7-rhamnosylated flavonols modulate homeostasis of the plant hormone auxin and affect plant development

Flavonols are a group of secondary metabolites that affect diverse cellular processes. They are considered putative negative regulators of the transport of the phytohormone auxin, by which they influence auxin distribution and concomitantly take part in the control of plant organ development. Flavonols are accumulating in a large number of glycosidic forms. Whether these have distinct functions and diverse cellular targets is not well understood. The rol1-2 mutant of Arabidopsis thaliana is characterized by a modified flavonol glycosylation profile that is inducing changes in auxin transport and growth defects in shoot tissues. To determine whether specific flavonol glycosides are responsible for these phenotypes, a suppressor screen was performed on the rol1-2 mutant, resulting in the identification of an allelic series of UGT89C1, a gene encoding a flavonol 7-O-rhamnosyltransferase. A detailed analysis revealed that interfering with flavonol rhamnosylation increases the concentration of auxin precursors and auxin metabolites, whereas auxin transport is not affected. This finding provides an additional level of complexity to the possible ways by which flavonols influence auxin distribution and suggests that flavonol glycosides play an important role in regulating plant development

New insights into auxin metabolism in Bradyrhizobium japonicum

Bacterial metabolism of phytohormones includes several processes such as biosynthesis, catabolism, conjugation, hydrolysis and homeostatic regulation. However, only biosynthesis and occasionally catabolism are studied in depth in microorganisms. In this work, we evaluated and reconsidered IAA metabolism in Bradyrhizobium japonicum E109, one of the most widely used strains for soybean inoculation around the world. The genomic analysis of the strain showed the presence of several genes responsible for IAA biosynthesis, mainly via indole-3-acetonitrile (IAN), indole-3-acetamide (IAM) and tryptamine (TAM) pathways. However; in vitro experiments showed that IAA is not accumulated in the culture medium in significant amounts. On the contrary, a strong degradation activity was observed after exogenous addition of 0.1 mM of IAA, IBA or NAA to the medium. B. japonicum E109 was not able to grow in culture medium containing IAA as a sole carbon source. In YEM medium, the bacteria degraded IAA and hydrolyzed amino acid auxin conjugates with alanine (IAAla), phenylalanine (IAPhe), and leucine (IAPhe), releasing IAA which was quickly degraded. Finally, the presence of exogenous IAA induced physiological changes in the bacteria such as increased biomass and exopolysaccharide production, as well as infection effectiveness and symbiotic behavior in soybean plants.Fil: Torres, Daniela Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-microorganismo; ArgentinaFil: Benavidez, Iliana. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-microorganismo; ArgentinaFil: Donadío, Evelyn Florencia. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-microorganismo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Mongiardini, Elias Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Biotecnología y Biología Molecular. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Biotecnología y Biología Molecular; ArgentinaFil: Rosas, Susana Beatriz. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-microorganismo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Spaepen, Stijn. Max Planck Institute for Plant Breeding Research; Alemania. Katholikie Universiteit Leuven; BélgicaFil: Vanderleyden, Jozef. Katholikie Universiteit Leuven; BélgicaFil: Pencík, Ales. Palacký University; República ChecaFil: Novák, Ondrej. Palacký University; República ChecaFil: Strnad, Miroslav. Palacký University; República ChecaFil: Frébortová, Jitka. Palacký University; República ChecaFil: Cassan, Fabricio Dario. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Departamento de Ciencias Naturales. Laboratorio de Fisiología Vegetal y de la Interacción Planta-microorganismo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Tissue-specific hormone profiles from woody poplar roots under bending stress

Mechanical forces induced by bending are able to trigger an asymmetrical response in Populus nigra L. woody taproots. This response includes the recruitment of new lateral roots on the convex side and the deposition of reaction wood (RW) on the opposite concave side. Since these responses seem to be induced by asymmetric activity and differentiation of cambium cells, we investigated, in the present work, how mechanical forces could influence the activation of specific phytohormone signaling pathways on the two sides of the vascular cambium. Thus, distinctive tissues were isolated from convex and concave sides of bent poplar root using cryosectioning. Successively, the isolated tissues, represented by the cambial zone, and the developing phloem and xylem, were analyzed using liquid chromatography coupled to tandem mass spectrometry to profile auxins, abscisic acid (ABA), cytokinins (CKs) and their metabolites. The auxin gradient on the concave side, with the IAA maximum localized in the cambium and decreasing level toward the developing phloem and xylem, suggests a pivotal role of IAA in the control of cambial growth rate, xylem differentiation and RW production. The IAA differences between the two bent root sides could be at the basis of the strictly unidirectional RW production. The higher levels of ABA and all CKs metabolites on the concave side support their involvement in RW production, whereby ABA could mediate the adaptation to the deforming conditions generated by bending, while CKs could act in synergy with IAA in controlling cell differentiation and meristem size