PHYTOCHROME INTERACTING FACTOR Research Articles

Maize WRKY28 interacts with the DELLA protein D8 to affect skotomorphogenesis and participates in the regulation of shade avoidance and plant architecture.

Competition for light from neighboring vegetation can trigger the shade-avoidance response (SAR) in plants, which is detrimental to their yield. The molecular mechanisms regulating SAR are well established in Arabidopsis, and some regulators of skotomorphogenesis have been found to be involved in the regulation of the SAR and plant architecture. However, the role of WRKY transcription factors in this process has rarely been reported, especially in maize (Zea mays). Here, we report that maize Zmwrky28 mutants exhibit shorter mesocotyls in etiolated seedlings. Molecular and biochemical analyses demonstrate that ZmWRKY28 directly binds to the promoter regions of the Small Auxin Up RNA (SAUR) gene ZmSAUR54 and the Phytochrome-Interacting Factor (PIF) gene ZmPIF4.1 to activate their expression. In addition, the maize DELLA protein Dwarf Plant8 (D8) interacts with ZmWRKY28 in the nucleus to inhibit its transcriptional activation activity. We also show that ZmWRKY28 participates in the regulation of the SAR, plant height, and leaf rolling and erectness in maize. Taken together, our results reveal that ZmWRKY28 is involved in GA-mediated skotomorphogenic development and can be used as a potential target to regulate SAR for breeding of high-density-tolerant cultivars.

PHYTOCHROME-INTERACTING FACTORS are involved in starch degradation adjustment via inhibition of the carbon metabolic regulator QUA-QUINE STARCH in Arabidopsis.

As sessile organisms, plants encounter dynamic and challenging environments daily, including abiotic/biotic stresses. The regulation of carbon and nitrogen allocations for the synthesis of plant proteins, carbohydrates, and lipids is fundamental for plant growth and adaption to its surroundings. Light, one of the essential environmental signals, exerts a substantial impact on plant metabolism and resource partitioning (i.e., starch). However, it is not fully understood how light signaling affects carbohydrate production and allocation in plant growth and development. An orphan gene unique to Arabidopsis thaliana, named QUA-QUINE STARCH (QQS) is involved in the metabolic processes for partitioning of carbon and nitrogen among proteins and carbohydrates, thus influencing leaf, seed composition, and plant defense in Arabidopsis. In this study, we show that PHYTOCHROME-INTERACTING bHLH TRANSCRIPTION FACTORS (PIFs), including PIF4, are required to suppress QQS during the period at dawn, thus preventing overconsumption of starch reserves. QQS expression is significantly de-repressed in pif4 and pifQ, while repressed by overexpression of PIF4, suggesting that PIF4 and its close homologs (PIF1, PIF3, and PIF5) act as negative regulators of QQS expression. In addition, we show that the evening complex, including ELF3 is required for active expression of QQS, thus playing a positive role in starch catabolism during night-time. Furthermore, QQS is epigenetically suppressed by DNA methylation machinery, whereas histone H3 K4 methyltransferases (e.g., ATX1, ATX2, and ATXR7) and H3 acetyltransferases (e.g., HAC1 and HAC5) are involved in the expression of QQS. This study demonstrates that PIF light signaling factors help plants utilize optimal amounts of starch during the night and prevent overconsumption of starch before its biosynthesis during the upcoming day.

HSP90s are required for hypocotyl elongation during skotomorphogenesis and thermomorphogenesis via the COP1-ELF3-PIF4 pathway in Arabidopsis.

Light and temperature are two key environmental signals that share several molecular components that, in turn, regulate plant growth. Darkness and high ambient temperatures promote skoto- and thermomorphogenesis, including stem elongation. Heat shock proteins 90 (HSP90s) facilitate the adaptation of organisms to various adverse environmental stimuli. Here, we showed that HSP90s are required for hypocotyl elongation during both skoto- and thermomorphogenesis. When HSP90s activities are impaired by the knockdown of HSP90s expression or the application of HSP90 inhibitors, the expression levels and protein abundance of PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) markedly decreased. EARLY FLOWERING 3 (ELF3) deficiency was resistant to the inhibition of HSP90s activities. Furthermore, HSP90s interacted with and destabilized ELF3. In the CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) mutant, the changes in endogenous PIF4 and ELF3 protein levels caused by the inhibition of HSP90s activities were abolished. HSP90s enhanced the interaction between COP1 and ELF3, reduced ELF3 functional effects on PIF4 and modulated hypocotyl elongation during skoto- and thermomorphogenesis. Our results indicated that HSP90s participate in light and temperature signalling via the COP1-ELF3-PIF4 module to regulate hypocotyl growth in changing environments.

Optical Control of Cell Signaling with Red/Far-Red Light-Responsive Optogenetic Tools in Caenorhabditis elegans.

Optogenetic techniques have been intensively applied to the nematode Caenorhabditis elegans to investigate its neural functions. However, as most of these optogenetics are responsive to blue light and the animal exhibits avoidance behavior to blue light, the application of optogenetic tools responsive to longer wavelength light has been eagerly anticipated. In this study, we report the implementation in C.elegans of a phytochrome-based optogenetic tool that responds to red/near-infrared light and manipulates cell signaling. We first introduced the SynPCB system, which enabled us to synthesize phycocyanobilin (PCB), a chromophore for phytochrome, and confirmed the biosynthesis of PCB in neurons, muscles, and intestinal cells. We further confirmed that the amount of PCBs synthesized by the SynPCB system was sufficient for photoswitching of phytochrome B (PhyB)-phytochrome interacting factor 3 (PIF3). In addition, optogenetic elevation of intracellular Ca2+ levels in intestinal cells induced a defecation motor program. These SynPCB system and phytochrome-based optogenetic techniques would be of great value in elucidating the molecular mechanisms underlying C.elegans behaviors.

PIF8-WRKY42-mediated salicylic acid synthesis modulates red light induced powdery mildew resistance in oriental melon.

Light signals and plant hormones are involved in regulating the growth, development and stress resistance of plants; however, it remains unclear whether light affects hormones and thus pathogen resistance in oriental melon. Here, we found that red light promoted salicylic acid (SA) accumulation and powdery mildew resistance by activating the transcription of CmICS, the key gene for SA biosynthesis, and silencing CmICS seriously weakened the induction effect of red light on powdery mildew resistance in oriental melon leaves. Further studies showed that red light induced the expression of CmWRKY42 under powdery mildew stress, and CmWRKY42 directly bound to the CmICS promoter to activate its expression and promote the accumulation of SA under red light. Furthermore, we found that PHYTOCHROME INTERACTING FACTOR 8 (PIF8), as a negative regulator of SA biosynthesis, inhibits CmWRKY42 transcriptional activation by binding to the CmWRKY42 promoter, and thus inhibits transcriptional activation of CmICS by CmWRKY42. Also, CmPIF8 binds to the CmICS promoter and directly inhibits its transcription. In conclusion, our study revealed a new molecular mechanism of the relationship between red light-SA-powdery mildew resistance and provided a theoretical basis for resistance breeding of oriental melon.

Genome-Wide Characterization of the PIFs Family in Sweet Potato and Functional Identification of IbPIF3.1 under Drought and Fusarium Wilt Stresses.

Phytochrome-interacting factors (PIFs) are essential for plant growth, development, and defense responses. However, research on the PIFs in sweet potato has been insufficient to date. In this study, we identified PIF genes in the cultivated hexaploid sweet potato (Ipomoea batatas) and its two wild relatives, Ipomoea triloba, and Ipomoea trifida. Phylogenetic analysis revealed that IbPIFs could be divided into four groups, showing the closest relationship with tomato and potato. Subsequently, the PIFs protein properties, chromosome location, gene structure, and protein interaction network were systematically analyzed. RNA-Seq and qRT-PCR analyses showed that IbPIFs were mainly expressed in stem, as well as had different gene expression patterns in response to various stresses. Among them, the expression of IbPIF3.1 was strongly induced by salt, drought, H2O2, cold, heat, Fusarium oxysporum f. sp. batatas (Fob), and stem nematodes, indicating that IbPIF3.1 might play an important role in response to abiotic and biotic stresses in sweet potato. Further research revealed that overexpression of IbPIF3.1 significantly enhanced drought and Fusarium wilt tolerance in transgenic tobacco plants. This study provides new insights for understanding PIF-mediated stress responses and lays a foundation for future investigation of sweet potato PIFs.

PHYTOCHROME INTERACTING FACTOR 4 regulates microtubule organization to mediate high temperature-induced hypocotyl elongation in Arabidopsis.

Hypocotyl elongation is an important morphological response during plant thermomorphogenesis. Multiple studies indicate that the transcription factor PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) is a key regulator of high temperature-induced hypocotyl elongation. However, the underlying cellular mechanisms regarding PIF4-mediated hypocotyl elongation are largely unclear. In this study, we found that PIF4 regulates the PLANT U-BOX TYPE E3 UBIQUITIN LIGASE 31 (PUB31)-SPIRAL1 (SPR1) module and alters cortical microtubule reorganization to promote hypocotyl cell elongation during Arabidopsis thaliana (Arabidopsis) thermomorphogenesis. SPR1 loss-of-function mutants exhibit much shorter hypocotyls when grown at 28 °C, indicating a positive role for SPR1 in high ambient temperature-induced hypocotyl elongation. High ambient temperature induces SPR1 expression in a PIF4-dependent manner, and stabilizes SPR1 protein to mediate microtubule reorganization. Further investigation showed that PUB31 interacts with and ubiquitinates SPR1. In particular, the ubiquitinated effect on SPR1 was moderately decreased at high temperature, which was due to the direct binding of PIF4 to the PUB31 promoter and down-regulating its expression. Thus, this study reveals a mechanism in which PIF4 induces SPR1 expression and suppresses PUB31 expression, resulting in the accumulation and stabilization of SPR1 protein, and further promoting hypocotyl cell elongation by altering cortical microtubule organization during Arabidopsis thermomorphogenesis.

FAR-RED ELONGATED HYPOCOTYL3 increases leaf longevity by delaying senescence in arabidopsis.

Senescence is the final stage of leaf development, limits and dictates the longevity of leaf. This stage is strictly controlled by internal developmental age signals and external environmental signals. However, the underlying mechanisms by which various signals integrating together to regulate leaf senescence remain largely unknown. Here, we show that the light signalling protein FAR-RED ELONGATED HYPOCOTYL3 (FHY3) directly represses the transcription of PHYTOCHROME-INTERACTING FACTOR4 (PIF4) and NON-YELLOWING1/STAY-GREEN1 (NYE1/SGR1), two key regulators of senescence, thus preventing chlorophyll degradation and extending the leaf longevity in Arabidopsis thaliana. Disrupting either PIF4 or NYE1 function completely rescued the early leaf senescence of fhy3-4 mutant. Interestingly, we found that FHY3 competes with PIF4 to bind to the G-box cis-element in NYE1 promoter, subsequently preventing the transcriptional activation of this gene by PIF4. Moreover, FHY3 transcript levels gradually increased in senescent leaves, which consist with disrupting FHY3 function accelerated chlorophyll degradation and shorted the leaf longevity. All these findings reveal that FHY3 is a master regulator that participates in multiple signalling pathways to increase leaf longevity. In addition, our study shed light on the dynamic regulatory mechanisms by which plants integrate light signalling and internal developmental cues to control leaf senescence and longevity.

Integrative analysis of transcriptome and metabolome revealed the mechanisms by which flavonoids and phytohormones regulated the adaptation of alfalfa roots to NaCl stress.

Salinity critically affects the growth and development of alfalfa (Medicago sativa), making it necessary to understand the molecular mechanism of alfalfa's adaptation to salt stress. In this study, alfalfa roots were subjected to salt stress and transcriptomics and metabolomics analyses were performed. The results showed that flavonoid synthesis, hormone synthesis, and transduction pathways may be involved in the alfalfa salt stress adaptation reaction, and that they are related. Combined analysis of differential genes and differential metabolites found that dihydroquercetin and beta-ring hydroxylase (LUT5), ABA responsive element binding factor 2 (ABF2), protein phosphatase PP2C (PP2C) and abscisic acid (ABA) receptor PYL2 (PYL), luteolinidin was significantly correlated with PP2C and phytochrome-interacting factor 4 (PIF4) and (+)-7-isomethyl jasmonate were significantly correlated with flavonol synthase (FLS) gene. (+)-7-isomethyl jasmonate and homoeriodictyol chalcone were significantly correlated with peroxidase (POD). POD was significantly up-regulated under NaCl stress for 6 and 24 h. Moreover, flavonoids, gibberellin (GA), jasmonic acid (JA) and ABA were suggested to play an important role in alfalfa's response to salt stress. Further, GA,ABA, and JA may be involved in the regulation of flavonoids to improve alfalfa's salt tolerance, and JA may be a key signal to promote the synthesis of flavonoids. This study revealed the possible molecular mechanism of alfalfa adaptation to salt stress, and identified a number of salt-tolerance candidate genes from the synthesis and signal transduction pathways of flavonoids and plant hormones, providing new insights into the regulatory network of alfalfa response to salt stress.

Cryptochromes suppress leaf senescence in response to blue light in Arabidopsis.

The induction and progression of leaf senescence are effectively changed according to the light environment. The leaf senescence response is enhanced when plants are grown under a dense shade cast by neighboring vegetation. Although the fluence rate of the red and blue regions in the light spectrum is strongly attenuated under shade, photosensory mechanisms that underpin the blue light response are still unclear. In this study, we analyzed leaf senescence in response to blue light in Arabidopsis (Arabidopsis thaliana). We found that leaf senescence was promoted by the elimination of active phytochrome Pfr by pulsed far-red (FR) light, whereas irradiation with blue light suppressed leaf senescence in the wild type but not in the cryptochrome (CRY)-deficient mutant, cry1 cry2. Hence, two light-sensing modes contributed to the suppression of leaf senescence that was dependent on light spectrum features. First was the leaf senescence response to blue light, which was mediated exclusively by cryptochromes. Second was the phytochrome-mediated leaf senescence response to red/FR light. Physiological analysis of transgenic plants expressing green fluorescent protein (GFP)-tagged CRY2 revealed that photo-activation of cryptochromes was required to suppress leaf senescence in response to blue light. Transcriptomic analysis further uncovered the molecular and cellular processes involved in the regulation of leaf senescence downstream of cryptochromes. Furthermore, analysis of cryptochrome-downstream components indicated that ELONGATED HYPOCOTYL 5 (HY5) and PHYTOCHROME INTERACTING FACTOR (PIF) 4 and PIF5 were required for suppression and promotion of leaf senescence, respectively.

ZTL regulates thermomorphogenesis through TOC1 and PRR5.

Plants adapt to high temperature stresses through thermomorphogenesis, a process that includes stem elongation and hyponastic leaf growth. Thermomorphogenesis is gated by the circadian clock through two evening-expressed clock components, TIMING OF CAB EXPRESSION1(TOC1) and PSEUDO-RESPONSE REGULATORS5(PRR5). These proteins directly interact with and inhibit PHYTOCHROME INTERACTING FACTOR4(PIF4), a basic helix-loop-helix transcription factor that promotes thermoresponsive growth. PIF4-mediated thermoresponsive growth is positively regulated by ZEITLUPE(ZTL), a central clock component, but the molecular mechanisms underlying this are poorly understood. Here, we show that ZTL regulates thermoresponsive growth through TOC1 and PRR5. Genetic analyses reveal that ZTL regulates PIF4 activity as well as PIF4 expression. In Arabidopsis thaliana, ztl mutants exhibit highly accumulated TOC1 and PRR5 and unresponsive expression of PIF4 target genes under exposure to high temperatures. Mutations in TOC1 and PRR5 restore thermoactivation of PIF4 target genes and thermoresponsive growth in ztl mutants. We also show that the molecular chaperone heat-shock protein90 promotes thermoresponsive growth through the ZTL-TOC1/PRR5 signaling module. Further, we show that ZTL protein stability is increased at high temperatures. Taken together, our results demonstrate that ZTL-mediated degradation of TOC1 and PRR5 enhances the sensitivity of hypocotyl growth to high temperatures.

Author Correction: PHYTOCHROME-INTERACTING FACTORs trigger environmentally responsive chromatin dynamics in plants

Author Correction: PHYTOCHROME-INTERACTING FACTORs trigger environmentally responsive chromatin dynamics in plants

Regulation of Plant Photoresponses by Protein Kinase Activity of Phytochrome A.

Extensive research has been conducted for decades to elucidate the molecular and regulatory mechanisms for phytochrome-mediated light signaling in plants. As a result, tens of downstream signaling components that physically interact with phytochromes are identified, among which negative transcription factors for photomorphogenesis, PHYTOCHROME-INTERACTING FACTORs (PIFs), are well known to be regulated by phytochromes. In addition, phytochromes are also shown to inactivate an important E3 ligase complex consisting of CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) and SUPPRESSORs OF phyA-105 (SPAs). This inactivation induces the accumulation of positive transcription factors for plant photomorphogenesis, such as ELONGATED HYPOCOTYL 5 (HY5). Although many downstream components of phytochrome signaling have been studied thus far, it is not fully elucidated which intrinsic activity of phytochromes is necessary for the regulation of these components. It should be noted that phytochromes are autophosphorylating protein kinases. Recently, the protein kinase activity of phytochrome A (phyA) has shown to be important for its function in plant light signaling using Avena sativa phyA mutants with reduced or increased kinase activity. In this review, we highlight the function of phyA as a protein kinase to explain the regulation of plant photoresponses by phyA.

Effect of the biosynthesis of the volatile compound phenylacetaldehyde on chloroplast modifications in tea (Camellia sinensis) plants.

Plant volatile compounds have important physiological and ecological functions. Phenylacetaldehyde (PAld), a volatile phenylpropanoid/benzenoid, accumulates in the leaves of tea (Camellia sinensis) plants grown under continuous shading. This study was conducted to determine whether PAld production is correlated with light and to elucidate the physiological functions of PAld in tea plants. Specifically, the upstream mechanism modulating PAld biosynthesis in tea plants under different light conditions as well as the effects of PAld on chloroplast/chlorophyll were investigated. The biosynthesis of PAld was inhibited under light, whereas it was induced in darkness. The structural gene encoding aromatic amino acid aminotransferase 1 (CsAAAT1) was expressed at a high level in darkness, consistent with its importance for PAld accumulation. Additionally, the results of a transcriptional activation assay and an electrophoretic mobility shift assay indicated CsAAAT1 expression was slightly activated by phytochrome-interacting factor 3-2 (CsPIF3-2), which is a light-responsive transcription factor. Furthermore, PAld might promote the excitation of chlorophyll in dark-treated chloroplasts and mediate electron energy transfer in cells. However, the accumulated PAld can degrade chloroplasts and chlorophyll, with potentially detrimental effects on photosynthesis. Moreover, PAld biosynthesis is inhibited in tea leaves by red and blue light, thereby decreasing the adverse effects of PAld on chloroplasts during daytime. In conclusion, the regulated biosynthesis of PAld in tea plants under light and in darkness leads to chloroplast modifications. The results of this study have expanded our understanding of the biosynthesis and functions of volatile phenylpropanoids/benzenoids in tea leaves.

Shade avoidance in the context of climate change.

When exposed to changes in the light environment caused by neighboring vegetation, shade-avoiding plants modify their growth and/or developmental patterns to access more sunlight. In Arabidopsis (Arabidopsis thaliana), neighbor cues reduce the activity of the photosensory receptors phytochrome B (phyB) and cryptochrome 1, releasing photoreceptor repression imposed on PHYTOCHROME INTERACTING FACTORs (PIFs) and leading to transcriptional reprogramming. The phyB-PIF hub is at the core of all shade-avoidance responses, whilst other photosensory receptors and transcription factors contribute in a context-specific manner. CONSTITUTIVELY PHOTOMORPHOGENIC1 is a master regulator of this hub, indirectly stabilizing PIFs and targeting negative regulators of shade avoidance for degradation. Warm temperatures reduce the activity of phyB, which operates as a temperature sensor and further increases the activities of PIF4 and PIF7 by independent temperature sensing mechanisms. The signaling network controlling shade avoidance is not buffered against climate change; rather, it integrates information about shade, temperature, salinity, drought, and likely flooding. We, therefore, predict that climate change will exacerbate shade-induced growth responses in some regions of the planet while limiting the growth potential in others.

Guard cell activity of PIF4 and HY5 control transpiration

Whole-plant transpiration, controlled by plant hydraulics and stomatal movement, is regulated by endogenous and environmental signals, with the light playing a dominant role. Stomatal pore size continuously adjusts to changes in light intensity and quality to ensure optimal CO2 intake for photosynthesis on the one hand, together with minimal water loss on the other. The link between light and transpiration is well established, but the genetic knowledge of how guard cells perceive those signals to affect stomatal conductance is still somewhat limited. In the current study, we evaluated the role of two central light-responsive transcription factors; a bZIP-family transcription factor ELONGATED HYPOCOTYL5 (HY5) and the basic helix-loop-helix (BHLH) transcription factor PHYTOCHROME INTERACTING FACTOR4 (PIF4), in the regulation of steady-state transpiration. We show that overexpression of PIF4 exclusively in guard cells (GCPIF4) decreases transpiration, and can restrain the high transpiration of the pif4 mutant. Expression of HY5 specifically in guard cells (GCHY5) had the opposite effect of enhancing transpiration rates of WT- Arabidopsis and tobacco plants and of the hy5 mutant in Arabidopsis. In addition, we show that GCHY5 can reverse the low transpiration caused by guard cell overexpression of the sugar sensor HEXOKINASE1 (HXK1, GCHXK), an established low transpiring genotype. Finally, we suggest that the GCHY5 reversion of low transpiration by GCHXK requires the auto-activation of the endogenous HY5 in other tissues. These findings support the existence of an ongoing diurnal regulation of transpiration by the light-responsive transcription factors HY5 and PIF4 in the stomata, which ultimately determine the whole-plant water use efficiency.

The Mediator complex subunit MED25 interacts with HDA9 and PIF4 to regulate thermomorphogenesis.

Thermomorphogenesis is, among other traits, characterized by enhanced hypocotyl elongation due to the induction of auxin biosynthesis genes like YUCCA8 by transcription factors, most notably PHYTOCHROME INTERACTING FACTOR 4 (PIF4). Efficient binding of PIF4 to the YUCCA8 locus under warmth depends on HISTONE DEACETYLASE 9 (HDA9) activity, which mediates histone H2A.Z depletion at the YUCCA8 locus. However, HDA9 lacks intrinsic DNA-binding capacity, and how HDA9 is recruited to YUCCA8, and possibly other PIF4-target sites, is currently not well understood. The Mediator complex functions as a bridge between transcription factors bound to specific promoter sequences and the basal transcription machinery containing RNA polymerase II. Mutants of Mediator component Mediator25 (MED25) exhibit reduced hypocotyl elongation and reduced expression of YUCCA8 at 27°C. In line with a proposed role for MED25 in thermomorphogenesis in Arabidopsis (Arabidopsis thaliana), we demonstrated an enhanced association of MED25 to the YUCCA8 locus under warmth and interaction of MED25 with both PIF4 and HDA9. Genetic analysis confirmed that MED25 and HDA9 operate in the same pathway. Intriguingly, we also showed that MED25 destabilizes HDA9 protein. Based on our findings, we propose that MED25 recruits HDA9 to the YUCCA8 locus by binding to both PIF4 and HDA9.

Independent Responses of Photosynthesis and Plant Morphology to Alterations of PIF Proteins and Light-Dependent MicroRNA Contents in Arabidopsis thaliana pif Mutants Grown under Lights of Different Spectral Compositions

The effects of the quality of light on the content of phytochrome interacting factors (PIFs) such as PIF3, PIF4 and PIF5, as well as the expression of various light-dependent microRNAs, in adult Arabidopsis thaliana pif mutant plants (pif4, pif5, pif3pif5, pif4pif5, pif3pif4pif5) were studied. We demonstrate that under blue light, the pif4 mutant had maximal expression of most of the studied microRNAs (miR163, miR319, miR398, miR408, miR833) when the PIF4 protein in plants was reduced. This finding indicates that the PIF4 protein is involved in the downregulation of this group of microRNAs. This assumption is additionally confirmed by the fact that under the RL spectrum in pif5 mutants, practically the same miRNAs decrease expression against the background of an increase in the amount of PIF4 protein. Unlike the WT and other mutants, the pif4 mutant responded to the BL spectrum not only by activating the expression of light-dependent miRNAs, but also by a significant increase in the expression of transcription factors and key light signalling genes. These molecular reactions do not affect the activity of photosynthesis but may be involved in the formation of a light quality-dependent phenotype.

Regulatory Mechanisms of Heat Stress Response and Thermomorphogenesis in Plants.

As worldwide warming intensifies, the average temperature of the earth continues to increase. Temperature is a key factor for the growth and development of all organisms and governs the distribution and seasonal behavior of plants. High temperatures lead to various biochemical, physiological, and morphological changes in plants and threaten plant productivity. As sessile organisms, plants are subjected to various hostile environmental factors and forced to change their cellular state and morphological architecture to successfully deal with the damage they suffer. Therefore, plants have evolved multiple strategies to cope with an abnormal rise in temperature. There are two main mechanisms by which plants respond to elevated environmental temperatures. One is the heat stress response, which is activated under extremely high temperatures; the other is the thermomorphogenesis response, which is activated under moderately elevated temperatures, below the heat-stress range. In this review, we summarize recent progress in the study of these two important heat-responsive molecular regulatory pathways mediated, respectively, by the Heat Shock Transcription Factor (HSF)-Heat Shock Protein (HSP) pathway and PHYTOCHROME INTER-ACTING FACTOR 4 (PIF4) pathways in plants and elucidate the regulatory mechanisms of the genes involved in these pathways to provide comprehensive data for researchers studying the heat response. We also discuss future perspectives in this field.

Comprehensive Analysis of Betula platyphylla Suk. PIF Gene Family and Their Potential Functions in Growth and Development

Phytochrome-interacting factors (PIFs) are transcription factors with the basic helix-loop-helix (bHLH) domain. As integration factors between different signal pathways, members of the PIF protein family regulate many aspects of plant growth and development, such as seed germination, photomorphogenesis, thermomorphogenesis, rhythm regulation, flowering response, stomatal development, and stress responses. Our previous studies have shown that the BpSPL2 gene may regulate plants' adventitious root development through PIF genes. Within the Betula platyphylla genome, we identified eight PIF (BpPIFs) genes. We analysed and named them based on a phylogenetic tree, gene structures, and conserved motifs. Synteny analysis indicated that transposition or segmental duplication events played a minor role in the expansion of BpPIFs. The comparative syntenic analysis combined with phylogenetic analysis provided a deep insight into the phylogenetic relationships of BpPIF genes, suggesting that BpPIF proteins are closer to PtPIF than to AtPIF. The analysis of cis-acting elements in promoter regions of BpPIF genes indicated that various elements were related to light, abiotic stress, and plant hormone responsiveness. In addition, we found that these promoters have the transcription factor of B. platyphylla SPL2 (BpSPL2) binding motif GTAC. Expression analysis demonstrated that BpPIF genes, especially BpPIF4, BpPIF9b, and BpPIF10, might be the potential target genes of BpSPL2 in the process of adventitious root formation. Besides providing a comprehensive understanding of the BpPIF family, we propose a hypothetical gene network regulatory model for adventitious root formation.