RESUMEN
An evolutionarily ancient plant hormone receptor complex comprising the α/ß-fold hydrolase receptor KARRIKIN INSENSITIVE 2 (KAI2) and the F-box protein MORE AXILLARY GROWTH 2 (MAX2) mediates a range of developmental responses to smoke-derived butenolides called karrikins (KARs) and to yet elusive endogenous KAI2 ligands (KLs). Degradation of SUPPRESSOR OF MAX2 1 (SMAX1) after ligand perception is considered to be a key step in KAR/KL signaling. However, molecular events which regulate plant development downstream of SMAX1 removal have not been identified. Here we show that Lotus japonicus SMAX1 is specifically degraded in the presence of KAI2 and MAX2 and plays an important role in regulating root and root hair development. smax1 mutants display very short primary roots and elongated root hairs. Their root transcriptome reveals elevated ethylene responses and expression of ACC Synthase 7 (ACS7), which encodes a rate-limiting enzyme in ethylene biosynthesis. smax1 mutants release increased amounts of ethylene and their root phenotype is rescued by treatment with ethylene biosynthesis and signaling inhibitors. KAR treatment induces ACS7 expression in a KAI2-dependent manner and root developmental responses to KAR treatment depend on ethylene signaling. Furthermore, in Arabidopsis, KAR-induced root hair elongation depends on ACS7 Thus, we reveal a connection between KAR/KL and ethylene signaling in which the KAR/KL signaling module (KAI2-MAX2-SMAX1) regulates the biosynthesis of ethylene to fine-tune root and root hair development, which are important for seedling establishment at the beginning of the plant life cycle.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Lotus/metabolismo , Raíces de Plantas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Proteínas Portadoras/metabolismo , Etilenos/biosíntesis , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Germinación/fisiología , Hidrolasas/metabolismo , Péptidos y Proteínas de Señalización Intracelular/genética , Lotus/genética , Liasas/genética , Liasas/metabolismo , Organogénesis de las Plantas/genética , Desarrollo de la Planta/genética , Reguladores del Crecimiento de las Plantas/metabolismo , Plantones/metabolismo , Transducción de Señal/efectos de los fármacosRESUMEN
In rhizobial species that nodulate inverted repeat-lacking clade (IRLC) legumes, such as the interaction between Sinorhizobium meliloti and Medicago, bacteroid differentiation is driven by an endoreduplication event that is induced by host nodule-specific cysteine rich (NCR) antimicrobial peptides and requires the participation of the bacterial protein BacA. We have studied bacteroid differentiation of Sinorhizobium frediiâ HH103 in three host plants: Glycine max, Cajanus cajan and the IRLC legume Glycyrrhiza uralensis. Flow cytometry, microscopy analyses and viability studies of bacteroids as well as confocal microscopy studies carried out in nodules showed that S. fredii HH103 bacteroids, regardless of the host plant, had deoxyribonucleic acid (DNA) contents, cellular sizes and survival rates similar to those of free-living bacteria. Contrary to S. meliloti, S. frediiâ HH103 showed little or no sensitivity to Medicagoâ NCR247 and NCR335 peptides. Inactivation of S. frediiâ HH103 bacA neither affected symbiosis with Glycyrrhiza nor increased bacterial sensitivity to Medicagoâ NCRs. Finally, HH103 bacteroids isolated from Glycyrrhiza, but not those isolated from Cajanus or Glycine, showed an altered lipopolysaccharide. Our studies indicate that, in contrast to the S. meliloti-Medicago model symbiosis, bacteroids in the S. frediiâ HH103-Glycyrrhiza symbiosis do not undergo NCR-induced and bacA-dependent terminal differentiation.
Asunto(s)
Glycyrrhiza uralensis/microbiología , Antígenos O/metabolismo , Nódulos de las Raíces de las Plantas/microbiología , Sinorhizobium fredii/crecimiento & desarrollo , Proteínas Bacterianas/metabolismo , Glycyrrhiza uralensis/genética , Glycyrrhiza uralensis/fisiología , Secuencias Invertidas Repetidas , Lipopolisacáridos/metabolismo , Antígenos O/genética , Nódulos de las Raíces de las Plantas/genética , Nódulos de las Raíces de las Plantas/fisiología , Sinorhizobium fredii/genética , Sinorhizobium fredii/fisiología , SimbiosisRESUMEN
Arbuscular mycorrhiza is an ancient symbiosis between most land plants and fungi of the Glomeromycotina, in which the fungi provide mineral nutrients to the plant in exchange for photosynthetically fixed organic carbon. Strigolactones are important signals promoting this symbiosis, as they are exuded by plant roots into the rhizosphere to stimulate activity of the fungi. In addition, the plant karrikin signaling pathway is required for root colonization. Understanding the molecular mechanisms underpinning root colonization by AM fungi, requires the use of plant mutants as well as treatments with different environmental conditions or signaling compounds in standardized cocultivation systems to allow for reproducible root colonization phenotypes. Here we describe how we set up and quantify arbuscular mycorrhiza in the model plants Lotus japonicus and Brachypodium distachyon under controlled conditions. We illustrate a setup for open pot culture as well as for closed plant tissue culture (PTC) containers, for plant-fungal cocultivation in sterile conditions. Furthermore, we explain how to harvest, store, stain, and image AM roots for phenotyping and quantification of different AM structures.