LED Color Gradient As A New Screening Tool For Rapid Phenotyping Of Plant Responses To Light Quality

Background The increasing demand for local food production is fueling high interest in the development of controlled environment agriculture. In particular, LED technology brings energy-saving advantages together with the possibility to manipulate plant phenotypes through light quality control. However, optimizing light quality is required for each cultivated plant and specific purpose. Findings In this paper, it is shown that the combination of LED gradient setups with imaging-based non-destructive plant phenotyping constitutes an interesting new screening tool with the potential to improve speed, logistics, and information output. To validate this concept, an experiment was performed to evaluate the effects of a complete range of Red:Blue ratios on seven plant species: Arabidopsis thaliana, Brachypodium distachyon, Euphorbia peplus, Ocimum basilicum, Oryza sativa, Solanum lycopersicum, and Setaria viridis. Plants were exposed during 30 days to the light gradient and showed significant, but species-dependent, responses in terms of dimension, shape, and color. A time series analysis of phenotypic descriptors highlighted growth changes but also transient responses of plant shapes to the Red:Blue ratio. Conclusion This approach, which generated a large reusable dataset, can be adapted for addressing specific needs in crop production or fundamental questions in photobiology.VeLire, Tropical Plant Factory (Plant'HP

Exploring the mechanisms of photoperiod sensing in Brachypodium distachyon

In crops, the proper timing of flowering, which relies on the coordination of exogenous cues with an endogenous developmental program, is crucial to maximize yields. In Brachypodium distachyon, a model temperate grass, the perception of the increasing day lengths of the spring is key to promote the induction of flowering through a complex interplay between the photoperiodic pathway and circadian clock-controlled processes. Here, we summarize the current knowledge of the flowering time control in B. distachyon and describe a mutant allele of the EARLY FLOWERING 3 (ELF3) gene, which was identified through a forward genetic screening for early flowering phenotypes under short day photoperiods. The mutation of elf3 accelerates flowering under most tested photoperiods. This mutant remained sensitive to vernalization but not to changes in the ambient temperature. The early flowering phenotype is corroborated, at the molecular level, with an increase in the expression of genes promoting flowering, the deregulation of the circadian clock rhythms, and the suppression of the expression of the short-day marker FTL9. Finally, to explore the mechanisms through which the photoperiodic pathway regulates flowering, we tested the effect of night breaks and light quality on the induction of flowering in B. distachyon

Heat can erase epigenetic marks of vernalization in Arabidopsis

Vernalization establishes a memory of winter that must be maintained for weeks or months in order to promote flowering the following spring. The stability of the vernalized state varies among plant species and depends on the duration of cold exposure. In Arabidopsis thaliana, winter leads to epigenetic silencing of the floral repressor gene FLOWERING LOCUS C (FLC) and the duration of cold is measured through the dynamics of chromatin modifications during and after cold. The growing conditions encountered post-vernalization are thus critical for the maintenance of the vernalized state. We reported that high temperature leads to devernalization and, consistently, to FLC reactivation in Arabidopsis seedlings. Here we show that the repressive epigenetic mark H3K27me3 decreases at the FLC locus when vernalized seedlings are grown at 30°C, unless they were first exposed to a stabilizing period at 20°C. Ambient temperature thus controls the epigenetic memory of winter

Integrating roots into a whole plant network of flowering time genes in Arabidopsis thaliana

Molecular data concerning the involvement of roots in the genetic pathways regulating floral transition are lacking. In this study, we performed global analyses of the root transcriptome in Arabidopsis in order to identify flowering time genes that are expressed in the roots and genes that are differentially expressed in the roots during the induction of flowering. Data mining of public microarray experiments uncovered that about 200 genes whose mutations are reported to alter flowering time are expressed in the roots (i.e. were detected in more than 50% of the microarrays). However, only a few flowering integrator genes passed the analysis cutoff. Comparison of root transcriptome in short days and during synchronized induction of flowering by a single 22-h long day revealed that 595 genes were differentially expressed. Enrichment analyses of differentially expressed genes in root tissues, gene ontology categories, and cis-regulatory elements converged towards sugar signaling. We concluded that roots are integrated in systemic signaling, whereby carbon supply coordinates growth at the whole plant level during the induction of flowering. This coordination could involve the root circadian clock and cytokinin biosynthesis as a feed forward loop towards the shoot

Molecular analysis of root medium impact on Arabidopsis thaliana development

Hydroponics and soil are the most common media used for plant growth. Hydroponics has the main advantage of providing easy access to the root system and is therefore commonly used for gene expression analyses in molecular studies of the model plant Arabidopsis thaliana. However, the impact of root substrate on plant growth remains poorly documented. Here we show that hydroponics accelerates both shoot growth and developmental phases as compared with culture on soil. In order to identify molecular changes in the roots that could account for these medium effects, a transcriptomic comparison was performed by microarray analysis. This experiment revealed that more than 20% of the genes were differentially expressed in hydroponics vs soil. Among them, the flowering time gene FLOWERING LOCUS C and two clades of microRNA targeted genes. To further assess the role of these genes in roots, artificial microRNAs were designed for root specific expression in transgenic Arabidopsis plants

Flowering Interactive Database [FLOR-ID]

The Flowering Interactive Database [FLOR-ID; http://www.flor-id.org] is an open-access resource that compiles the accumulated knowledge on the regulation of flowering time in the model plant species Arabidopsis thaliana

Perspectives for the update of the Flowering Interactive Database [www.FLOR-ID.org]

The mechanisms controlling the onset of flowering are particularly well documented in Arabidopsis thaliana: hundreds of genes involved in interconnected regulatory networks converge toward the regulation of a few “integrator genes” that ultimately initiate the transition to reproductive development. In 2016, we published a hand-curated interactive database of flowering-time genes (www. or-id.org) that summarizes the knowledge of >1500 articles on this topic. The website includes a set of interactive schemes relying on a list of 306 flowering genes, each of which has a specific detailed webpage describing its function and interactome. Our knowledge of the mechanisms fine-tuning the timing of flowering in Arabidopsis evolves quickly as new articles are published weekly on this topic. Therefore, we think that an update of the FLOR-ID database is timely and would be helpful to the research community