Molecular mechanisms of shade tolerance in plants.

Shade tolerance is an ecological concept used in a wide range of disciplines, from plant physiology to landscaping or gardening. It refers to the strategy of some plants to persist and even thrive in environments with low light levels because of the shade produced by the vegetation proximity (e.g.

Development and carotenoid synthesis in dark-grown carrot taproots require PHYTOCHROME RAPIDLY REGULATED1.

Light stimulates carotenoid synthesis in plants during photomorphogenesis through the expression of PHYTOENE SYNTHASE (PSY), a key gene in carotenoid biosynthesis. The orange carrot (Daucus carota) synthesizes and accumulates high amounts of carotenoids in the taproot that grows underground. Contrary to other organs, light impairs carrot taproot development and represses the expression of carotenogenic genes, such as DcPSY1 and DcPSY2, reducing carotenoid accumulation.

Effect of light intensity on steviol glycosides production in leaves of Stevia rebaudiana plants.

Stevia rebaudiana leaf extracts contain stevioside and rebaudioside A, two steviol glycosides (SGs) used as natural sweeteners because of their non-toxic, thermally stable and non-caloric properties. Indeed, leaf extracts can be up to 300 times sweeter than sucrose. Stevioside and rebaudioside A have organoleptic differences, the first one having an undesirable bitterness and the second one a higher sweetener capacity.

Light signals generated by vegetation shade facilitate acclimation to low light in shade-avoider plants.

When growing in search for light, plants can experience continuous or occasional shading by other plants. Plant proximity causes a decrease in the ratio of R to far-red light (low R:FR) due to the preferential absorbance of R light and reflection of FR light by photosynthetic tissues of neighboring plants. This signal is often perceived before actual shading causes a reduction in photosynthetically active radiation (low PAR).

Adjustment of the PIF7-HFR1 transcriptional module activity controls plant shade adaptation.

Shade caused by the proximity of neighboring vegetation triggers a set of acclimation responses to either avoid or tolerate shade. Comparative analyses between the shade-avoider Arabidopsis thaliana and the shade-tolerant Cardamine hirsuta revealed a role for the atypical basic-helix-loop-helix LONG HYPOCOTYL IN FR 1 (HFR1) in maintaining the shade tolerance in C. hirsuta, inhibiting hypocotyl elongation in shade and constraining expression profile of shade-induced genes.

The International Symposium on Plant Photobiology 2019: a bright and colourful experience.

Light is a key resource for plants as it fuels photosynthesis. It also provides essential information about their habitat. Thus, light tracking is of great importance to plants throughout their life cycle.

Shedding light on the chromatin changes that modulate shade responses.

Perception of vegetation proximity or plant shade informs of potential competition for resources by the neighboring vegetation. As vegetation proximity impacts on both light quantity and quality, perception of this cue by plant photoreceptors reprograms development to result in responses that allow plants to compete with the neighboring vegetation. Developmental reprogramming involves massive and rapid changes in gene expression, with the concerted action of photoreceptors and downstream transcription factors.

Photoreceptor Activity Contributes to Contrasting Responses to Shade in Cardamine and Arabidopsis Seedlings.

Plants have evolved two major ways to deal with nearby vegetation or shade: avoidance and tolerance. Moreover, some plants respond to shade in different ways; for example, Arabidopsis () undergoes an avoidance response to shade produced by vegetation, but its close relative tolerates shade. How plants adopt opposite strategies to respond to the same environmental challenge is unknown.

Shade Avoidance and Neighbor Detection.

Plants detect neighboring vegetation as potential competitors for resources. Vegetation proximity is perceived by changes in the red (R) to far-red (FR) ratio (R:FR) through the phytochrome photoreceptors. To face this challenge, many plants have evolved the strategy to avoid shade, displaying a series of responses known as the shade avoidance syndrome (SAS).

Chloroplasts Modulate Elongation Responses to Canopy Shade by Retrograde Pathways Involving HY5 and Abscisic Acid.

Plants use light as energy for photosynthesis but also as a signal of competing vegetation. Using different concentrations of norflurazon and lincomycin, we found that the response to canopy shade in Arabidopsis () was repressed even when inhibitors only caused a modest reduction in the level of photosynthetic pigments. High inhibitor concentrations resulted in albino seedlings that were unable to elongate when exposed to shade, in part due to attenuated light perception and signaling via phytochrome B and phytochrome-interacting factors.

A non-DNA-binding activity for the ATHB4 transcription factor in the control of vegetation proximity.

In plants, perception of vegetation proximity by phytochrome photoreceptors activates a transcriptional network that implements a set of responses to adapt to plant competition, including elongation of stems or hypocotyls. In Arabidopsis thaliana, the homeodomain-leucine zipper (HD-Zip) transcription factor ARABIDOPSIS THALIANA HOMEOBOX 4 (ATHB4) regulates this and other responses, such as leaf polarity. To better understand the shade regulatory transcriptional network, we have carried out structure-function analyses of ATHB4 by overexpressing a series of truncated and mutated forms and analyzing three different responses: hypocotyl response to shade, transcriptional activity and leaf polarity.

Illuminating colors: regulation of carotenoid biosynthesis and accumulation by light.

Light stimulates the biosynthesis of carotenoids and regulates the development of plastid structures to accommodate these photoprotective pigments. Work with Arabidopsis revealed molecular factors coordinating carotenoid biosynthesis and storage with photosynthetic development during deetiolation, when underground seedlings emerge to the light. Some of these factors also adjust carotenoid biosynthesis in response to plant proximity (i.

Approaches to Study Light Effects on Brassinosteroid Sensitivity.

Light perception and hormone signaling in plants are likely connected at multiple points. Light conditions, perceived by photoreceptors, control plant responses by altering hormone concentration, tissue sensitivity, or a combination of both. Whereas it is relatively straightforward to assess the light effects on hormone levels, hormone sensitivity is subjected to interpretation.

DRACULA2 is a dynamic nucleoporin with a role in regulating the shade avoidance syndrome in Arabidopsis.

When plants grow in close proximity basic resources such as light can become limiting. Under such conditions plants respond to anticipate and/or adapt to the light shortage, a process known as the shade avoidance syndrome (SAS). Following genetic screening using a shade-responsive luciferase reporter line (PHYB:LUC), we identified DRACULA2 (DRA2), which encodes an Arabidopsis homolog of mammalian nucleoporin 98, a component of the nuclear pore complex (NPC).

Plant Responses to Vegetation Proximity: A Whole Life Avoiding Shade.

In high density of vegetation, plants detect neighbors by perceiving changes in light quality through phytochrome photoreceptors. Close vegetation proximity might result in competition for resources, such as light. To face this challenge, plants have evolved two alternative strategies: to either tolerate or avoid shade.

Meta-Analysis of Arabidopsis KANADI1 Direct Target Genes Identifies a Basic Growth-Promoting Module Acting Upstream of Hormonal Signaling Pathways.

An intricate network of antagonistically acting transcription factors mediates the formation of a flat leaf lamina of Arabidopsis (Arabidopsis thaliana) plants. In this context, members of the class III homeodomain leucine zipper (HD-ZIPIII) transcription factor family specify the adaxial domain (future upper side) of the leaf, while antagonistically acting KANADI transcription factors determine the abaxial domain (future lower side). Here, we used a messenger RNA sequencing approach to identify genes regulated by KANADI1 (KAN1) and subsequently performed a meta-analysis combining our data sets with published genome-wide data sets.

The shade avoidance syndrome in Arabidopsis: the antagonistic role of phytochrome a and B differentiates vegetation proximity and canopy shade.

Light limitation caused by dense vegetation is one of the greatest threats to plant survival in natural environments. Plants detect such neighboring vegetation as a reduction in the red to far-red ratio (R:FR) of the incoming light. The low R:FR signal, perceived by phytochromes, initiates a set of responses collectively known as the shade avoidance syndrome, intended to reduce the degree of current or future shade from neighbors by overtopping such competitors or inducing flowering to ensure seed production.

Plant proximity perception dynamically modulates hormone levels and sensitivity in Arabidopsis.

The shade avoidance syndrome (SAS) refers to a set of plant responses initiated after perception by the phytochromes of light enriched in far-red colour reflected from or filtered by neighbouring plants. These varied responses are aimed at anticipating eventual shading from potential competitor vegetation. In Arabidopsis thaliana, the most obvious SAS response at the seedling stage is the increase in hypocotyl elongation.

Cardamine hirsuta: a versatile genetic system for comparative studies.

A major goal in biology is to identify the genetic basis for phenotypic diversity. This goal underpins research in areas as diverse as evolutionary biology, plant breeding and human genetics. A limitation for this research is no longer the availability of sequence information but the development of functional genetic tools to understand the link between changes in sequence and phenotype.

The bHLH proteins BEE and BIM positively modulate the shade avoidance syndrome in Arabidopsis seedlings.

The shade avoidance syndrome (SAS) refers to a set of plant responses initiated after perception by the phytochromes of light with a reduced red to far-red ratio, indicative of vegetation proximity or shade. These responses, including elongation growth, anticipate eventual shading from potential competitor vegetation by overgrowing neighboring plants or flowering to ensure production of viable seeds for the next generation. In Arabidopsis thaliana seedlings, the SAS includes dramatic changes in gene expression, such as induction of PHYTOCHROME RAPIDLY REGULATED 1 (PAR1), encoding an atypical basic helix-loop-helix (bHLH) protein that acts as a transcriptional co-factor to repress hypocotyl elongation.

ATHB4 and HAT3, two class II HD-ZIP transcription factors, control leaf development in Arabidopsis.

In response to plant proximity or canopy shade, plants can react by altering elongation growth and development. Several members of the class II homeodomain-leucine zipper (HD-ZIPII) transcription factor family have been shown to play an instrumental role in the responses to shade. HD-ZIP members of the class III (HD-ZIPIII), by contrast, are involved in basic patterning processes.

A light-regulated genetic module was recruited to carpel development in Arabidopsis following a structural change to SPATULA.

A key innovation of flowering plants is the female reproductive organ, the carpel. Here, we show that a mechanism that regulates carpel margin development in the model flowering plant Arabidopsis thaliana was recruited from light-regulated processes. This recruitment followed the loss from the basic helix-loop-helix transcription factor SPATULA (SPT) of a domain previously responsible for its negative regulation by phytochrome.

Genome-wide binding-site analysis of REVOLUTA reveals a link between leaf patterning and light-mediated growth responses.

Unlike the situation in animals, the final morphology of the plant body is highly modulated by the environment. During Arabidopsis development, intrinsic factors provide the framework for basic patterning processes. CLASS III HOMEODOMAIN LEUCINE ZIPPER (HD-ZIPIII) transcription factors are involved in embryo, shoot and root patterning.