilitated the evolution of local Pi sensing and acquisition during plant terrestrialization.
Publikation

Klionsky, D. J.; Abdel-Aziz, A. K.; Abdelfatah, S.; Abdellatif, M.; Abdoli, A.; Abel, S.; Naumann, C.; et al., .; Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition) Autophagy 17, 1-382, (2021) DOI: 10.1080/15548627.2020.1797280

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis  updated  guidelines  for  monitoring  autophagy  in  different  organisms.  Despite  numerous  reviews, there  continues  to  be  confusion  regarding  acceptable  methods  to  evaluate  autophagy,  especially  in multicellular  eukaryotes.  Here,  we  present  a  set  of  guidelines  for  investigators  to  select  and  interpret methods  to  examine  autophagy  and  related  processes,  and  for  reviewers  to  provide  realistic  and reasonable  critiques  of  reports  that  are  focused  on  these  processes.  These  guidelines  are  not  meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being  asked  and  the  system  being  used.  Moreover,  no  individual  assay  is  perfect  for  every situation, calling  for  the  use  of  multiple  techniques  to  properly  monitor  autophagy  in  each  experimental  setting. Finally,  several  core  components  of  the  autophagy  machinery  have  been  implicated  in  distinct  auto-phagic  processes  (canonical  and  noncanonical  autophagy),  implying  that  genetic  approaches  to  block autophagy  should  rely  on  targeting  two  or  more  autophagy-related  genes  that  ideally  participate  in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation  in  the  field.
Publikation

Mercier, C.; Roux, B.; Havé, M.; Le Poder, L.; Duong, N.; David, P.; Leonhardt, N.; Blanchard, L.; Naumann, C.; Abel, S.; Cuyas, L.; Pluchon, S.; Laurent, N.; Desnos, T.; Root responses to aluminium and iron stresses require the SIZ1 SUMO ligase to modulate the STOP1 transcription factor Plant J. 108, 1507-1521, (2021) DOI: 10.1111/tpj.15525

STOP1, an Arabidopsis transcription factor favouring root growth tolerance against Al toxicity, acts in the response to iron under low Pi (-Pi). Previous studies have shown that Al and Fe regulate the stability and accumulation of STOP1 in roots, and that the STOP1 protein is sumoylated by an unknown E3 ligase. Here, using a forward genetics suppressor screen, we identified the E3 SUMO (small ubiquitin-like modifier) ligase SIZ1 as a modulator of STOP1 signalling. Mutations in SIZ1 increase the expression of ALMT1 (a direct target of STOP1) and root growth responses to Al and Fe stress in a STOP1-dependent manner. Moreover, loss-of-function mutations in SIZ1 enhance the abundance of STOP1 in the root tip. However, no sumoylated STOP1 protein was detected by western blot analysis in our sumoylation assay in E. coli, suggesting the presence of a more sophisticated mechanism. We conclude that the sumo ligase SIZ1 negatively regulates STOP1 signalling, at least in part by modulating STOP1 protein in the root tip. Our results will allow a better understanding of this signalling pathway.
Publikation

Naumann, C.; Müller, J.; Sakhonwasee, S.; Wieghaus, A.; Hause, G.; Heisters, M.; Bürstenbinder, K.; Abel, S.; The Local Phosphate Deficiency Response Activates Endoplasmic Reticulum Stress-Dependent Autophagy Plant Physiol. 179, 460-476, (2019) DOI: 10.1104/pp.18.01379

Inorganic phosphate (Pi) is often a limiting plant nutrient. In members of the Brassicaceae family, such as Arabidopsis (Arabidopsis thaliana), Pi deprivation reshapes root system architecture to favor topsoil foraging. It does so by inhibiting primary root extension and stimulating lateral root formation. Root growth inhibition from phosphate (Pi) deficiency is triggered by iron-stimulated, apoplastic reactive oxygen species generation and cell wall modifications, which impair cell-to-cell communication and meristem maintenance. These processes require LOW PHOSPHATE RESPONSE1 (LPR1), a cell wall-targeted ferroxidase, and PHOSPHATE DEFICIENCY RESPONSE2 (PDR2), the single endoplasmic reticulum (ER)-resident P5-type ATPase (AtP5A), which is thought to control LPR1 secretion or activity. Autophagy is a conserved process involving the vacuolar degradation of cellular components. While the function of autophagy is well established under nutrient starvation (C, N, or S), it remains to be explored under Pi deprivation. Because AtP5A/PDR2 likely functions in the ER stress response, we analyzed the effect of Pi limitation on autophagy. Our comparative study of mutants defective in the local Pi deficiency response, ER stress response, and autophagy demonstrated that ER stress-dependent autophagy is rapidly activated as part of the developmental root response to Pi limitation and requires the genetic PDR2-LPR1 module. We conclude that Pi-dependent activation of autophagy in the root apex is a consequence of local Pi sensing and the associated ER stress response, rather than a means for systemic recycling of the macronutrient.
Publikation

Hussain, H.; Ziegler, J.; Hause, G.; Wohlrab, J.; Neubert, R. H.; Quantitative Analysis of Free Amino Acids and Urea Derived from Isolated Corneocytes of Healthy Young, Healthy Aged, and Diseased Skin Skin Pharmacol. Physiol. 32, 94-100, (2019) DOI: 10.1159/000495992

Background/Aims: Free amino acids (FAAs) and urea, present inside the corneocytes, can be important indicators of skin condition. However, due to the lack of a standard extraction protocol for FAAs from corneocytes, conflicting research results have been reported. Therefore, the purpose of this study was (1) to standardize the extraction protocol and (2) to investigate FAA profiles in healthy young and healthy old volunteers, as well as in psoriasis and atopic dermatitis patients. Methods: Skin samples were collected from four groups (healthy young, healthy old, and psoriasis and atopic dermatitis patients) with 5 volunteers per group. Corneocytes were isolated and examined microscopically. FAAs and urea were extracted from the isolated corneocytes, and their amounts were quantified using LC-ESI/MS/MS (after derivatization with Fmoc-Cl) and colorimetric methods, respectively. Results: The micrographs of the corneocytes showed no morphological features attributable to age or disease conditions. The highest and lowest concentrations of total FAAs and urea were observed in the healthy old group and the healthy young group, respectively. Unlike the other FAAs and urea, citrulline was found at a higher level in the healthy young group than in the disease groups. Conclusion: This study suggests that the levels of FAAs and urea in the skin are affected by age and skin conditions (healthy/diseased). However, further studies are needed to show the effects of different skin conditions on the levels of FAAs and urea.
Publikation

Bürstenbinder, K.; Möller, B.; Plötner, R.; Stamm, G.; Hause, G.; Mitra, D.; Abel, S.; The IQD Family of Calmodulin-Binding Proteins Links Calcium Signaling to Microtubules, Membrane Subdomains, and the Nucleus Plant Physiol. 173, 1692-1708, (2017) DOI: 10.1104/pp.16.01743

Calcium (Ca2+) signaling and dynamic reorganization of the cytoskeleton are essential processes for the coordination and control of plant cell shape and cell growth. Calmodulin (CaM) and closely related calmodulin-like (CML) polypeptides are principal sensors of Ca2+ signals. CaM/CMLs decode and relay information encrypted by the second messenger via differential interactions with a wide spectrum of targets to modulate their diverse biochemical activities. The plant-specific IQ67 DOMAIN (IQD) family emerged as possibly the largest class of CaM-interacting proteins with undefined molecular functions and biological roles. Here, we show that the 33 members of the IQD family in Arabidopsis (Arabidopsis thaliana) differentially localize, using green fluorescent protein (GFP)-tagged proteins, to multiple and distinct subcellular sites, including microtubule (MT) arrays, plasma membrane subdomains, and nuclear compartments. Intriguingly, the various IQD-specific localization patterns coincide with the subcellular patterns of IQD-dependent recruitment of CaM, suggesting that the diverse IQD members sequester Ca2+-CaM signaling modules to specific subcellular sites for precise regulation of Ca2+-dependent processes. Because MT localization is a hallmark of most IQD family members, we quantitatively analyzed GFP-labeled MT arrays in Nicotiana benthamiana cells transiently expressing GFP-IQD fusions and observed IQD-specific MT patterns, which point to a role of IQDs in MT organization and dynamics. Indeed, stable overexpression of select IQD proteins in Arabidopsis altered cellular MT orientation, cell shape, and organ morphology. Because IQDs share biochemical properties with scaffold proteins, we propose that IQD families provide an assortment of platform proteins for integrating CaM-dependent Ca2+ signaling at multiple cellular sites to regulate cell function, shape, and growth.
Publikation

Otto, M.; Naumann, C.; Brandt, W.; Wasternack, C.; Hause, B.; Activity Regulation by Heteromerization of Arabidopsis Allene Oxide Cyclase Family Members Plants 5, 3, (2016) DOI: 10.3390/plants5010003

Jasmonates (JAs) are lipid-derived signals in plant stress responses and development. A crucial step in JA biosynthesis is catalyzed by allene oxide cyclase (AOC). Four genes encoding functional AOCs (AOC1, AOC2, AOC3 and AOC4) have been characterized for Arabidopsis thaliana in terms of organ- and tissue-specific expression, mutant phenotypes, promoter activities and initial in vivo protein interaction studies suggesting functional redundancy and diversification, including first hints at enzyme activity control by protein-protein interaction. Here, these analyses were extended by detailed analysis of recombinant proteins produced in Escherichia coli. Treatment of purified AOC2 with SDS at different temperatures, chemical cross-linking experiments and protein structure analysis by molecular modelling approaches were performed. Several salt bridges between monomers and a hydrophobic core within the AOC2 trimer were identified and functionally proven by site-directed mutagenesis. The data obtained showed that AOC2 acts as a trimer. Finally, AOC activity was determined in heteromers formed by pairwise combinations of the four AOC isoforms. The highest activities were found for heteromers containing AOC4 + AOC1 and AOC4 + AOC2, respectively. All data are in line with an enzyme activity control of all four AOCs by heteromerization, thereby supporting a putative fine-tuning in JA formation by various regulatory principles.
Publikation

Müller, J.; Toev, T.; Heisters, M.; Teller, J.; Moore, K.; Hause, G.; Dinesh, D.; Bürstenbinder, K.; Abel, S.; Iron-Dependent Callose Deposition Adjusts Root Meristem Maintenance to Phosphate Availability Dev. Cell 33, 216-230, (2015) DOI: 10.1016/j.devcel.2015.02.007

Plant root development is informed by numerous edaphic cues. Phosphate (Pi) availability impacts the root system architecture by adjusting meristem activity. However, the sensory mechanisms monitoring external Pi status are elusive. Two functionally interacting Arabidopsis genes, LPR1 (ferroxidase) and PDR2 (P5-type ATPase), are key players in root Pi sensing, which is modified by iron (Fe) availability. We show that the LPR1-PDR2 module facilitates, upon Pi limitation, cell-specific apoplastic Fe and callose deposition in the meristem and elongation zone of primary roots. Expression of cell-wall-targeted LPR1 determines the sites of Fe accumulation as well as callose production, which interferes with symplastic communication in the stem cell niche, as demonstrated by impaired SHORT-ROOT movement. Antagonistic interactions of Pi and Fe availability control primary root growth via meristem-specific callose formation, likely triggered by LPR1-dependent redox signaling. Our results link callose-regulated cell-to-cell signaling in root meristems to the perception of an abiotic cue.
  • Die Leibniz-Gemeinschaft
  • Digitalisierung in der Landwirtschaft
  • Martin-Luther Universität Halle
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