Franck Anicet Ditengou

• Ph. D.
• Head of the Bio Imaging Core Light Microscopy (BiMiC) at University of Freiburg

Lateral roots are initiated postembryonically in response to environmental cues, enabling plants to explore efficiently their underground environment. However, the mechanisms by which the environment determines the position of lateral root formation are unknown. In this study, we demonstrate that in Arabidopsis thaliana lateral root initiation can...

The mutualistic association of roots with ectomycorrhizal fungi promotes plant health and is a hallmark of boreal and temperate forests worldwide. In the pre-colonization phase, before direct contact, lateral root (LR) production is massively stimulated, yet little is known about the signals exchanged during this step. Here, we identify sesquiterpe...

The early phase of the interaction between tree roots and ectomycorrhizal fungi, prior to symbiosis establishment, is accompanied by a stimulation of lateral root (LR) development. We aimed to identify gene networks that regulate LR development during the early signal exchanges between poplar (Populus tremula x Populus alba) and the ectomycorrhizal...

Active polar transport establishes directional auxin flow and the generation of local auxin gradients implicated in plant responses and development. Auxin modulates gravitropism at the root tip and root hair morphogenesis at the differentiation zone. Genetic and biochemical analyses provide evidence for defective basipetal auxin transport in trh1 r...

Local efflux-dependent auxin gradients and maxima mediate organ and tissue development in plants. Auxin efflux is regulated by dynamic expression and subcellular localization of the PIN auxin-efflux proteins, which appears to be established not only through a self-organizing auxin-mediated polarization mechanism, but also through other means, such...

The continuous growth of roots depends on their ability to maintain a balanced ratio between cell production and cell differentiation at the tip. This process is regulated by the hormonal balance of cytokinin and auxin. However, other important regulators, such as plant folates, also play a regulatory role. In this study, we investigated the impact...

CLIC5 belongs to a family of ion channels with six members reported so far. In vertebrates, the CLIC5 gene encodes two different isoforms, CLIC5A and CLIC5B. In addition to its ion channel activity, there is evidence for further functions of CLIC5A, such as the remodeling of the actin cytoskeleton during the formation of a functional glomerulus in...

The continuous growth of roots depends on their ability to maintain a balanced ratio between cell production and cell differentiation at the tip. This process was reported to be regulated by the hormonal balance of cytokinin and auxin. However, other important regulators, such as plant folates, have also been reported to play a regulatory role. In...

During root nodule symbiosis (RNS), cell-division activity is re-initiated and sustained in the root cortex to create a hospitable cellular niche. Such temporary and spatially confined site is required to render host cells compatible with the intracellular progression of rhizobia. Although it has been suggested that early infection events might inv...

During root nodule symbiosis (RNS), cell-division activity is re-initiated and sustained in the root cortex to create a hospitable cellular niche. Such temporary and spatially confined site is required to render host cells compatible with the intracellular progression of rhizobia. Although it has been suggested that early infection events might inv...

During root nodule symbiosis (RNS), cell-division activity is re-initiated and sustained in the root cortex to create a hospitable cellular niche. Such temporary and spatially confined site is required to render host cells compatible with the intracellular progression of rhizobia. Although it has been suggested that early infection events might inv...

An environmentally responsive root system is crucial for plant growth and crop yield, especially in suboptimal soil conditions. This responsiveness enables the plant to exploit regions of high nutrient density while simultaneously minimizing abiotic stress. Despite the vital importance of root systems in regulating plant growth, significant gaps of...

In contrast to other eukaryotic model organisms, the closely related ubiquitin (Ub)-conjugating enzymes UBC35 and UBC36 are the main sources of K63-linked Ub chains in Arabidopsis.1 Although K63-linked chains have been associated with the regulation of vesicle trafficking, definitive proof for their role in endocytosis was missing. We show that the...

Legumes have maintained the ability to associate with rhizobia to sustain the nitrogen-fixing root nodule symbiosis (RNS). In Medicago truncatula, the Nod factor (NF)-dependent intracellular root colonization by Sinorhizobium meliloti initiates from young, growing root hairs. They form rhizobial traps by physically curling around the symbiont.1,2 A...

Rhizobial infection of legume roots during the development of nitrogen fixing root nodules can occur intracellularly, through plant-derived infection threads traversing cells, or intercellularly, via bacterial entry between epidermal plant cells. Although it is estimated that around 25% of all legume genera are intercellularly infected, the pathway...

During the immune response, activation of the secretory pathway is key to mounting an effective response, while gauging its output is important to maintain cellular homeostasis. The Exo70 subunit of the exocyst functions as a spatiotemporal regulator by mediating numerous interactions with proteins and lipids. However, a molecular understanding of...

Highlight Our data suggest a model that defines the capacity of incipient leaf vascular cells to develop based on the relative strength of both auxin biosynthesis and auxin transport. Abstract Our current understanding of vein development in leaves is based on canalization of the plant hormone auxin into self-reinforcing streams which determine the...

Plant cell infections are tightly orchestrated by cell wall (CW) alterations, plasma membrane (PM) resident signalling processes and dynamic remodelling of the cytoskeleton. During root nodule symbiosis these processes result in morpho-dynamic responses including root hair swelling and curling, PM invagination and polar growth of a tubular infectio...

Rhizobial infection of legume roots during development of nitrogen fixing root nodules occurs either intracellularly though plant derived infection threads traversing the epidermal and cortical cell layers to deliver the bacteria or intercellularly via bacterial entry between epidermal plant cells. Although, around 25% of all legume genera are post...

Exquisitely regulated plastid-to-nucleus communication by retrograde signaling pathways is essential for fine-tuning of responses to the prevailing environmental conditions. The plastidial retrograde signaling metabolite methylerythritol cyclodiphosphate (MEcPP) has emerged as a stress signal transduced into a diverse ensemble of response outputs....

The initiation of intracellular host cell colonization by symbiotic rhizobia in Medicago truncatula requires repolarization of root hairs, which includes the re-arrangement of cytoskeletal filaments. The molecular players governing microtubule (MT) re-organization during rhizobial infections remain to be discovered. Here, we identified M. truncatul...

Exquisitely regulated plastid-to-nucleus communication by retrograde signaling pathways is essential for fine-tuning of responses to the prevailing environmental conditions. The plastidial retrograde signaling metabolite methylerythritol cyclodiphosphate (MEcPP) has emerged as a stress signal transduced into a diverse ensemble of response outputs....

Plants orientate their growth either towards (in roots) or away from (in shoots) the Earth’s gravitational field. While we are now starting to understand the molecular architecture of these gravity response pathways, the gravity receptor remains elusive. This perspective looks at the biology of statoliths and suggests it is conceivable that their i...

The initiation of intracellular host cell colonization by symbiotic rhizobia in Medicago truncatula requires repolarization of root hairs, which includes the re-arrangement of cytoskeletal filaments. The molecular players governing microtubule (MT) re-organization during infection remain to be discovered. Here, we identified the M. truncatula DREPP...

Plant growth flexibly adapts to environmental conditions. Growth initiation itself may be conditional to a suitable environment, while the most common response of plants to adverse conditions is growth inhibition. Most of our understanding about environmental growth inhibition comes from studies on various plant hormones, while less is known about...

The exocyst is a conserved hetero-octameric complex that mediates early tethering of post-Golgi vesicles during exocytosis. Its Exo70 subunit functions as a spatiotemporal regulator by mediating numerous interactions with proteins and lipids. However, a molecular understanding of the exocyst functions remains challenging. Exo70B2 localized to dynam...

Plants respond to gravitational force through directional growth along the gravity vector. Although auxin is the central component of the root graviresponse, it works in concert with other plant hormones. Here, we show that the folate precursor para-aminobenzoic acid (PABA) is a key modulator of the auxin-ethylene interplay during root gravitropism...

The pervasive influence of gravity on life on Earth presents barriers to our identifying and understanding of the signaling pathways which have evolved in response to it. Plants are at the same time positively and negatively gravitropic, using the Earth’s gravity to define their stature both above and below ground. Here we review some of the signal...

Large-scale methods and robust algorithms are needed for a quantitative analysis of cells status/geometry in situ. It allows the understanding the cellular mechanisms that direct organ growth in response to internal and environmental cues. Using advanced whole-stack imaging in combination with pattern analysis, we have developed a new approach to i...

The ancient morphoregulatory hormone auxin dynamically realigns dedicated cellular processes that shape plant growth under prevailing environmental conditions. However, the nature of the stress-responsive signal altering auxin homeostasis remains elusive. Here we establish that the evolutionarily conserved plastidial retrograde signaling metabolite...

The development of leaf primordia is subject to light control of meristematic activity. Light regulates the expression of thousands of genes with roles in cell proliferation, organ development and differentiation of photosynthetic cells. Previous work has highlighted roles for hormone homeostasis and the energy-dependent TOR kinase in meristematic...

Auxin gradients are sustained by series of influx and efflux carriers whose subcellular localization is sensitive to both exogenous and endogenous factors. Recently the localization of the Arabidopsis thaliana auxin efflux carrier PIN ‐ FORMED ( PIN ) 6 was reported to be tissue‐specific and regulated through unknown mechanisms. Here, we used genet...

Plant growth flexibly adapts to environmental conditions, implying cross-talk between environmental signalling and developmental regulation. Here, we show that the PIN auxin efflux carrier family possesses three highly conserved putative mitogen-activated protein kinase (MAPK) sites adjacent to the phosphorylation sites of the well-characterised AG...

The plant hormone auxin (indole-3-acetic acid, IAA) has a profound influence over plant cell growth and differentiation. Current understanding of vein development in leaves is based on the canalization of auxin into self-reinforcing streams which determine the sites of vascular cell differentiation. However, the role of auxin biosynthesis during le...

Plant roots are among most intensively studied biological systems in gravity research. Altered gravity induces asymmetric cell growth leading to root bending. Differential distribution of the phytohormone auxin underlies root's responses to gravity being coordinated by auxin efflux transporters from the PIN family. The objective of this study was t...

Ground-based simulators of microgravity such as fast rotating 2-D clinostats are valuable tools to study gravity related processes. We describe here a versatile g-value-adjustable 2-D clinostat that is suitable for plant analysis. To avoid seedling adaptation to 1 g after clinorotation, we designed chambers that allow rapid fixation. A detailed pro...

Understanding the mechanisms through which cells perceive and respond to gravity is of fundamental relevance to space biology. In plants altered gravity induces asymmetric cell growth leading to root bending. This process depends on the differential distribution of the phytohormone auxin which is regulated by auxin efflux transporters. The objectiv...

Ground-based simulators of microgravity such as fast rotating 2-D clinostats are valuable tools to study gravity related processes. We describe here a versatile g-value-adjustable 2-D clinostat that is suitable for plant analysis. To avoid seedling adaptation to 1 g after clinorotation, we designed chambers that allow rapid fixation. A detailed pro...

To achieve a detailed understanding of processes in biological systems, cellular features must be quantified in the three-dimensional (3D) context of cells and organs. We introduce the intrinsic Root Coordinate System (iRoCS) as a reference model for the root apical meristem (RAM) of plants. iRoCS enables direct and quantitative comparison between...

Plant roots are among most intensively studied biological systems in gravity research. Altered gravity induces asymmetric cell growth leading to root bending. Differential distribution of the phytohormone auxin underlies root responses to gravity, being coordinated by auxin efflux transporters from the PIN family. The objective of this study was to...

Glutathione is involved in thiol redox signaling and acts as a major redox buffer against reactive oxygen species, helping to maintain a reducing environment in vivo. Glutathione reductase (GR) catalyzes the reduction of glutathione disulfide (GSSG) into reduced glutathione (GSH). The Arabidopsis thaliana genome encodes two GRs: GR1 and GR2. Wherea...

Leaves are produced postembryonically at the flanks of the shoot apical meristem. Their initiation is induced by a positive feedback loop between auxin and its transporter PIN1. The expression and polarity of PIN1 in the shoot apical meristem is thought to be regulated primarily by auxin concentration and flow. The formation of an auxin maximum in...

Land plants are characterised by haplo-diploid life cycles, and developing ovules are the organs in which the haploid and diploid generations coexist. Recently it has been shown that hormones such as auxin and cytokinins play important roles in ovule development and patterning. The establishment and regulation of auxin levels in cells is predominan...

PIN2, PIN4, PIN5, PIN6 and PIN7 are not expressed in developing ovules. (A) a PIN2:PIN2-GFP ovule at stage 2–IV and a primary root (B); (C) a PIN4:GUS ovule at stage 2–III and a primary root (D); (E) in situ hybridisation to developing ovules (stage 2–III) using an antisense PIN5 probe, and to developing stamens and carpel leaves (F). (G) a PIN6:GU...

pDEH9 is an ovule-specific promoter also in Arabidopsis thaliana. The Antirrhinum majus DEF9 promoter (pDEH9) drives reporter gene expression (GUS) only in developing ovules, the promoter being active from stage II (A) to stage 3–V (E). fg, female gametophyte; ii, inner integument; oi, outer integument; fun, funiculus; nu, nucellus. (TIF)

A Analysis of pin1-5 developing ovules. 20 pistils collected from 4 independent plants have been analysed. B and C Analysis of T2 pDEFH9:amiPIN1 and pDEFH9:amiPIN1-3 plants. The total number of ovules and the percentage of ovule abortion are reported. 5 siliques per individual were observed, and 15 independent lines have been analysed. Aberrant emb...

Ovule development and the auxin response. (A,C) Confocal analysis of wild-type ovules, (B,D) DR5rev:3XVENUS-N7 ovules at the corresponding stages. In C and D the endothelium begins to develop (see arrow) whereas the nucellar cells degenerate and accordingly the fluorescent nuclear auxin response is no longer detectable, though the auxin response is...

YUC4 is expressed in developing ovules. The YUC4 promoter (pYUC4) does not drive reporter gene expression (GUS) in developing ovules between stages 1–I (A) and 3–I (C). Reporter gene activity begins to be detected in ovules at stage 3–II (D) and it is maintained until stage 3–V (E). fg, female gametophyte; ii, inner integument; oi, outer integument...

PIN1 expression in pDEFH9:amiPIN1 flowers. Real-time PCR to evaluate PIN1 expression in pDEFH9:amiPIN1 flowers. Two pairs of PIN1 specific primers were employed (orange and green). (TIF)

The auxin response in normal and mutated ovules of pDEFH9:amiPIN1 plants. (A) The DR5rev:GFP promoter is active in mutated ovules unable to complete megagametogenesis. fg, female gametophyte; ii, inner integument; oi, outer integument; fun, funiculus; nu, nucellus Scale bars: 20 µm. (TIF)

Sequences of oligonucleotide primers used in this work. (DOCX)

MicroRNAs (miRNAs) affect fundamental processes of development. In plants miRNAs regulate organ development, transition to flowering, and responses to abiotic/biotic stresses. To understand the biological role of miRNAs, besides identifying their targeted transcripts, it is necessary to characterise the spatio-temporal regulation of their expressio...

Local, efflux-dependent auxin gradients and maxima mediate organ and tissue development in plants. The auxin-efflux pattern is regulated by dynamic expression and asymmetric subcellular localization of PIN auxin-efflux proteins during plant organogenesis. Thus, the question of how the expression and subcellular localization of PIN proteins are cont...

Semiconductor nanocrystals are used in applications as diverse as solar‐energy conversion, lighting, displays and biological imaging. While electrons and holes move freely in bulk semiconductors, they ‘recombine’ and emit light when they are confined in a quantum dot or nanocrystal. Moreover, as the color of this light can be tuned by varying the...

Lateral root (LR) stimulation during early signal exchange between plant roots and ectomycorrhizal (ECM) fungi has recently been shown to be achieved by modulation of auxin gradients. We suggested that this modulation could occur through altered polar auxin transport (PAT) and through activation of auxin signalling pathways in the root. However, it...

The storage and mobilization of nutrients in wood and bark tissues is a typical feature of trees. Sulfur can be stored as sulfate, which is transported from source to sink tissues through the phloem. In the present study two transcripts encoding sulfate transporters (SULTR) were identified in the phloem of grey poplar (Populus tremula x P. alba). T...

Gravity plays a fundamental role in plant growth and development. Up to now, little is known about the molecular organisation of the signal transduction cascades and networks which co-ordinate gravity perception and response. By using an integrated systems biological approach, a systems analysis of gravity perception and the subsequent tightly-regu...

The bilateral symmetry of a dicotyledon embryo is tightly associated with the directional flow of auxin. Disruption of polar auxin flow results in various developmental abnormalities. The pct1-2 mutant of tomato, showing polycotyledony, also has enhanced polar auxin transport in hypocotyls. Immunocytochemical analysis revealed increased PIN1 protei...

In plants, Rop/Rac GTPases have emerged as central regulators of diverse signalling pathways in plant growth and pathogen defence. When active, they interact with a wide range of downstream effectors. Using yeast two-hybrid screening we have found three previously uncharacterized receptor-like protein kinases to be Rop GTPase-interacting molecules:...

The regulation of plant growth responds to many stimuli. These responses allow environmental adaptation, thereby increasing fitness. In many cases, the relay of information about a plant's environment is through plant hormones. These messengers integrate environmental information into developmental pathways to determine plant shape. This review wil...

Luminescence color multiplexing is one of the most intriguing benefits, which might occur by using semiconductor Quantum Dots (QDs) as labels for biomolecules. It was found, that the luminescence of QDs can be quenched, and replaced by a luminescence peak at approximately 460 nm on hybridization with certain regions of Arabidopsis thaliana tissue....

Lys-63-linked multiubiquitin chains play important roles in signal transduction in yeast and in mammals, but the functions for this type of chain in plants remain to be defined. The RING domain protein RGLG2 (for RING domain Ligase2) from Arabidopsis thaliana can be N-terminally myristoylated and localizes to the plasma membrane. It can form Lys-63...

Gravity is a fundamental factor which affects all living organisms. Plant development is well adapted to gravity by directing roots downward and shoots upwards. For more than a century, plant biologists have been fascinated to describe the molecular mechanisms underlying the gravitropic response of plants. Important progress towards signal percepti...

In multicellular organisms, patterning is a process that generates axes in the primary body plan, creates domains upon organ formation, and finally leads to differentiation into tissues and cell types. We identified the Arabidopsis thaliana TORNADO1 (TRN1) and TRN2 genes and their role in leaf patterning processes such as lamina venation, symmetry,...

Since 1995 the role of fungal hypaphorine in plants has been widely investigated and its IAA-antagonist activity recog-nized. Evidence of competitive antagonism includes organ development, gene expression or molecule–molecule interac-tion levels. Based on present knowledge, three sites of hypa-phorine/IAA competition and subsequent signalling pathw...

The plant hormone auxin has long been known to play a crucial role in plant growth and development, but how it affects so many different processes has remained a mystery. Recent evidence from genetic and molecular studies has begun to reveal a possible mechanism for auxin action. In this article we will present an overview with specific emphasis on...

The indole alkaloids brucine and yohimbine, just like hypaphorine, counteract indole-3-acetic acid (IAA) activity in seedling roots, root hairs and shoots, but do not appear to alter auxin transport in roots or in cultured cells. In roots, the interactions between IAA and these three alkaloids appear competitive and specific since these molecules i...

Hypaphorine, an indole alkaloid from the ectomycorrhizal fungus Pisolithus tinctorius Coker & Couch., counteracts indole-3-acetic acid (IAA) activity and controls the rate of root hair elongation in Eucalyptus globulus ssp. bicostata. The present investigation shows that hypaphorine changes cytoskeletal organisation in elongating root hairs of the...

Development of ectomycorrhizas involves multiple genes that are implicated in a complex series of interdependent, sequential steps. Current research into ectomycorrhiza development and functioning is aimed at understanding this plant–microbe interaction in a framework of the developmental and physiological processes that underlie colonization and m...

The mode of interaction between indole-3-acetic acid and hypaphorine (tryptophan betaine), a putative auxin antagonist isolated from Ectomycorrizal fungi, during the IAA-dependent inhibition of the tap root elongation in Eucalyptus seedlings were analyzed with the in vivo Lineweaver-Burk kinetic analysis, and determined to be a competitive interact...

Hypaphorine, the major indolic compound isolated from the ectomycorrhizal fungus Pisolithus tinctorius, controls the elongation rate of root hairs. At inhibitory concentrations (100 μM), hypaphorine induced a transitory swelling of root hair tips of Eucalyptus globulus Labill. ssp. bicostata. When the polar tip growth resumed, a characteristic defo...

Very little is known about the molecules regulating the interaction between plants and ectomycorrhizal fungi during root colonization. The role of fungal auxin in ectomycorrhiza has repeatedly been suggested and questioned, suggesting that, if fungal auxin controls some steps of colonized root development, its activity might be tightly controlled i...

La mise en place de la symbiose mycorhizienne implique l'établissement d'un dialogue entre deux partenaires, une plante et un champignon. Cette communication se fait par l'intermédiaire de molécules signal. La synthèse et l'accumulation d'hypaphorine (un alcaloïde indolique) dans les hyphes de Pisolithus tinctorius colonisant les racines d'Eucalypt...

A full-length cDNA coding for a symbiosis-regulated transcript, EgHypar, was isolated by differential screening from a Eucalyptus globulus bicostata–Pisolithus tinctorius ectomycorrhiza. The sequence of this clone revealed a protein with an estimated molecular mass of 25.5 kDa that exhibited a high degree of homology (66%) with plant auxin-induced...