Shade Avoidance Research Articles

PIFs coordinate shade avoidance by inhibiting auxin repressor ARF18 and metabolic regulator QQS.

Shade avoidance syndrome (SAS) arises in densely growing plants that compete for light. In Arabidopsis thaliana, phytochrome interacting factor (PIF) proteins link the perception of shade to stem elongation via auxin production. Here, we report that PIFs inhibit the shade-induced expression of AUXIN RESPONSE FACTOR 18 (ARF18), and ARF18 represses auxin signaling. Therefore, PIF-mediated inhibition of ARF18 enhances auxin-dependent hypocotyl elongation in simulated shade. Furthermore, we show that both PIFs and ARF18 directly repress qua-quine starch (QQS), which controls the allocation of carbon and nitrogen. Shade-repressed QQS attenuates the conversion of starch to protein and thus reduced leaf area. Our results suggest that PIF-dependent gene regulation coordinates multiple SAS responses, including altered stem growth via ARF18, as well as altered leaf growth and metabolism via QQS.

Plant architectural responses in simultaneous maize/soybean strip intercropping do not lead to a yield advantage

AbstractMaize/soybean strip intercropping is a commonly used system throughout China with high crop yields at reduced nutrient input compared to sole maize. Maize is the taller crop, and due to its dominance in light capture over soybean in the intercrop, maize is expected to outperform maize in sole cropping. Conversely, soybean is the subordinate crop and intercropped soybean plants are expected to perform worse than sole soybean. Crop plants show plastic responses in plant architecture to their growing conditions to forage for light and avoid shading. There is little knowledge on plant architectural responses to growing conditions in simultaneous (non‐relay) intercropping and their relationship to species yields. A two‐year field experiment with two simultaneous maize/soybean intercropping systems with narrow and wide strips was conducted to characterise architectural traits of maize and soybean plants grown as intercrop and sole crops. Intercropped maize plants, especially those in border rows, had substantially greater leaf area, biomass and yield than maize plants in sole crops. Intercropped soybean plants, especially those in border rows, had lower leaf area, biomass and yield than sole soybean plants. Overall intercrop performance was similar to that of sole crops, with the land equivalent ratio (LER) being only slightly greater than one (1.03–1.08). Soybean displayed typical shade avoidance responses in the intercrop, such as greater internode elongation and changes in specific leaf area, but these responses could not overcome the consequences of the competition with the taller maize plants. Therefore, in contrast to relay intercrop systems, in the studied simultaneous maize/soybean system, plastic responses did not contribute to practically relevant increases in resource capture and yield at whole system (i.e., intercrop) level.

Genetic Interaction Among Phytochrome, Ethylene and Abscisic Acid Signaling During Dark-Induced Senescence in Arabidopsis thaliana.

Leaf senescence is induced by various internal and external stimuli. Dark-induced senescence has been extensively investigated, but the detailed mechanism underlying it is not well understood. The red light/far-red light receptor phytochrome B and its downstream transcription factors, PYHTOCHROME INTERACTING FACTORs (PIFs) 4 and 5, are known to play an important role in dark-induced senescence. Furthermore, the senescence-inducing phytohormones, ethylene and abscisic acid (ABA) are reported to be involved in dark-induced senescence. In this study, we analyzed the relationship between ethylene, ABA and PIFs in dark-induced leaf senescence. A triple mutant of the core ABA signaling components; SNF1-related protein kinases 2D (SRK2D), SRK2E, and SRK2I, displayed an ABA insensitive phenotype in ABA-induced senescence, whilst the ethylene insensitive mutant ein2 demonstrated low sensitivity to ABA, suggesting that ethylene signaling is involved in ABA-induced senescence. However, the pif4 pif5 mutant did not display low sensitivity to ABA, suggesting that PIF4 and PIF5 act upstream of ABA signaling. Although PIF4 and PIF5 reportedly regulate ethylene production, the triple mutant ein2 pif4 pif5 showed a stronger delayed senescence phenotype than ein2 or pif4 pif5, suggesting that EIN2 and PIF4/PIF5 partially regulate leaf senescence independently of each other. While direct target genes for PIF4 and PIF5, such as LONG HYPOCOTYL IN FAR-RED1 (HFR1) and PHYTOCHROME INTERACTING FACTOR 3-LIKE 1 (PIL1), showed transient upregulation under dark conditions (as is seen in the shade avoidance response), expression of STAY GREEN1 (SGR1), ORESARA1 (ORE1) and other direct target genes of PIF5, continued to increase during dark incubation. It is possible that transcription factors other than PIF4 and PIF5 are involved in the upregulation of SGR1 and ORE1 at a later stage of dark-induced senescence. Possible candidates are senescence-induced senescence regulators (SIRs), which include the NAC transcription factors ORE1 and AtNAP. In fact, ORE1 is known to bind to the SGR1 promoter and promotes its expression. It is therefore inferred that the phytochrome-PIF pathway regulates initial activation of senescence and subsequently, induced SIRs reinforce leaf senescence during dark-induced senescence.

Tongue Refolding in the Knotless Cyanobacterial Phytochrome All2699.

Phytochromes regulate central responses of plants and microorganisms such as shade avoidance and photosystem synthesis. Canonical phytochromes comprise a photosensory module of three domains. The C-terminal phytochrome-specific (PHY) domain interacts via a tongue element with the bilin chromophore in the central GAF (cGMP phosphodiesterase/adenylate cyclase/FhlA) domain. The bilin isomerizes upon illumination with red light, transforming the receptor from the Pr state to the Pfr state. The "knotless" phytochrome All2699 from the cyanobacterium Nostoc sp. PCC7120 comprises three GAF domains as a sensory module and a histidine kinase as an effector. GAF1 and GAF3 both bind a bilin, and GAF2 contains a tongue-like element. We studied the response of All2699, GAF1-GAF2, and GAF1 to red light by Fourier transform infrared difference spectroscopy, including a 13C-labeled protein moiety for assignment. In GAF1-GAF2, a refolding of the tongue from β-sheet to α-helix and an upshift of the ring D carbonyl stretch from 1700 to 1712 cm-1 were observed. Therefore, GAF1-GAF2 is regarded as the smallest model system available to study the tongue response and interaction with the chromophore. Replacement of an arginine in the tongue with proline (R387P) did not affect the unfolding of the β-sheet to Pfr but strongly impaired α-helix formation. In contrast, the Y55H mutation close to bilin ring D did not interfere with conversion to Pfr. Strikingly, the presence of GAF3 in the full-length All2699 diminished the response of the tongue and generated the signal pattern found for GAF1 alone. These results point to a regulatory or integrative role of GAF3 in All2699 that is absent in canonical phytochromes.

UVR8-mediated inhibition of shade avoidance involves HFR1 stabilization in Arabidopsis.

Sun-loving plants perceive the proximity of potential light-competing neighboring plants as a reduction in the red:far-red ratio (R:FR), which elicits a suite of responses called the "shade avoidance syndrome" (SAS). Changes in R:FR are primarily perceived by phytochrome B (phyB), whereas UV-B perceived by UV RESISTANCE LOCUS 8 (UVR8) elicits opposing responses to provide a counterbalance to SAS, including reduced shade-induced hypocotyl and petiole elongation. Here we show at the genome-wide level that UVR8 broadly suppresses shade-induced gene expression. A subset of this gene regulation is dependent on the UVR8-stabilized atypical bHLH transcription regulator LONG HYPOCOTYL IN FAR-RED 1 (HFR1), which functions in part redundantly with PHYTOCHROME INTERACTING FACTOR 3-LIKE 1 (PIL1). In parallel, UVR8 signaling decreases protein levels of the key positive regulators of SAS, namely the bHLH transcription factors PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF5, in a COP1-dependent but HFR1-independent manner. We propose that UV-B antagonizes SAS via two mechanisms: degradation of PIF4 and PIF5, and HFR1- and PIL1-mediated inhibition of PIF4 and PIF5 function. This work highlights the importance of typical and atypical bHLH transcription regulators for the integration of light signals from different photoreceptors and provides further mechanistic insight into the crosstalk of UVR8 signaling and SAS.

MYCs and PIFs Act Independently in Arabidopsis Growth Regulation.

Plants have a variety of strategies to avoid canopy shade and compete with their neighbors for light, collectively called the shade avoidance syndrome (SAS). Plants also have extensive systems to defend themselves against pathogens and herbivores. Defense and shade avoidance are two fundamental components of plant survival and productivity, and there are often tradeoffs between growth and defense. Recently, MYC2, a major positive regulator of defense, was reported to inhibit elongation during shade avoidance. Here, we further investigate the role of MYC2 and the related MYC3 and MYC4 in shade avoidance, and we examine the relationship between MYC2/3/4 and the PIF family of light-regulated transcription factors. We demonstrate that MYC2/3/4 inhibit both elongation and flowering. Furthermore, using both genetic and transcriptomic analysis we find that MYCs and PIFs generally function independently in growth regulation. However, surprisingly, the pif4/5/7 triple mutant restored the petiole shade avoidance response of myc2 (jin1-2) and myc2/3/4. We theorize that increased petiole elongation in myc2/3/4 could be more due to resource tradeoffs or post-translational modifications rather than interactions with PIF4/5/7 affecting gene regulation.

Shade avoidance responses become more aggressive in warm environments.

When exposed to neighbour cues, competitive plants increase stem growth to reduce the degree of current or future shade. The aim of this work is to investigate the impact of weather conditions on the magnitude of shade avoidance responses in Arabidopsis thaliana. We first generated a growth rate database under controlled conditions and elaborated a model that predicts daytime hypocotyl growth as a function of the activity of the main photosensory receptors (phytochromes A and B, cryptochromes 1 and 2) in combination with light and temperature inputs. We then incorporated the action of thermal amplitude to account for its effect on selected genotypes, which correlates with the dynamics of the growth-promoting transcription factor PHYTOCHROME-INTERACTING FACTOR 4. The model predicted growth rate in the field with reasonable accuracy. Thus, we used the model in combination with a worldwide data set of current and future whether conditions. The analysis predicted enhanced shade avoidance responses as a result of higher temperatures due to the geographical location or global warming. Irradiance and thermal amplitude had no effects. These trends were also observed for our local growth rate measurements. We conclude that, if water and nutrients do not become limiting, warm environments enhance the shade avoidance response.

BBX transcriptional factors family in plants-a review

Transcriptional factors play important roles in plant growth, development and responses to stresses. BBX transcriptional factors are characterized with one or two B-box domains in the protein sequence. They are comprehensively involved in photomorphogenesis, flowering, shade avoidance, signal transduction of phytohormones, biotic and abiotic stress responses in plants by regulating gene transcription and interacting with other transcription factors. The classification, structure and functions of BBX of plants are reviewed in this paper.

Phenology matters: Extended spring and autumn canopy cover increases biotic resistance of forests to invasion by common buckthorn (Rhamnus cathartica)

Forest light availability strongly regulates understory community composition, and low availability may confer resistance to invasion by exotic species, yet common buckthorn (Rhamnus cathartica L.) invades North American temperate forests with a broad range of light habitats. It is unclear to what extent buckthorn’s success is due to high mid-season shade tolerance versus shade avoidance permitted by early leaf out and late senescence. We used buckthorn seedlings planted into a forest diversity experiment in Cloquet, Minnesota, USA and a combined buckthorn physiology-canopy light model to test (1) how buckthorn germination, growth, and survival depend on canopy shading and (2) how canopy species richness and phenology affect light availability and buckthorn performance. Based on the mean of May, August, and October light measurements, we found that canopies that permitted ≤3% transmission of incoming light had almost complete mortality of buckthorn and that growth of surviving buckthorn was strongly tied to light availability, but not canopy richness. Compared to deciduous canopies or deciduous-evergreen mixtures, evergreen canopies restricted light availability the most and led to the smallest and least likely to survive buckthorn. Our canopy models further indicated a tight linkage between buckthorn performance and spring and autumn light availability, but not summer light availability. We conclude that spring and autumn light availability are key regulators of buckthorn performance and that buckthorn relies on shade avoidance via an extended phenology to succeed in temperate forests. Consequently, we suggest species with extended spring or autumn canopy cover offer the greatest resistance to invasion, and communities which are often leafless during such periods are most vulnerable to invasion by buckthorn and similar invasive shrubs.

Gibberellins modulate shade-induced soybean hypocotyl elongation downstream of the mutual promotion of auxin and brassinosteroids

Plants and crops are widely suffered by shade stress in the natural communities or in the agricultural fields. The three main phytohormones auxin, gibberellins (GAs) and brassinosteroids (BRs) were found essential in shade avoidance in Arabidopsis. However, their relationship have been seldom reported in plant shade avoidance control. Here, we report our investigation of the crosstalk of auxin, GAs and BRs in shade-induced hypocotyl elongation of soybean. Exogenous feeding of indol-3-acetic acid (IAA), GA3 or 24-epibrassinolide (EBL) distinctly promoted hypocotyl elongation in the white light, while the potent biosynthesis inhibitors of GA3, IAA, BRs severely diminished shade-induced hypocotyl elongation. Synergistic treatment of their biosynthesis inhibitors showed that GA3 fully, while EBL slightly, restored the hypocotyl elongation that was efficiently repressed by IAA biosynthesis inhibitor, GA3 and IAA dramatically suppressed the hypocotyl growth inhibition by BR biosynthesis inhibitor in the shade, whereas both IAA and EBL feeding cannot suppress the elongation inhibition by GA biosynthesis inhibitor. Further analyses revealed that shade remarkably upregulated expression of key genes of IAA, GA and BR biosynthesis in the soybean hypocotyls, and GA biosynthesis genes were effectively blocked by IAA, GA and BR biosynthesis inhibitors in the shade. Taken together, these results suggest that GAs modulate shade-induced hypocotyl elongation downstream of mutual promotion of auxin and BRs in soybean.

A light-dependent molecular link between competition cues and defence responses in plants.

Growth responses to competition1 and defence responses to the attack of consumer organisms2 are two classic examples of adaptive phenotypic plasticity in plants. However, the mechanistic and functional links between these responses are not well understood. Jasmonates, a family of lipid-derived signals, are potent growth inhibitors and central regulators of plant immunity to herbivores and pathogens3,4, with both roles being evolutionarily conserved from bryophytes5 to angiosperms6. When shade-intolerant plants perceive the proximity of competitors using the photoreceptor phytochrome B, they activate the shade-avoidance syndrome and downregulate jasmonate responses7. Despite the central implications of this light-mediated change in the growth/defence balance for plant adaptation and crop yield8,9, the mechanisms by which photoreceptors relay light cues to the jasmonate signalling pathway remain poorly understood10. Here, we identify a sulfotransferase (ST2a) that is strongly upregulated by plant proximity perceived by phytochrome B via the phytochrome B-phytochrome interacting factor signalling module. By catalysing the formation of a sulfated jasmonate derivative, ST2a acts to reduce the pool of precursors of active forms of jasmonates and represents a direct molecular link between photoreceptors and hormone signalling in plants. The metabolic step defined by this enzyme provides a molecular mechanism for prioritizing shade avoidance over defence under intense plant competition.

Sulfation switch in the shade.

Plants adjust the balance between growth and defence using photoreceptors and jasmonates. Levels of active jasmonates are reduced in a phytochrome B-dependent manner by upregulation of a 12-hydroxyjasmonate sulfotransferase, leading to increase in shade avoidance and decrease in defence.

Effects of phytochromes B on growth variability and competitive capacity of maize plants in a canopy

Inter-plant competition is a key trait of maize (Zea mays, L.) crops growth and grain yield. Spatial and temporal availability of resources like water, nutrients and radiation have been proved to impact on this trait. It is suspected that light-quality signals operate on plants´ growth variability of irrigated and fertilized maize crops. Since photoreceptors phytochromes B1 and B2 are involved in light-signals-mediated detecting neighbors, it has been speculated that phytochromes B i) affect plants growth variability from early stages of maize cycle, ii) are involved in the increasing inter-plant variability by increasing plant density, and iii) confer a higher competitive capacity of plants within a canopy. It is also unclear if shade avoidance responses are detrimental or beneficial for plants growth and grain yield in maize crops. To test these hypothesis, plants of maize inbred line France 2 wild type (WT) and the isogenic mutants lacking either phyB1 or phyB2 (phyB1 and phyB2), were cultivated in the field during two seasons in monocultures (WT, phyB1, phyB2; hypothesis i and ii) and polycultures (WT/phyB1, WT/phyB2, phyB1/phyB2 and WT/phyB1/phyB2; hypothesis iii) at contrasting plant densities (low and high) irrigated and fertilized. Plant biomass of ten tagged plants per plot were nondestructively estimated from seedling emergence to 15 days after flowering, and from individual samples at physiological maturity and coefficient of variation (CV) of plant biomass was calculated as a proxy of plants growth variability. Plant leaf area, stem length, and plant growth rate of tagged plans were measured around female flowering, i.e. silking (PGRs) and kernel number per plant (KNP) and grain yield were quantified at physiological maturity. At the lower density, no differences in plants growth variability were detected among genotypes. By contrast, at the higher density CV of WT was higher than those of mutant lines only when canopies were fully developed (i.e. after flowering). Taller plants with larger leaf area characterized WT phenotype at all densities and polycultures, which were generally reflected on higher PGRs. These reactions of WT plants allowed them to acquire more competitive ability and to set more KNP and grain yield than phyB1 plants. phyB2 may have offset differences in KNP with WT by greater grain weights. Hence, in maize crops, phytochromes B are key photoreceptors mediating the response of plants growth variability to crowding stress, without any detrimental effect on grain yield because the ability of plants to forage for light, sustains PGRs and kernel setting.

Do plants adaptively respond to future competition?

Plants can detect the presence of competitors through the change the spectral quality of light induced by potentially competing plants. This change in spectral quality can induce shade avoidance plasticity to maximise light acquisition. We examined how simulated competition as seedlings impact performance when plants are exposed to real competition later in life. We predicted that individuals experiencing simulated competition as seedlings will perform better under competition later in life. We grew seedlings of six short-lived herbaceous species under simulated competition and no competition treatments early in life and real competition and no competition later in life. Seedlings in the real competition treatment were grown in pots with grass competitors. Competitors were prevented from interacting with seedlings early in the experiment using above ground by pinning back competitor plants, and below ground through root exclusion pots. We ended the simulated competition treatment and started the real competition treatment (by removing the barriers) when seedlings reached a threshold size. We found that plants in the simulated competition treatment did not express shade-avoidance plasticity. No species performed better under competition when exposed to simulated competition as seedlings. Three of the six species performed significantly worse under competition when exposed to simulated competition as seedlings. Plants are often capable of detecting and responding to their enemies. However, none of the species in our study demonstrated either the capacity to detect the presence of competitors, or increased performance under competition when exposed to the cues for future competition early in life. In some instances, plants respond passively to competitors and adaptive responses to the presence of enemies can be limited.

Central clock components modulate plant shade avoidance by directly repressing transcriptional activation activity of PIF proteins

Light-environment signals, sensed by plant phytochrome photoreceptors, are transduced to target genes through direct regulation of PHYTOCHROME-INTERACTING FACTOR (PIF) transcription factor abundance and activity. Previous genome-wide DNA-binding and expression analysis has identified a set of genes that are direct targets of PIF transcriptional regulation. However, quantitative analysis of promoter occupancy versus expression level has suggested that unknown "trans factors" modulate the intrinsic transcriptional activation activity of DNA-bound PIF proteins. Here, using computational analysis of published data, we have identified PSEUDO-RESPONSE REGULATORS (PRR5 and PRR7) as displaying a high frequency of colocalization with the PIF proteins at their binding sites in the promoters of PIF Direct Target Genes (DTGs). We show that the PRRs function to suppress PIF-stimulated growth in the light and vegetative shade and that they repress the rapid PIF-induced expression of PIF-DTGs triggered by exposure to shade. The repressive action of the PRRs on both growth and DTG expression requires the PIFs, indicating direct action on PIF activity, rather than a parallel antagonistic pathway. Protein interaction assays indicate that the PRRs exert their repressive activity by binding directly to the PIF proteins in the nucleus. These findings support the conclusion that the PRRs function as direct outputs from the core circadian oscillator to regulate the expression of PIF-DTGs through modulation of PIF transcriptional activation activity, thus expanding the roles of the multifunctional PIF-signaling hub.

Shade avoidance and reproductive strategies of an early successional species Penthorum chinense in relation to shade treatments.

Shade avoidance is expected to be favoured under moderate light. However, in previous studies, shade avoidance was highest in the deepest shade, despite the fact that the plants incur the costs of shade avoidance without the benefits of being exposed to increased light. We performed shading experiments under different light intensities to understand: (i) how shade avoidance traits of Penthorum chinense could peak in moderate light, and (ii) if there was a trade-off between plant height and allocation of seeds along the light gradients. Penthorum chinense increased shade avoidance traits such as height per total dry mass as the amount of light decreased. Side stem number per total dry mass of P. chinense decreased as shade became deeper, from full light to low light. Regressions on seed mass fraction and height were significant with a linear model (y=-0.0006x+0.1338). There were more resources allocated to seeds under low light than under moderate light. Penthorum chinense increased shade avoidance traits with the decrease in light amount, as found in previously studied species. There was a trade-off between height and production of more seeds. The reproductive strategy of P. chinense was to increase seed mass fraction under low light more than under moderate light. This species might be able to expand established populations by both rhizomes and seeds under low light environments.

ZEITLUPE is required for shade avoidance in the wild tobaccoNicotiana attenuata

Being shaded is a common environmental stress for plants, especially for densely planted crops. Shade decreases red: far-red (R:FR) ratios that inactivate phytochrome B (PHYB) and subsequently release p̱hytochrome i̱nteraction f̱actors (PIFs). Shaded plants display elongated hypocotyls, internodes, and petioles, hyponastic leaves, early flowering and are inhibited in branching: traits collectively called the shade avoidance syndrome (SAS). ZEITLUPE (ZTL) is a circadian clock component and blue light photoreceptor, which is also involved in floral rhythms and plant defense in Nicotiana attenuata. ztl mutants are hypersensitive to red light and ZTL physically interacts with PHYB, suggesting the involvement of ZTL in R:FR light signaling. Here, we show that N. attenuata ZTL-silenced plants display a phenotype opposite to that of the SAS under normal light. After simulated shade, the normally induced transcript levels of the SAS marker gene, ATHB2 are attenuated in ZTL-silenced plants. The auxin signaling pathway, known to be involved in SAS, was also significantly attenuated. Furthermore, NaZTL directly interacts with NaPHYBs, and regulates the transcript levels of PHYBs, PIF3a, PIF7 and PIF8 under shade. Our results suggest that ZTL may regulate PHYB- and the auxin-mediated signaling pathway, which functions in the SAS of N. attenuata.

Shade‐induced plasticity in invasive Impatiens glandulifera populations

SummaryPhenotypic plasticity, which confers a fitness advantage under heterogeneous and novel environments, has been commonly suggested to contribute to the success of invasive plants in their introduced range. For example, plasticity in response to changes in light availability could facilitate invasiveness by allowing plants to both rapidly establish in unshaded, disturbed habitats, and tolerate shaded or crowded environments. The plastic responses of invasive plants to shade were mostly studied in morphological traits. However, plasticity in physiological traits might provide more rapid and reversible responses and thus be more effective in environments with rapid temporal variations. Here, we compared plasticity in a range of morphological and physiological traits that provide shade avoidance or tolerance between two native and six introduced populations of Impatiens glandulifera. In a common garden, we subjected second‐generation siblings of native and invasive plants to two light availability treatments and measured their morphological, physiological and performance responses. Impatiens glandulifera from invasive populations exhibited greater phenotypic plasticity in response to light availability in four out of 12 measured traits. Moreover, this greater plasticity was mostly limited to physiological traits associated with photosynthetic acclimation. These results suggest high phenotypic plasticity in response to light availability could have facilitated I. glandulifera's spread in both disturbed habitats and woodlands or under intense light competition. The results of this study highlight the importance of considering physiological traits when studying the role of plasticity in the success of invasive plants.

HISTONE DEACETYLASE 9 stimulates auxin-dependent thermomorphogenesis in Arabidopsis thaliana by mediating H2A.Z depletion

Many plant species respond to unfavorable high ambient temperatures by adjusting their vegetative body plan to facilitate cooling. This process is known as thermomorphogenesis and is induced by the phytohormone auxin. Here, we demonstrate that the chromatin-modifying enzyme HISTONE DEACETYLASE 9 (HDA9) mediates thermomorphogenesis but does not interfere with hypocotyl elongation during shade avoidance. HDA9 is stabilized in response to high temperature and mediates histone deacetylation at the YUCCA8 locus, a rate-limiting enzyme in auxin biosynthesis, at warm temperatures. We show that HDA9 permits net eviction of the H2A.Z histone variant from nucleosomes associated with YUCCA8, allowing binding and transcriptional activation by PHYTOCHROME INTERACTING FACTOR 4, followed by auxin accumulation and thermomorphogenesis.

Canopy Light Quality Modulates Stress Responses in Plants.

Plants growing at high density are in constant competition for light with each other. The shade avoidance syndrome (SAS) is an effective way to escape neighboring vegetation. Even though the molecular mechanisms regulating SAS have been long studied, interactions between light and other environmental signaling pathways have only recently received attention. Under natural conditions, plants deal with multiple stresses simultaneously. It is, therefore, key to identify commonalities, distinctions, and interactions between plant responses to different environmental cues. This review outlines the current understanding of the interplay between canopy light signaling and other stresses, both biotic and abiotic. Understanding plant responses to multiple stimuli, factoring in the dominance of light for plant life, is essential to generate crops with increased resilience against climate change.