Anton Schäffner and his colleagues are keen on revealing molecular mechanisms how plants develop and interact with their environment. His interests focus on (i) the role aquaporins in the plasma membrane of plants, which he and his student Werner Kammerloher discovered in 1994, in plant water relation and plant development and (ii) on signaling and control of plant defense against pathogens, a theme that was initiated by Veronica von Saint Paul in our laboratory in 2011.
Anton Schäffner studied chemistry to be prepared for an in-depth understanding of molecular processes. This general wish was coupled with the vision of understanding plants as the fundamental and beautiful basis for our life. Therefore, he embarked the at that time emerging field of plant molecular biology during his postdoctorate with Jen Sheen at the Massachusetts General Hospital, Harvard University, Boston, MA, USA from 1988 -1990. Back in Germany, he established an independent research group from 1990 – 1997 at the Ludwig-Maximilians-Universtität München (LMU). In 1996, he achieved his habilitations and, since then, is a member of the Faculty of Chemistry and Pharmacy at the LMU München. In 1997, he established a research group “Molecular Plant Physiology” at the Helmholtz Zentrum München. The model plant Arabidopsis thaliana is our main experimental system.
Since spring 2023, Anton Schäffner also supports the Strategy, Programs, and Resources Unit Project Funding, which assists third-party funding applications by scientists at the center.
BiochemistryPlant genetics AquaporinsPlant defense signalingGlycosyltransferases Plant microtubules Support of third-party project funding
Research Group Leader at Helmholtz Center Munich
Lecturer (Biochemistry) at LMU München, Faculty of Chemistry and Biochemistry
Highlight PublicationsSee all
2023 EMBO Reports e56754
The use of beneficial microbes to mitigate drought stress tolerance of plants is of great potential albeit little understood. We show here that a root endophytic desert bacterium, Pseudomonas argentinensis strain SA190, enhances drought stress tolerance in Arabidopsis. Transcriptome and genetic analysis demonstrate that SA190-induced root morphogenesis and gene expression is mediated via the plant abscisic acid (ABA) pathway. Moreover, we demonstrate that SA190 primes the promoters of target genes in an epigenetic ABA-dependent manner. Application of SA190 priming on crops is demonstrated for alfalfa, showing enhanced performance under drought conditions. In summary, a single beneficial root bacterial strain can help plants to resist drought conditions.
Defense responses in plants are based on complex biochemical processes. Systemic acquired resistance (SAR) helps to fight infections by (hemi-)biotrophic pathogens. One important signaling molecule in SAR is pipecolic acid (Pip), accumulation of which is dependent on the aminotransferase ALD1 in Arabidopsis. While exogenous Pip primes defense responses in the monocotyledonous cereal crop barley (Hordeum vulgare), it is currently unclear if endogenous Pip plays a role in disease resistance in monocots. Here, we generated barley ald1 mutants using CRISPR/Cas9, and assessed their capacity to mount SAR. Endogenous Pip levels were reduced after infection of the ald1 mutant, and this altered systemic defense against the fungus Blumeria graminis f. sp. hordei. Furthermore, Hvald1 plants did not emit nonanal, one of the key volatile compounds that are normally emitted by barley plants after the activation of SAR. This resulted in the inability of neighboring plants to perceive and/or respond to airborne cues and prepare for an upcoming infection, although HvALD1 was not required in the receiver plants to mediate the response. Our results highlight the crucial role of endogenous HvALD1 and Pip for SAR, and associate Pip, in particular together with nonanal, with plant-to-plant defense propagation in the monocot crop barley.
Glucosylation modulates the biological activity of small molecules and frequently leads to their inactivation. The Arabidopsis thaliana glucosyltransferase UGT76B1 is involved in conjugating the stress hormone salicylic acid (SA) as well as isoleucic acid (ILA). Here, we show that UGT76B1 also glucosylates N-hydroxypipecolic acid (NHP), which is synthesized by FLAVIN-DEPENDENT MONOOXYGENASE 1 (FMO1) and activates systemic acquired resistance (SAR). Upon pathogen attack, Arabidopsis leaves generate two distinct NHP hexose conjugates, NHP-O-b-glucoside and NHP glucose ester, whereupon only NHP-O-b-glucoside formation requires a functional SA pathway. The ugt76b1 mutants speciﬁcally fail to generate the NHP-O-b-glucoside, and recombinant UGT76B1 synthesizes NHP-O-b-glucoside in vitro in competition with SA and ILA. The loss of UGT76B1 elevates the endogenous levels of NHP, SA, and ILA and establishes a constitutive SAR-like immune status. Introgression of the fmo1 mutant lacking NHP biosynthesis into the ugt76b1 background abolishes this SAR-like resistance. Moreover, overexpression of UGT76B1 in Arabidopsis shifts the NHP and SA pools toward O-b-gluco- side formation and abrogates pathogen-induced SAR. Our results further indicate that NHP-triggered immunity is SA- dependent and relies on UGT76B1 as a common metabolic hub. Thereby, UGT76B1-mediated glucosylation controls the levels of active NHP, SA, and ILA in concert to balance the plant immune status.
2021 Phytochemistry 186, 112738
Isoleucic acid (ILA), a branched-chain amino acid-related 2-hydroxycarboxylic acid, occurs ubiquitously in plants. It enhances pathogen resistance and inhibits root growth of Arabidopsis. The salicylic acid (SA) glucosyltransferase UGT76B1 is able to conjugate ILA. Here, we investigate the role of ILA in planta in Arabidopsis and reveal a triad of distinct responses to this small molecule. ILA synergistically co-operates with SA to activate SA-responsive gene expression and resistance in a UGT76B1-dependent manner in agreement with the observed competitive ILA-dependent repression of SA glucosylation by UGT76B1. However, ILA also shows an SA-independent stress response. Nitroblue tetrazolium staining and pharmacological experiments indicate that ILA induces superoxide formation of the wild type and of an SA-deficient (NahG sid2) line. In contrast, the inhibitory effect of ILA on root growth is independent of both SA and superoxide induction. These effects of ILA are specific and distinct from its isomeric compound leucic acid and from the amino acid isoleucine. Leucic acid and isoleucine do not induce expression of defense marker genes or superoxide production, whereas both compounds inhibit root growth. All three responses to ILA are also observed in Brassica napus.
Throughout the temperate zones, plants face combined drought and heat spells in increasing frequency and intensity. Here, we compared periodic (intermittent, i.e., high-frequency) versus chronic (continuous, i.e., high-intensity) drought-heat stress scenarios in gray poplar (Populus3 canescens) plants for phenotypic and transcriptomic effects during stress and after recovery. Photosynthetic productivity after stress recovery exceeded the performance of poplar trees without stress experience. We analyzed the molecular basis of this stress-related memory phenotype and investigated gene expression responses across ﬁve major tree compartments including organs and wood tissues. For each of these tissue samples, transcriptomic changes induced by the two stress scenarios were highly similar during the stress phase but strikingly divergent after recovery. Characteristic molecular response patterns were found across tissues but involved different genes in each tissue. Only a small fraction of genes showed similar stress and recovery expression proﬁles across all tissues, including type 2C protein phosphatases, the LATE EMBRYOGENESIS ABUNDANT PROTEIN4-5 genes, and homologs of the Arabidopsis (Arabidopsis thaliana) transcription factor HOMEOBOX7. Analysis of the predicted transcription factor regulatory networks for these genes suggested that a complex interplay of common and tissue-speciﬁc components contributes to the coordination of post-recovery responses to stress in woody plants.
Background: Elevated temperature and reduced water availability are frequently linked abiotic stresses that may provoke distinct as well as interacting molecular responses. Based on non-targeted metabolomic and transcriptomic measurements from Arabidopsis rosettes, this study aims at a systematic elucidation of relevant components in different drought and heat scenarios as well as relationships between molecular players of stress response. Results: In combined drought-heat stress, the majority of single stress responses are maintained. However, interaction effects between drought and heat can be discovered as well; these relate to protein folding, flavonoid biosynthesis and growth inhibition, which are enhanced, reduced or specifically induced in combined stress, respectively. Heat stress experiments with and without supplementation of air humidity for maintenance of vapor pressure deficit suggest that decreased relative air humidity due to elevated temperature is an important component of heat stress, specifically being responsible for hormone-related responses to water deprivation. Remarkably, this “dry air effect” is the primary trigger of the metabolomic response to heat. In contrast, the transcriptomic response has a substantial temperature component exceeding the dry air component and including up-regulation of many transcription factors and protein folding-related genes. Data level integration independent of prior knowledge on pathways and condition labels reveals shared drought and heat responses between transcriptome and metabolome, biomarker candidates and co-regulation between genes and metabolic compounds, suggesting novel players in abiotic stress response pathways. Conclusions: Drought and heat stress interact both at transcript and at metabolite response level. A comprehensive, non-targeted view of this interaction as well as non-interacting processes is important to be taken into account when improving tolerance to abiotic stresses in breeding programs. Transcriptome and metabolome may respond with different extent to individual stress components. Their contrasting behavior in response to temperature stress highlights that the protein folding machinery effectively shields the metabolism from stress. Disentangling the complex relationships between transcriptome and metabolome in response to stress is an enormous challenge. As demonstrated by case studies with supporting evidence from additional data, the large dataset provided in this study may assist in determining linked genetic and metabolic features as candidates for future mechanistic analyses.
The non-essential cation caesium (Cs+) is assimilated by all organisms. Thus, anthropogenically released radiocaesium is of concern to agriculture. Cs+ accumulates owing to its chemical similarity to the potassium ion (K+). The apparent lack of a Cs+ -speciﬁc uptake mechanism has obstructed attempts to manipulate Cs+ accumulation without causing pleiotropic effects. Here we show that the SNARE protein Sec22p/SEC22 speciﬁcally impacts Cs+ accumulation in yeast and in plants. Loss of Saccharomyces cerevisiae Sec22p does not affect K þ homeostasis, yet halves Cs+ concentration compared with the wild type. Mathematical modelling of the uptake time course predicts a compromised vacuolar Cs+ deposition in sec22D. Biochemical fractionation conﬁrms this and indicates a new feature of Sec22p in enhancing non-selective cation deposition. A developmentally controlled loss-of-function mutant of the orthologous Arabidopsis thaliana SEC22 phenocopies the reduced Cs+ uptake without affecting plant growth. This ﬁnding provides a new strategy to reduce radiocaesium entry into the food chain.
Aquaporins are membrane channels that facilitate water movement across cell membranes. In plants, aquaporins contribute to water relations. Here, we establish a new link between aquaporin-dependent tissue hydraulics and auxin-regulated root development in Arabidopsis thaliana. We report that most aquaporin genes are repressed during lateral root formation and by exogenous auxin treatment. Auxin reduces root hydraulic conductivity both at the cell and whole-organ levels. The highly expressed aquaporin PIP2;1 is progressively excluded from the site of the auxin response maximum in lateral root primordia (LRP) whilst being maintained at their base and underlying vascular tissues. Modelling predicts that the positive and negative perturbations of PIP2;1 expression alter water ﬂow into LRP, thereby slowing lateral root emergence (LRE). Consistent with this mechanism, pip2;1 mutants and PIP2;1-overexpressing lines exhibit delayed LRE. We conclude that auxin promotes LRE by regulating the spatial and temporal distribution of aquaporin-dependent root tissue water transport.
Plants coordinate and tightly regulate pathogen defense by the mostly antagonistic salicylate (SA)- and jasmonate (JA)-mediated signaling pathways. Here, we show that the previously uncharacterized glucosyltransferase UGT76B1 is a novel player in this SA-JA signaling crosstalk. UGT76B1 was selected as the top stress-induced isoform among all 122 members of the Arabidopsis thaliana UGT family. Loss of UGT76B1 function leads to enhanced resistance to the biotrophic pathogen Pseudomonas syringae and accelerated senescence but increased susceptibility toward necrotrophic Alternaria brassicicola. This is accompanied by constitutively elevated SA levels and SA-related marker gene expression, whereas JA-dependent markers are repressed. Conversely, UGT76B1 overexpression has the opposite effect. Thus, UGT76B1 attenuates SA-dependent plant defense in the absence of infection, promotes the JA response, and delays senescence. The ugt76b1 phenotypes were SA dependent, whereas UGT76B1 overexpression indicated that this gene possibly also has a direct effect on the JA pathway. Nontargeted metabolomic analysis of UGT76B1 knockout and overexpression lines using ultra-high-resolution mass spectrometry and activity assays with the recombinant enzyme led to the ab initio identiﬁcation of isoleucic acid (2-hydroxy-3-methyl-pentanoic acid) as a substrate of UGT76B1. Exogenously applied isoleucic acid increased resistance against P. syringae infection. These ﬁndings indicate a novel link between amino acid–related molecules and plant defense that is mediated by small-molecule glucosylation.
Several factors regulate plant organ growth polarity. tortifolia2 (tor2), a right-handed helical growth mutant, has a conservative replacement of Arg-2 with Lys in the a-tubulin 4 protein. Based on a published high-resolution (2.89 A˚) tubulin structure, we predict that Arg-2 of a-tubulin forms hydrogen bonds with the GTPase domain of b-tubulin, and structural modeling suggests that these contacts are interrupted in tor2. Consistent with this, we found that microtubule dynamicity is reduced in the tor2 background. We investigated the developmental origin of the helical growth phenotype using tor2. One hypothesis predicts that cell division patterns cause helical organ growth in Arabidopsis thaliana mutants. However, cell division patterns of tor2 root tips appear normal. Experimental uncoupling of cell division and expansion suggests that helical organ growth is based on cell elongation defects only. Another hypothesis is that twisting is due to inequalities in expansion of epidermal and cortical tissues. However, freely growing leaf trichomes of tor2 mutants show right-handed twisting and cortical microtubules form left-handed helices as early as the unbranched stage of trichome development. Trichome twisting is inverted in double mutants with tor3, a left-handed mutant. Single tor2 suspension cells also exhibit handed twisting. Thus, twisting of tor2 mutant organs appears to be a higher-order expression of the helical expansion of individual cells.
Plants can grow straight or in the twisted fashion exhibited by the helical growth of some climbing plants. Analysis of helical-growth mutants from Arabidopsis has indicated that microtubules are involved in the expression of the helical phenotype. Arabidopsis mutants growing with a right-handed twist have been reported to have cortical microtubules that wind around the cell in left-handed helices and vice versa. Microtubular involvement is further suspected from the finding that some helical mutants are caused by single amino acid substitutions in α-tubulin and because of the sensitivity of the growth pattern to anti-microtubule drugs. Insight into the roles of microtubules in organ elongation is anticipated from analyses of genes defined by helical mutations. We investigated the helical growth of the Arabidopsis mutant tortifolia1/spiral2 (tor1/spr2), which twists in a right-handed manner, and found that this correlates with a complex reorientation of cortical microtubules. TOR1 was identified by a map-based approach; analysis of the TOR1 protein showed that it is a member of a novel family of plant-specific proteins containing N-terminal HEAT repeats. Recombinant TOR1 colocalizes with cortical microtubules in planta and binds directly to microtubules in vitro. This shows that TOR1 is a novel, plant-specific microtubule-associated protein (MAP) that regulates the orientation of cortical microtubules and the direction of organ growth.
Aquaporins are ubiquitous channel proteins that facilitate the transport of water across cell membranes. Aquaporins show a typically high isoform multiplicity in plants, with 35 homologs in Arabidopsis. The integrated function of plant aquaporins and the function of each individual isoform remain poorly understood. Matrix-assisted laser desorption/ ionization time-of-flight analyses suggested that Plasma Membrane Intrinsic Protein2;2 (PIP2;2) is one of the abun- dantly expressed aquaporin isoforms in Arabidopsis root plasma membranes. Two independent Arabidopsis knockout mutants of PIP2;2 were isolated using a PCR-based strategy from a library of plant lines mutagenized by the insertion of Agrobacterium tumefaciens T-DNA. Expression in transgenic Arabidopsis of a PIP2;2 promoter–beta-glucuronidase gene fusion indicated that PIP2;2 is expressed predominantly in roots, with a strong expression in the cortex, endodermis, and stele. The hydraulic conductivity of root cortex cells, as measured with a cell pressure probe, was reduced by 25 to 30% in the two allelic PIP2;2 mutants compared with the wild type. In addition, free exudation measurements revealed a 14% decrease, with respect to wild-type values, in the osmotic hydraulic conductivity of roots excised from the two PIP2;2 mutants. Together, our data provide evidence for the contribution of a single aquaporin gene to root water uptake and identify PIP2;2 as an aquaporin specialized in osmotic fluid transport. PIP2;2 has a close homolog, PIP2;3, showing 96.8% amino acid identity. The phenotype of PIP2;2 mutants demonstrates that, despite their high homology and isoform multiplicity, plant aquaporins have evolved with nonredundant functions.
Expression in mammalian COS cells and an efficient microtiter-based strategy for immunoselectlon was used in a novel approach to identify genes encoding plant membrane proteins. COS cells were transfected with an Arabidopsis thaliana root cDNA library constructed in a bacterial mammalian shuffle vector and screened with an antiserum raised against purified deglycosylated integral plasma membrane proteins from A. thallana roots. Antibodies directed against a prominent 27 kDa antigen led to the identification of five different genes. They comprised two subfamilies related to the major intrinsic protein (MIP) superfamily and were named plasma membrane intrinsic proteins, PIP1 and PIP2, since the cellular localization of PIP1 and most probably PIP2 proteins in the plasma membrane was independently confirmed by their co- segregation with marker enzymes during aequeous two-phase partitioning. Surprisingly, expression in Xenopus laevis oocytes revealed that all five PIP mRNAs coded for Hg2+-sensitive water transport facilitating activities. There had been no previous evidence of the existence of water channels in the plasma membrane of plant cells and the high diffusional water permeability of the lipid bilayer was considered to be sufficient for water exchange. Neverthelese, Northern and Western analyses showed that the PIP genes are constitutively and possibly even redundantly expressed from the small A. thaliana genome.