RESUMEN
The cytokinin (CK) phytohormones have long been known to activate cell proliferation in plants. However, how CKs regulate cell division and cell expansion remains unclear. Here, we reveal that a basic helix-loop-helix transcription factor, CYTOKININ-RESPONSIVE GROWTH REGULATOR (CKG), mediates CK-dependent regulation of cell expansion and cell cycle progression in Arabidopsis thaliana. The overexpression of CKG increased cell size in a ploidy-independent manner and promoted entry into the S phase of the cell cycle, especially at the seedling stage. Furthermore, CKG enhanced organ growth in a pleiotropic fashion, from embryogenesis to reproductive stages, particularly of cotyledons. In contrast, ckg loss-of-function mutants exhibited smaller cotyledons. CKG mainly regulates the expression of genes involved in the regulation of the cell cycle including WEE1. We propose that CKG provides a regulatory module that connects cell cycle progression and organ growth to CK responses.
Asunto(s)
Arabidopsis/crecimiento & desarrollo , Arabidopsis/genética , Ciclo Celular/genética , División Celular/genética , Proliferación Celular/genética , Citocininas/genética , Citocininas/metabolismo , Arabidopsis/metabolismo , Regulación de la Expresión Génica de las Plantas , Genes de Plantas , Plantas Modificadas GenéticamenteRESUMEN
We conducted biochemical and physiological experiments to investigate the mode of action of tiafenacil (Terrad'or™), a new protoporphyrinogen IX oxidase (PPO)-inhibiting pyrimidinedione herbicide. Analysis of the half-maximal inhibitory concentration (IC50) against recombinant PPO enzymes from various plant species, including amaranth (Amaranthus tuberculatus), soybean (Glycine max), arabidopsis (Arabidopsis thaliana), and rapeseed (Brassica napus), showed that tiafenacil had an IC50 of 22 to 28â¯nM, similar to the pyrimidinedione herbicides butafenacil and saflufenacil and the N-phenylphthalimide herbicide flumioxazin. By contrast, tiafenacil exhibited 3- to 134-fold lower IC50 values than the diphenyl ether herbicides fomesafen, oxyfluorfen, and acifluorfen. Tiafenacil is non-selective and is herbicidal to both dicots and monocots, such as the weeds velvetleaf (Abutilon theophrasti), amaranth, and barnyardgrass (Echinochloa crus-galli) as well as the crops soybean, rapeseed, rice (Oryza sativa), and maize (Zea mays) at concentrations ranging from 1 to 50⯵M. Treatment of plant tissue with tiafenacil in darkness resulted in the accumulation of protoporphyrin IX. Subsequent exposure to light increased the content of malondialdehyde and significantly decreased the Fv/Fm values of chlorophyll fluorescence. The results suggest that tiafenacil is a new PPO-inhibiting pyrimidinedione herbicide.
Asunto(s)
Herbicidas/farmacología , Magnoliopsida/efectos de los fármacos , Protoporfirinógeno-Oxidasa/antagonistas & inhibidores , Pirimidinonas/farmacología , Magnoliopsida/enzimología , Magnoliopsida/crecimiento & desarrollo , Hojas de la Planta/efectos de los fármacos , Hojas de la Planta/enzimología , Hojas de la Planta/crecimiento & desarrollo , Protoporfirinógeno-Oxidasa/metabolismoRESUMEN
In vascular plants, the xylem network constitutes a complex microfluidic system. The relationship between vascular network architecture and functional hydraulic regulation during actual water flow remains unexplored. Here, we developed a method to visualize individual xylem vessels of the 3D xylem network of Arabidopsis thaliana, and to analyze the functional activities of these vessels using synchrotron X-ray computed tomography with hydrophilic gold nanoparticles as flow tracers. We show how the organization of the xylem network changes dynamically throughout the plant, and reveal how the elementary units of this transport system are organized to ensure both long-distance axial water transport and local lateral water transport. Xylem vessels form distinct clusters that operate as functional units, and the activity of these units, which determines water flow pathways, is modulated not only by varying the number and size of xylem vessels, but also by altering their interconnectivity and spatial arrangement. Based on these findings, we propose a regulatory model of water transport that ensures hydraulic efficiency and safety.
Asunto(s)
Arabidopsis/metabolismo , Agua/metabolismo , Xilema/ultraestructura , Arabidopsis/anatomía & histología , Arabidopsis/ultraestructura , Transporte Biológico , Oro/química , Nanopartículas del Metal/química , Nanopartículas del Metal/ultraestructura , Modelos Biológicos , Sincrotrones , Tomografía Computarizada por Rayos X , Xilema/metabolismoRESUMEN
Our understanding of physical and physiological mechanisms depends on the development of advanced technologies and tools to prove or re-evaluate established theories, and test new hypotheses. Water flow in land plants is a fascinating phenomenon, a vital component of the water cycle, and essential for life on Earth. The cohesion-tension theory (CTT), formulated more than a century ago and based on the physical properties of water, laid the foundation for our understanding of water transport in vascular plants. Numerous experimental tools have since been developed to evaluate various aspects of the CTT, such as the existence of negative hydrostatic pressure. This review focuses on the evolution of the experimental methods used to study water transport in plants, and summarizes the different ways to investigate the diversity of the xylem network structure and sap flow dynamics in various species. As water transport is documented at different scales, from the level of single conduits to entire plants, it is critical that new results be subjected to systematic cross-validation and that findings based on different organs be integrated at the whole-plant level. We also discuss the functional trade-offs between optimizing hydraulic efficiency and maintaining the safety of the entire transport system. Furthermore, we evaluate future directions in sap flow research and highlight the importance of integrating the combined effects of various levels of hydraulic regulation.
Asunto(s)
Plantas/metabolismo , Agua/metabolismo , Xilema/metabolismo , Transporte BiológicoRESUMEN
The phytohormone auxin is a key developmental signal in plants. So far, only auxin perception has been described to trigger the release of transcription factors termed Auxin Response Factors (ARFs) from their auxin/indole-3-acetic acid (AUX/IAA) repressor proteins. Here, we show that phosphorylation of ARF7 and ARF19 by BRASSINOSTEROID-insensitive2 (BIN2) can also potentiate auxin signalling output during lateral root organogenesis. BIN2-mediated phosphorylation of ARF7 and ARF19 suppresses their interaction with AUX/IAAs, and subsequently enhances the transcriptional activity to their target genes lateral organ boundaries-domain16 (LBD16) and LBD29. In this context, BIN2 is under the control of the Tracheary element differentiation inhibitory factor (TDIF)-TDIF receptor (TDR) module. TDIF-initiated TDR signalling directly acts on BIN2-mediated ARF phosphorylation, leading to the regulation of auxin signalling during lateral root development. In summary, this study delineates a TDIF-TDR-BIN2 signalling cascade that controls regulation of ARF and AUX/IAA interaction independent of auxin perception during lateral root development.
Asunto(s)
Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/farmacología , Arabidopsis/crecimiento & desarrollo , Ácidos Indolacéticos/farmacología , Oligopéptidos/farmacología , Raíces de Plantas/crecimiento & desarrollo , Proteínas Quinasas/metabolismo , Factores de Transcripción/metabolismo , Secuencia de Aminoácidos , Arabidopsis/efectos de los fármacos , Arabidopsis/genética , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , ADN de Plantas/metabolismo , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Modelos Biológicos , Datos de Secuencia Molecular , Mutación/genética , Fosforilación/efectos de los fármacos , Raíces de Plantas/efectos de los fármacos , Raíces de Plantas/genética , Unión Proteica/efectos de los fármacos , Unión Proteica/genética , Transducción de Señal , Factores de Transcripción/química , Factores de Transcripción/genética , Transcripción Genética/efectos de los fármacosRESUMEN
Mimosa pudica has three distinct specialized organs, namely, pulvinus, secondary pulvinus, and pulvinule, which are respectively controlling the movements of petioles, leaflets, and pinna in response to external stimuli. Water flow is a key factor for such movements, but detailed studies on the organization of the vascular system for water transport in these organs have not been published yet. In this study, organizations of the xylem vessels and morphological features of the pulvinus, the secondary pulvinus, and the pulvinule were experimentally investigated by X-ray computed tomography and histological technique. Results showed that the xylem vessels were circularly distributed in the specialized motile organs and reorganized into distinct vascular bundles at the extremities. The number and the total cross-sectional area of the xylem vessels were increased inside the specialized motile organs. Morphological characteristics obtained in this study provided new insight to understand the functions of the vascular networks in the dynamic movements of M. pudica.
Asunto(s)
Mimosa/anatomía & histología , Pulvino/anatomía & histología , Xilema/anatomía & histología , Animales , Histocitoquímica , Tomografía Computarizada por Rayos XRESUMEN
Phytohormone brassinosteroids (BRs) play critical roles in plant growth and development. BR acts by modulating the phosphorylation status of two key transcriptional factors, BRI1 EMS SUPPRESSOR1 and BRASSINAZOLE RESISTANT1 (BZR1), through the action of BRASSINOSTEROID INSENSITIVE1/BRI1 ASSOCIATED RECEPTOR KINASE1 receptors and a GSK3 kinase, BRASSINOSTEROID INSENSITIVE2 (BIN2). It is still unknown how the perception of BR at the plasma membrane connects to the expression of BR target genes in the nucleus. We show here that BZR1 functions as a nucleocytoplasmic shuttling protein and GSK3-like kinases induce the nuclear export of BZR1 by modulating BZR1 interaction with the 14-3-3 proteins. BR-activated phosphatase mediates rapid nuclear localization of BZR1. Besides the phosphorylation domain for 14-3-3 binding, another phosphorylation domain in BZR1 is required for the BIN2-induced nuclear export of BZR1. Mutations of putative phosphorylation sites in two distinct domains enhance the nuclear retention of BZR1 and BR responses in transgenic plants. We propose that the spatial redistribution of BZR1 is critical for proper BR signaling in plant growth and development.