Bud outgrowth is a major component of plant architectural plasticity and is influenced by light conditions. While the inhibitory effect of low light intensity on branching is well documented, the underlying regulators remain debated and, especially, the role of sugar availability has never been thoroughly evaluated. Here, we combined experiments with a computational approach quantifying carbon source-sink balance in single-axis rose plants to investigate how continuous and transient light limitation regulate bud outgrowth. Continuous low light reduced photosynthesis, leading to decreased sugar availability and inhibited bud outgrowth. In contrast, a transient period of low light followed by high light unexpectedly stimulated bud outgrowth, shortened the delay between outgrowth of successive buds, and produced an over-branched phenotype. This response resulted from a non-reversible reduction in the growth of apical organs appearing under low light, which lowered carbon demand and caused sugar over-accumulation after the return to high light. Manipulating carbon supply and demand through leaf masking, photosynthetic inhibition, and targeted sucrose feeding supported a causal contribution of sugar availability in these contrasting responses. Beyond these findings, key requirements for models simulating branching plasticity were identified and this work provides a basis for predicting branching responses under fluctuating and complex light environments.

Shoot branching is a key process of plant growth and development, finely controlled by cytokinin and sugars. However, cytokinin fails to induce bud outgrowth in the absence of sugar, and so far nothing is known about its ability to antagonize auxin when sugar availability is limited. Here we demonstrate in rose that cytokinin requires sugar metabolism and signalling to promote bud outgrowth, to down-regulate the expression of RhBRC1, a transcription factor gene that inhibits axillary bud growth, and to antagonize the inhibitory effect of auxin on bud outgrowth. Cytokinin regulation of bud sink strength was tightly associated with sugar metabolism, which was evidenced by the expression of genes involved in sugar metabolism [e.g. glycolysis, the tricarboxylic acid, and the oxidative pentose phosphate pathway (OPPP)], a metabolomic approach, and the quantification of total carbon and nitrogen in buds. Cytokinin supply is associated with a significant up-regulation of the OPPP and nitrogen accumulation. Meanwhile, sugar up-regulated bud sensitivity to cytokinin, associated with a significant down-regulation of the cytokinin signalling regulator RhARR1. These findings highlight the key role of sugar metabolism and signalling in cytokinin-induced bud outgrowth and provide new insights into the importance of nutrient-hormone crosstalk in the regulation of shoot branching.

Ray-tracing models enable the assessment of light quantity and quality intercepted by plant organs, supporting biological studies in growth chambers with varying light conditions. However, their validation within canopies and clear usage methods remain limited. This work establishes a reliable method for using these models. The method includes i) accounting for the intensity and spectrum of light sources in the calibration procedure; ii) a generic calibration strategy using a few well-placed light measurement points based on chamber geometry. It evaluates the method to simulate light phylloclimate at the organ scale across biologically relevant wavebands of contrasted widths and properties. Using the SEC2 light simulation framework, three virtual experiments were conducted in a growth chamber, with and without rose plants. Inputs included chamber geometry, material optical properties, lamp emissions, and digitised plant mock-ups. Simulations were compared with spectral measurements at various chamber positions and sensor orientations, both without plants and inside a canopy. Results showed high accuracy in replicating spatial light variability, with RMSE ranging 0.011 to 0.021 and 0.014-0.038 mu mol m-2s-1nm-1 across different wavebands and sensor orientations, for vertical and horizontal transects, respectively. Applying this approach to a case study demonstrated its effectiveness in formulating new biological hypotheses regarding the role of local light in regulating bud outgrowth. This was achieved by highlighting differences in phylloclimate induced by variations in plant architecture. This work thus provides a comprehensive framework for facilitating the application of ray-tracing models in growth chamber studies.

Photoconversion film technology is one of the solutions to increase food production for the growing global population. This technology optimises the use of the solar spectrum through redirection of the wavelengths toward the most beneficial ones for the plant, such as blue. Previous studies about the effects of blue light on tomatoes have shown a reduction in stem elongation and an increase in plants' defence capacity. This study is a proof of concept of the LitePlus (R) DR Tomato greenhouse foils effects, which enrich the solar spectrum with blue radiation, on tomatoes in comparison to conventional one. Six trials were conducted with two tunnels, each corresponding to a film modality (Blue and Reference) in phytotron. Under each tunnel were placed 30 'Ventero' tomato seedlings from their germination to the 7-8 leaf stage. The growing conditions were precisely controlled at 70% humidity and 22 degrees C/18 degrees C for day/night. Tunnels were placed under plasma lights, which deliver a spectrum close to the solar spectrum, at a light intensity of 250 mu mol m(-2) s(-1) for a 16 h/day photoperiod. The measured variables were non-destructive kinetic variables on phenotypic characteristics, namely tomato plant height, growth rate, and third leaf length of the plants. LitePlus (R) DR Tomato films impact the growth and development of young tomato plants during vegetative phase by reducing growth speed and leaf area, and does not affect the appearance of the flowering. These observations fit very well with the well-described blue LEDS-related effects on young tomato plants.

Axillary bud outgrowth is a major process allowing the plant to adapt its architecture to environmental constraints. Indeed, the dormant buds formed at each leaf axil contain meristems, which depending on the environment, remain quiescent or resume activity leading to bud outgrowth and the development of a new axis [1]. Studies on apical dominance, i.e. the inhibition of buds by the growing apical zone, have highlighted the opposite roles of auxin and sugar, which is involved in a signaling and trophic regulation of bud activity [2-4]. However, understanding the interaction between the environment and the mechanisms of apical dominance is a major issue [3]. Our study tests the long-standing hypothesis that sugar availability is involved in the mediation of light effect on bud outgrowth at plant-level. We combined experimental studies and computer simulations, using rose as a plant model. First, using buds grown in vitro , high sugar availability was demonstrated to reduce auxin repressing effect on bud outgrowth, indicating that it could reduce the auxin-related apical dominance in planta . Sugar effect was highlighted to be due to a repression of a pathway downstream of auxin by testing different possible scenarios in a model [5]. Then, we demonstrated the ability of sugar availability to modulate bud outgrowth rate and to explain, at least partly, light effect in planta . Plants were grown under comfort

Shoot branching is regulated by multiple signals. Previous studies have indicated that sucrose may promote shoot branching through suppressing the inhibitory effect of the hormone strigolactone (SL). However, the molecular mechanisms underlying this effect are unknown. Here, we used molecular and genetic tools to identify the molecular targets underlying the antagonistic interaction between sucrose and SL. We showed that sucrose antagonizes the suppressive action of SL on tillering in rice and on the degradation of D53, a major target of SL signalling. Sucrose inhibits the gene expression of D3, the orthologue of the Arabidopsis F-box MAX2 required for SL signalling. Overexpression of D3 antagonizes sucrose inhibition of D53 degradation and enables the SL inhibition of tillering under high sucrose. Sucrose prevents SL-induced degradation of D14, the SL receptor involved in D53 degradation. In contrast to D3, D14 overexpression enhances D53 protein levels and sucrose-induced tillering, even in the presence of SL. Our results show that sucrose inhibits SL response by affecting key components of SL signalling and, together with previous studies reporting the inhibition of SL synthesis by nitrate and phosphate, demonstrate the central role played by SLs in the regulation of plant architecture by nutrients.

Plants adjust their growth and development through a sophisticated regulatory system integrating endogenous and exogenous cues. Many of them rely on intricate crosstalk between nutrients and hormones, an effective way of coupling nutritional and developmental information and ensuring plant survival. Sugars in their different forms such as sucrose, glucose, fructose and trehalose-6-P and the hormone family of cytokinins (CKs) are major regulators of the shoot and root functioning throughout the plant life cycle. While their individual roles have been extensively investigated, their combined effects have unexpectedly received little attention, resulting in many gaps in current knowledge. The present review provides an overview of the relationship between sugars and CKs signaling in the main developmental transition during the plant lifecycle, including seed development, germination, seedling establishment, root and shoot branching, leaf senescence, and flowering. These new insights highlight the diversity and the complexity of the crosstalk between sugars and CKs and raise several questions that will open onto further investigations of these regulation networks orchestrating plant growth and development.

Shoot branching is a pivotal process during plant growth and development, and is antagonistically orchestrated by auxin and sugars. In contrast to extensive investigations on hormonal regulatory networks, our current knowledge on the role of sugar signalling pathways in bud outgrowth is scarce. Based on a comprehensive stepwise strategy, we investigated the role of glycolysis/the tricarboxylic acid (TCA) cycle and the oxidative pentose phosphate pathway (OPPP) in the control of bud outgrowth. We demonstrated that these pathways are necessary for bud outgrowth promotion upon plant decapitation and in response to sugar availability. They are also targets of the antagonistic crosstalk between auxin and sugar availability. The two pathways act synergistically to down-regulate the expression of BRC1, a conserved inhibitor of shoot branching. Using Rosa calluses stably transformed with GFP-fused promoter sequences of RhBRC1 (pRhBRC1), glycolysis/TCA cycle and the OPPP were found to repress the transcriptional activity of pRhBRC1 cooperatively. Glycolysis/TCA cycle- and OPPP-dependent regulations involve the -1973/-1611 bp and -1206/-709 bp regions of pRhBRC1, respectively. Our findings indicate that glycolysis/TCA cycle and the OPPP are integrative parts of shoot branching control and can link endogenous factors to the developmental programme of bud outgrowth, likely through two distinct mechanisms.

The quality of the sunlight spectrum can be modulated by incorporating optically active formulations into plastic greenhouse covers with the objective to improve plant precocity, yield and fruits' quality.The patented "Light Cascade®" (LC®) technology formulations, which are dispersed in plastic greenhouse films, can induce an increase in the Blue (400-500nm) and in the Red (600-700nm) wavelengths.This study aims to evaluate the effect of the LC® technology on the productivity of two low tunnel cultivated crops, i.e. the Charentais cantaloupe melon and early culture of potato.For each crop, trial campaigns have been performed since 2015 at different experimental and growers' farms in France and Spain.Several LC® formulations have been evaluated and next to their optical properties, the lifetime of the LC® systems was significantly improved.First and/or final cumulated yield (T/ha) of each crop has been quantified and melon fruits' quality has been assessed based on the sugar content quantification and weight.Melon trial results showed a weather conditions and region-specific response underneath the LC® films.The main data indicated (i) an increase of up to 2,2 times yield at the first melon harvest, (ii) an increase of the mean fruit weight (+34,4g) for all harvests and (iii) a stable or an increased sugar content relative to the conventional film.More interestingly, the effect of the LC® greenhouse films on melon production was more pronounced in unfavourable climatic conditions and seems to be temperature dependent.Concerning the early potato crop results, two very interesting results have been observed as (i) an earlier harvest time (8 days) and (ii) an increase of small sized tubers' yield (up to 15%).Further research is ongoing to evaluate the effect of the LC® additives on other greenhouse cultivated crops, such as berries, tomato, pepper, cucumber and cut flowers.Next to this, a better understanding of the temperature effects and light intensity on the performance of the LC® greenhouse films is investigated.

Shoot branching, which is regulated by a complex signalling network, is a major component of plant architecture and therefore of crop yield. Sugars, acting in a network with hormones, have recently emerged as key players in the control of shoot branching. Previous studies in dicotyledonous plants have shown that sucrose suppresses the inhibitory effect of the plant hormone strigolactone (SL) during this process. The molecular mechanisms underlying this effect are unknown. Here we show that sucrose could antagonise the suppressive action of SL on tillering in rice. At the mechanistic level, we revealed that sucrose alleviates SL-mediated degradation of D53. Increase in sucrose availability inhibits the expression of D3, which encodes the orthologue of the arabidopsis F-box MAX2 required for SL signalling. Over-expression of D3 prevented sucrose from inhibiting D53 degradation and enabled the SL inhibition of tillering under high sucrose. The enhanced bud elongation of the d3 mutant to sucrose treatment indicates that suppressed SL perception reduces the minimum amount of sucrose required for sustained bud outgrowth. Decapitation and sugar feeding experiments in pea indicate that RMS4, the D3/MAX2 orthologue in pea, is also involved in the interactions between sucrose and SL. This work shows that D3/MAX2/RMS4 is a key component in the integrating both SL and sugar pathways during the regulation of shoot architecture.

Adaptation of the light spectrum to the greenhouse cultivated crops is considered as one way to improve plant production. Light quality might be increased by the incorporation of optically active light shifting dyes in the greenhouse plastic films which adapt the photosynthetically active radiations (PAR) to photosynthesis and consequently might improve plant growth and yield. This present study aims to evaluate the effects of an increase in the blue (400-500 nm) and in the red (600-700 nm) wavelengths induced by the registered "Light Cascade (R)" technology (LC (R)) on the low and high tunnels cultivated crops i.e., 'Charentais' melon, watermelon, raspberry and early potato. The experiments were performed in different experimental farms and in growers' farms located in France and Spain and qualitative and quantitative parameters were evaluated. The results obtained for the melon and watermelon crops showed globally i) an increase up to 10% of the yield at the first harvests, ii) an increase of the fruit size or weight, and iii) a maintained even increase of the sugar content in comparison to the standard film. It was observed that the effect of the LC (R) is more significant in unfavourable weather conditions (reduced sunlight) on melon. The raspberry showed underneath the LC (R) films an increase of both fruit production at the first harvests and the sugar content. Concerning the early potato crop, the results showed an early harvest time reaching 8 days and an increase of 12% of the final net yield especially for desired small sized tubers. These results suggest that the efficiency of the LC (R) films appeared to be optimal on periods when the sunlight and temperature are insufficient (winter and spring). Further research is ongoing to evaluate the effect of the LC (R) technology on other crops (red fruits, tomato and cut flowers), in relation with additional parameters (temperature regulation, plant disease management and use efficiencies of water and nitrogen).

MAIN CONCLUSION:Specific combinations of physiological and molecular parameters associated with N and S remobilization measured at the onset of flowering were predictive of final crop performances in oilseed rape. Oilseed rape (Brassica napus L.) is a high nitrogen (N) and sulphur (S) demanding crop. Nitrogen- and S-remobilization processes allow N and S requirements to reproductive organs to be satisfied when natural uptake is reduced, thus ensuring high yield and seed quality. The quantification of physiological and molecular indicators of early N and S remobilization could be used as management tools to correct N and S fertilization. However, the major limit of this corrective strategy is to ensure the correlation between final performances-related variables and early measured parameters. In our study, four genotypes of winter oilseed rape (OSR) were grown until seed maturity under four nutritional modalities combining high and/or low N and S supplies. Plant final performances, i.e., seed production, N- and S-harvest indexes, seed N and S use efficiencies, and early parameters related to N- or S-remobilization processes, i.e., photosynthetic leaf area, N and S leaf concentrations, leaf soluble protein and leaf sulphate concentrations, and leaf RuBisCO abundance at flowering, were measured. We demonstrated that contrasting final performances existed according to the N and S supplies. An optimal N:S ratio supply could explain the treatment-specific crop performances, thus justifying N and S concurrent managements. Specific combinations of early measured plant parameters could be used to predict final performances irrespective of the nutritional supply and the genotype. This work demonstrates the potential of physiological and molecular indicators measured at flowering to reflect the functioning of N- and S-compound remobilization and to predict yield and quality penalties. However, because the predictive models are N and S independent, instant N and S leaf analyses are required to further adjust the adequate fertilization. This study is a proof of a concept which opens prospects regarding instant diagnostic tools in the context of N and S mineral fertilization management.

Apical dominance occurs when the growing shoot tip inhibits the outgrowth of axillary buds. Apically-derived auxin in the nodal stem indirectly inhibits bud outgrowth via cytokinins and strigolactones. Recently, sugar deprivation was found to contribute to this phenomenon. Using rose and pea, we investigated whether sugar availability interacts with auxin in bud outgrowth control, and the role of cytokinins and strigolactones, in vitro and in planta. We show that sucrose antagonises auxin's effect on bud outgrowth, in a dose-dependent and coupled manner. Sucrose also suppresses strigolactone inhibition of outgrowth and the rms3 strigolactone-perception mutant is less affected by reducing sucrose supply. However, sucrose does not interfere with the regulation of cytokinin levels by auxin and stimulates outgrowth even with optimal cytokinin supply. These observations were assembled into a computational model in which sucrose represses bud response to strigolactones, largely independently of cytokinin levels. It quantitatively captures our observed dose-dependent sucrose-hormones effects on bud outgrowth and allows us to express outgrowth response to various combinations of auxin and sucrose levels as a simple quantitative law. This study places sugars in the bud outgrowth regulatory network and paves the way for a better understanding of branching plasticity in response to environmental and genotypic factors.

Apical dominance, the process by which the growing apical zone of the shoot inhibits bud outgrowth, involves an intricate network of several signals in the shoot. Auxin originating from plant apical region inhibits bud outgrowth indirectly. This inhibition is in particular mediated by cytokinins and strigolactones, which move from the stem to the bud and that respectively stimulate and repress bud outgrowth. The action of this hormonal network is itself modulated by sugar levels as competition for sugars, caused by the growing apical sugar sink, may deprive buds from sugars and prevents bud outgrowth partly by their signaling role. In this review, we analyze recent findings on the interaction between light, in terms of quantity and quality, and apical dominance regulation. Depending on growth conditions, light may trigger different pathways of the apical dominance regulatory network. Studies pinpoint to the key role of shoot-located cytokinin synthesis for light intensity and abscisic acid synthesis in the bud for R:FR in the regulation of bud outgrowth by light. Our analysis provides three major research lines to get a more comprehensive understanding of light effects on bud outgrowth. This would undoubtedly benefit from the use of computer modeling associated with experimental observations to deal with a regulatory system that involves several interacting signals, feedbacks, and quantitative effects.

Apical dominance, the process by which the growing apical zone of the shoot inhibits bud outgrowth, involves an intricate network of several signals in the shoot. Auxin originating from plant apical region inhibits bud outgrowth indirectly. This inhibition is in particular mediated by cytokinins and strigolactones, which move from the stem to the bud and that respectively stimulate and repress bud outgrowth. The action of this hormonal network is itself modulated by sugar levels as competition for sugars, caused by the growing apical sugar sink, may deprive buds from sugars and prevents bud outgrowth partly by their signaling role. In this review, we analyze recent findings on the interaction between light, in terms of quantity and quality, and apical dominance regulation. Depending on growth conditions, light may trigger different pathways of the apical dominance regulatory network. Studies pinpoint to the key role of shoot-located cytokinin synthesis for light intensity and abscisic acid synthesis in the bud for R:FR in the regulation of bud outgrowth by light. Our analysis provides three major research lines to get a more comprehensive understanding of light effects on bud outgrowth. This would undoubtedly benefit from the use of computer modeling associated with experimental observations to deal with a regulatory system that involves several interacting signals, feedbacks, and quantitative effects.

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.