Synthesis and hydrolysis of auxins and their conjugates with different side-chain lengths: are all products active auxins?

Plants need hormone substances to regulate a plethora of responses during their life cycle. One major hormone class is called auxin, which is involved in many developmental processes. Besides the major auxin indole-3-acetic acid, there are other auxin-like molecules present in some, but not in all plants, an example would be chlorinated IAA in legumes. Among these are also the auxins with longer chains, indole-3-propionic acid and indole-3-butyric acid. The auxin-dependent growth response is dependent on the concentration of the compound. While lower concentrations are mainly growth promoting, high concentrations are actually inhibiting some developmental processes. Therefore, tight control of the auxin concentration is essential for proper growth and development. This can be achieved by altering the amount of active auxin via transport, biosynthesis, degradation or reversible conjugation to small molecules. In addition, plants use auxin during their interaction with the environment, for example during abiotic stresses such as salt, temperature or water stress to adapt the growth responses specifically. Furthermore, auxin is involved in the development of plant disease symptoms, such as tumor growth or aberrant tissue formation. However, together with other plant hormones such as salicylic acid auxin can also modulate disease progression or resistance in different plant – microbe combinations. </p

Auxin Amidohydrolases – From Structure to Function: Revisited

The control of plant growth and development is a well-coordinated process between exogenous and endogenous signals. Auxins are plant hormones belonging to the endogenous signals, which control a vast array of different processes. While auxins are growth promoting at low concentrations, higher levels are often inhibitory. Therefore, the tight control of auxin concentrations in a given plant tissue is essential. Among several processes that participate in auxin homeostasis, we focused herein on the process of reversible auxin conjugation that considers the synthesis of inactive auxin conjugates, which can be hydrolyzed back to the active form by so called auxin conjugate hydrolases. Although these proteins have been known for quite some time, their role in plants is still not clear, especially since novel hydrolases with different substrate specificities have been isolated. Thus, we have revisited the knowledge about auxin hydrolases, from their structure and biochemistry to the role in plant development and in dealing with unfavorable climate conditions. This work is licensed under a Creative Commons Attribution 4.0 International License

A Novel Target (Oxidation Resistant 2) in Arabidopsis thaliana to Reduce Clubroot Disease Symptoms via the Salicylic Acid Pathway without Growth Penalties

The clubroot disease (Plasmodiophora brassicae) is one of the most damaging diseases worldwide among brassica crops. Its control often relies on resistant cultivars, since the manipulation of the disease hormones, such as salicylic acid (SA) alters plant growth negatively. Alternatively, the SA pathway can be increased by the addition of beneficial microorganisms for biocontrol. However, this potential has not been exhaustively used. In this study, a recently characterized protein Oxidation Resistant 2 (OXR2) from Arabidopsis thaliana is shown to increase the constitutive pathway of SA defense without decreasing plant growth. Plants overexpressing AtOXR2 (OXR2-OE) show strongly reduced clubroot symptoms with improved plant growth performance, in comparison to wild type plants during the course of infection. Consequently, oxr2 mutants are more susceptible to clubroot disease. P. brassicae itself was reduced in these galls as determined by quantitative real-time PCR. Furthermore, we provide evidence for the transcriptional downregulation of the gene encoding a SA-methyltransferase from the pathogen in OXR2-OE plants that could contribute to the phenotype.Fil: Mencia, Regina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Welchen, Elina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Agrobiotecnología del Litoral. Universidad Nacional del Litoral. Instituto de Agrobiotecnología del Litoral; ArgentinaFil: Auer, Susann. Technische Universität Dresden; AlemaniaFil: Ludwig Müller, Jutta. Technische Universität Dresden; Alemani

Genetically transformed roots: From plant disease to biotechnological resource

Hairy root syndrome is a disease that is induced by Agrobacterium rhizogenes infection and characterized by a proliferation of excessively branching roots. However, in the past 30 years A. rhizogenes-mediated transformation has also provided a valuable platform for studying biosynthesis pathways in plants. Furthermore, the genetically transformed root cultures are becoming increasingly attractive, cost-effective options for mass-producing desired plant metabolites and expressing foreign proteins. Numerous proof-of-concept studies have demonstrated the feasibility of scaling up hairy-root-based processes while maintaining their biosynthetic potential. Recently, hairy roots have also shown immense potential for applications in phytoremediation, that is, plant-based decontamination of polluted environments. This review highlights recent progress and limitations in the field, and outlines future perspectives for the industrial exploitation of hairy roots.Fil: Georgiev, Milen I.. Bulgarian Academy of Sciences; Bulgaria. Leiden University; Países BajosFil: Agostini, Elizabeth. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Ludwig Müller, Jutta. Technische Universitat Dresden; AlemaniaFil: Xu, Jianfeng. University of Arkansas for Medical Sciences; Estados Unido

Improvement of root architecture under abiotic stress through control of auxin homeostasis in Arabidopsis and Brassica crops

Auxin plays an important role in many aspects of plant development including stress responses. Here we briefly summarize how auxin is involved in salt stress, drought (i.e. mostly osmotic stress), waterlogging and nutrient deficiency in Brassica plants. In addition, some mechanisms to control auxin levels and signaling in relation to root formation (under stress) will be reviewed. Molecular studies are mainly described for the model plant Arabidopsis thaliana, but we also like to demonstrate how this knowledge can be transferred to agriculturally important Brassica species, such as Brassica rapa, Brassica napus and Brassica campestris. Moreover, beneficial fungi could play a role in the adaptation response of Brassica roots to abiotic stresses. Therefore, the possible influence of Piriformospora indica will also be covered since the growth promoting response of plants colonized by P. indica is also linked to plant hormones, among them auxin

The paramutated SULFUREA locus of tomato is involved in auxin biosynthesis

The tomato (Solanum lycopersicum) sulfurea mutation displays trans-inactivation of wild-type alleles in heterozygous plants, a phenomenon referred to as paramutation. Homozygous mutant plants and paramutated leaf tissue of heterozygous plants show a pigment-deficient phenotype. The molecular basis of this phenotype and the function of the SULFUREA gene (SULF) are unknown. Here, a comprehensive physiological analysis of the sulfurea mutant is reported which suggests a molecular function for the SULFUREA locus. It is found that the sulf mutant is auxin-deficient and that the pigment-deficient phenotype is likely to represent only a secondary consequence of the auxin deficiency. This is most strongly supported by the isolation of a suppressor mutant which shows an auxin overaccumulation phenotype and contains elevated levels of indole-3-acetic acid (IAA). Several lines of evidence point to a role of the SULF gene in tryptophan-independent auxin biosynthesis, a pathway whose biochemistry and enzymology is still completely unknown. Thus, the sulfurea mutant may provide a promising entry point into elucidating the tryptophan-independent pathway of IAA synthesis

Evidence for the Early Evolutionary Loss of the M20D Auxin Amidohydrolase Family from Mosses and Horizontal Gene Transfer from Soil Bacteria of Cryptic Hydrolase Orthologues to Physcomitrella patens

Inactive auxin conjugates are accumulated in plants and hydrolyzed to recover phytohormone action. A family of metallopeptidase orthologues has been conserved in Plantae to help regulate auxin homeostatic levels during growth and development. This hydrolase family was recently traced back to liverwort, the most ancient extant land plant lineage. Liverwort’s auxin hydrolase has little activity against auxin conjugate substrates and does not appear to actively regulate auxin. This finding, along with data that shows moss can synthesize auxin conjugates, led to examining another bryophyte lineage, Physcomitrella patens. We have identified and isolated three M20D hydrolase paralogues from moss. The isolated enzymes strongly recognize and cleave a variety of auxin conjugates, including those of indole butyric and indole propionic acids. These P. patens hydrolases not only appear to be “cryptic”, but they are likely to have derived from soil bacteria through Horizontal Gene Transfer. Additionally, support is presented that the plant-type M20D peptidase family may have been universally lost from mosses after divergence from the common ancestor with liverwort

Praćenje metabolizma flavonoida u humanim stanicama na temelju fluorescencije izazvane interakcijom kvercetina s proteinima

Despite the wealth of information concerning biological effects of flavonoids, a systematic approach to analyzing the molecular targets is still lacking and, for this reason, a rational evaluation of the risks or benefits of flavonoid-containing foods or of possible pharmaceutical applications is difficult. We have exploited the property of quercetin to elicit fluorescence when bound to specific target proteins and assayed several flavonoids with different modifications (methylation, hydroxylation, glycosylation). Quercetin target proteins can be visualized in living cells, but in vital human leukaemia cells (HL-60) the fluorescence decreases rapidly after labelling, while metabolically inactive apoptotic cells retain the fluorescence. These cytological differences were apparent under the fluorescent microscope and were quantified using flow cytometry. Metabolic conversion of quercetin in vital cells was confirmed and quantified by HPLC analysis. While apoptotic cells still contained considerable amounts of quercetin, vital cells rapidly metabolized the flavonoid (e.g., by methylation or glycosylation). Biochemical results are consistent with the cytological observations and support the conclusion that quercetin becomes rapidly converted to non-fluorogenic metabolites in vital cells. Loss of fluorescence in vital cells allows convenient monitoring and quantifying of the dynamics of quercetin metabolism in human cells.Unatoč mnoštvu informacija koje se odnose na biološke učinke flavonoida, sustavni pristup analizi njihovih ciljnih molekula još uvijek nedostaje. Iz toga razloga vrlo je teško racionalno vrednovati opasnosti ili koristi koje donosi hrana koja sadrži flavonoide kao i njihovu moguću farmakološku primjenu. Iskoristili smo svojstvo kvercetina da izazove fluorescenciju kada se veže za specifične ciljne proteine i analizirali nekoliko različito modificiranih flavonoida (metilacija, hidroksilacija, glikozilacija). Ciljni proteini za koje se kvercetin veže u živim stanicama mogu se vizualizirati na temelju fluorescencije. U živim stanicama humane leukemije (HL-60) fluorescencija naglo pada nakon označavanja flavonoidima, dok metabolički inaktivne apoptotične stanice zadržavaju fluorescenciju. Te su citološke razlike jasno zapažene pod fluorescencijskim mikroskopom, a kvantificirane su pomoću protočne citometrije. Metabolička pretvorba kvercetina u živim stanicama potvr|ena je i kvantificirana pomoću HPLC analiza. Dok apoptotične stanice zadržavaju značajnu količinu kvercetina, žive ga stanice brzo metaboliziraju (npr. metilacijom ili glikozilacijom). Ti su biokemijski rezultati u skladu s citološkim promatranjima i podupiru zaključak da se kvercetin u živim stanicama brzo pretvara u nefluorogene metabolite. Gubitak fluorescencije u živim stanicama omogućava praćenje i kvantifikaciju dinamike metabolizma kvercetina u humanim stanicama

The Clubroot Pathogen (\u3ci\u3ePlasmodiophora brassicae\u3c/i\u3e) Influences Auxin Signaling to Regulate Auxin Homeostasis in Arabidopsis

The clubroot disease, caused by the obligate biotrophic protist Plasmodiophora brassicae, affects cruciferous crops worldwide. It is characterized by root swellings as symptoms, which are dependent on the alteration of auxin and cytokinin metabolism. Here, we describe that two different classes of auxin receptors, the TIR family and the auxin binding protein 1 (ABP1) in Arabidopsis thaliana are transcriptionally upregulated upon gall formation. Mutations in the TIR family resulted in more susceptible reactions to the root pathogen. As target genes for the different pathways we have investigated the transcriptional regulation of selected transcriptional repressors (Aux/IAA) and transcription factors (ARF). As the TIR pathway controls auxin homeostasis via the upregulation of some auxin conjugate synthetases (GH3), the expression of selected GH3 genes was also investigated, showing in most cases upregulation. A double gh3 mutant showed also slightly higher susceptibility to P. brassicae infection, while all tested single mutants did not show any alteration in the clubroot phenotype. As targets for the ABP1-induced cell elongation the effect of potassium channel blockers on clubroot formation was investigated. Treatment with tetraethylammonium (TEA) resulted in less severe clubroot symptoms. This research provides evidence for the involvement of two auxin signaling pathways in Arabidopsis needed for the establishment of the root galls by P. brassicae