What are the contributions of cytokinins, abscisic acid and sugars in bud outgrowth regulation by light intensity in rose?

In ornamentals, particularly in rose bush, the visual quality of a plant is an important element of its quality. Bud outgrowth, which is at the origin of branching, strongly impacts plant shape and compactness, that are two traits involved in rosebush visual quality (Boumaza et al. 2009).Changes in the environmental conditions, in particular in light intensity, can impact the number of buds that grow out and change bud outgrowth gradient along a stem in various species, including rose (Leduc et al. 2014; Furet et al. 2014). Bud outgrowth is controlled by a network of interacting hormones, the principal ones are auxin, cytokinins and strigolactones, but the role of abscisic acid is also emerging. Sugars are involved in bud outgrowth regulation too and they interact with the hormonal network. A natural hypothesis is that decreasing light intensity may limit bud outgrowth via a shortage in sugars and changes in plant hormonal content. However, the mechanisms by which light intensity affects bud outgrowth, especiallythe respective role of the different hormones and sugars in this regulation, is still poorly understood.The objective of this work was to test if the control of bud outgrowth gradient along the stem by light intensity is mediated by sugars, cytokinins and/or abscisic acid and to assess which of these actors is the main limiting actor. The study was conducted on whole plants and attention was paid to the location of bud outgrowth along the shoot

Sucrose interacts with auxin in the burst of axillary buds

National audienceResearch focus. Branching is an important process for productivity (number of productive branches) and for visual quality of ornamental plants (branches spatial arrangement). But branching behaviour is difficult to predict due to the lack of knowledge on the all mechanisms regulating the plasticity of the burst of axillary buds. Auxin has an inhibitory action on bud burst and interacts with cytokinins (CKs) and strigolactones (SLs) [1]. Our study focuses on understanding and modelling how a newly-identified player, sugars [2,3], interact with the hormonal network to control bud burst. Methods. Experiments consisted in cultivating nodal stem segments of rosebush in vitro with different sucrose and auxin levels, and in quantifying bud elongation, CK level, and the expression of genes involve in SL biosynthesis and signalling. From these data, we designed and calibrated a computational model accounting for sucrose modulation of bud inhibition by auxin. Results. We observed that increasing sucrose level decreased the inhibition of bud elongation by auxin, so that buds fed with high sucrose level were less inhibited by a given amount of auxin than those fed with low sucrose level. In accordance with literature, auxin repressed CKs and stimulated the expression of SLs biosynthesis genes. We demonstrate that the main effect of sucrose was to repress SL signalling. The model developed from these results reproduced the combined action of sucrose and auxin on bud burst. We validated it for its capacity to predict the effect of external CK supply for different sucrose levels. Conclusions. Our study proposes for the first time a physiological model of the effect of sucrose on bud regulation by auxin at the scale of the bud. Initially observed for rosebush, our results were also validated in pea, demonstrating model genericity. Next step is to understand the role of sugars, together with hormones, in the spatio-temporal regulation of bud burst at the scale of the plant. For that, we will use the computational tool, by coupling our bud model to models simulating sugar and hormone fluxes within a plant architecture

BRANCHED1: A Key Hub of Shoot Branching

Shoot branching is a key process for plant growth and fitness. Newly produced axes result from axillary bud outgrowth, which is at least partly mediated through the regulation of BRANCHED1 gene expression (BRC1/TB1/FC1). BRC1 encodes a pivotal bud-outgrowth-inhibiting transcription factor belonging to the TCP family. As the regulation of BRC1 expression is a hub for many shoot-branching-related mechanisms, it is influenced by endogenous (phytohormones and nutrients) and exogenous (light) inputs, which involve so-far only partly identified molecular networks. This review highlights the central role of BRC1 in shoot branching and its responsiveness to different stimuli, and emphasizes the different knowledge gaps that should be addressed in the near future

Sucrose promotes axillary bud outgrowth in Rosa hybrida and plays a signal role during this process

Shoot branching is a developmental process by which axillary buds are released from dormancy and develop into new axes. Bud outgrowth is largely affected by a number of environmental factors such as temperature, air and soil humidity, gravitropism and light, confering thus plasticity to the plant development. Control of bud outgrowth is thereby a key mechanism in the establishment of plant architecture in response to environment. Sugars, whose levels in plant are also highly dependent on the environment, have recently been shown to be implicated during bud outgrowth in Rosa hybrida. To test the impact of different sucrose levels on bud outgrowth, excised buds have been in vitro cultivated on MS media containing different sucrose concentrations. We then tested the impact of different non-metabolizable sucrose analogs to put in evidence a potential sucrose-signaling pathway in this process. Our results revealed that sucrose levels modulated bud outgrowth and that this dissacharide could also play a signal role during this event. Moreover, increasing sucrose supply to in vitro cultivated buds released the inhibitory effect of auxin on bud outgrowth, putting for the first time in evidence an antagonsim between this nutrient and this hormone. Further analysis revealed that the polarization of the auxin transport between bud and stem, which is a prerequisite to allow bud to grow out, is a target of the antagonism between sucrose and auxin. This work proposes a model that integrates sucrose as an endogenous signal in the complex network that regulates bud outgrowth in response to environmen

Molecular Characterisation of the Sucrose Transporter HbSUT1B in Relation to Rubber Production in Latex Cells

The rubber synthesis in latex cells requires sucrose. These particular cells are heterotrophic ones and are apoplastically connected to other tissues. Such features imply that the rubber yield may depend on the latex cell efficiency to absorb and to use the imported sucrose. This study investigates the sucrose transporters as key genes for rubber biosynthesis involved in the ethylene-stimulated rubber yield. Seven putative sucrose transporters had been isolated from a latex-derived cDNA library of PB 217. Expression profiling of these sucrose transporters under ethylene stimulation in PB 217 underlined the role of one sucrose transporter: HbSUT1B (Hevea brasiliensis Sucrose Transporter 6) (Dusotoit-Coucaud et al., 2007). This paper reports the next stage in HbSUT1B, molecular characterisation. Its expression in different parts of the rubber tree was studied. It was preferentially expressed in leaves and bark. This result was completed by in-situ hybridisation experiments. In addition, promoter cloning and analysis revealed some clues for the wounding regulation of HbSUT1B. The HbSUT1B expression was analysed in response to different treatments in latex or bark tissues. HbSUT1B was considerably up-regulated by hormones and wounding in bark but not in latex. This regulation appeared to be tissue-specific

Caractérisation du transporteur de saccharose HbSUT6 des cellules laticifères chez Hevea brasiliensis

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The PUF Protein Family: Overview on PUF RNA Targets, Biological Functions, and Post Transcriptional Regulation

Post-transcriptional regulation of gene expression plays a crucial role in many processes. In cells, it is mediated by diverse RNA-binding proteins. These proteins can influence mRNA stability, translation, and localization. The PUF protein family (Pumilio and FBF) is composed of RNA-binding proteins highly conserved among most eukaryotic organisms. Previous investigations indicated that they could be involved in many processes by binding corresponding motifs in the 3UTR or by interacting with other proteins. To date, most of the investigations on PUF proteins have been focused on Caenorhabditis elegans, Drosophila melanogaster, and Saccharomyces cerevisiae, while only a few have been conducted on Arabidopsis thaliana. The present article provides an overview of the PUF protein family. It addresses their RNA-binding motifs, biological functions, and post-transcriptional control mechanisms in Caenorhabditis elegans, Drosophila melanogaster, Saccharomyces cerevisiae, and Arabidopsis thaliana. These items of knowledge open onto new investigations into the relevance of PUF proteins in specific plant developmental processes