HYPOCOTYL 5 Research Articles

Investigating the Role of Known Arabidopsis Iron Genes in a Stress Resilient Soybean Line.

Genes involved in iron deficiency responses have been well characterized in Arabidopsis thaliana, but their roles in crop species have not been well explored. Reliance on model species may fail to identify novel iron stress mechanisms present within crop species, likely selected by hundreds of years of selection. Fiskeby III (PI 438471) is a soybean line from Sweden that demonstrates high levels of resilience to numerous stresses. Earlier Fiskeby III studies have identified a suite of genes responding to iron deficiency stress in Fiskeby III that are also associated with Arabidopsis iron deficiency responses. We were interested in determining how canonical iron genes function in Fiskeby III under normal and iron stress conditions. To investigate this, we used virus-induced gene silencing to knock down gene expression of three iron deficiency response genes (FER-like iron deficiency induced transcription factor (FIT), elongated hypocotyl 5 (HY5) and popeye (PYE)) in Fiskeby III. Analyses of RNAseq data generated from silenced plants in iron-sufficient and -deficient conditions found silencing FIT and HY5 altered general stress responses but did not impact iron deficiency tolerance, confirming Fiskeby III utilizes novel mechanisms to tolerate iron deficiency stress.

Arabidopsis B-BOX DOMAIN PROTEIN14/15/16 form a feedback loop with ELONGATED HYPOCOTYL 5 and PHYTOCHROME-INTERACTING FACTORs to regulate hypocotyl elongation

Light-regulated developmental processes such as photomorphogenesis and flowering play important roles in the plant life cycle, from seedling emergence to reproduction. Three members of the Arabidopsis thaliana B-BOX DOMAIN PROTEIN (BBX) family, BBX14, BBX15, and BBX16 (hereafter BBX14/15/16), redundantly regulate flowering time, but whether this genetic redundancy also affects the regulation of photomorphogenesis remains unclear. Here, we show that light induces BBX14/15/16 expression primarily in the hypocotyl, where BBX14/15/16 redundantly repress hypocotyl elongation. PHYTOCHROME-INTERACTING FACTORs (PIFs) negatively regulate BBX14/15/16 expression mainly through GOLDEN-LIKE proteins (GLKs); however, analyses of ChIP-seq data showed that PIFs are recruited to the BBX14/15/16 loci and can also regulate these genes independently of GLKs. ELONGATED HYPOCOTYL 5 (HY5), a major regulator of photomorphogenesis, also directly binds to the BBX14/15/16 loci and regulates their expression. Simultaneous knockdown of BBX14/15/16 resulted in significant downregulation of HY5 and upregulation of PIFs, suggesting that these factors participate in a feedback regulatory loop. Indeed, BBX14/15/16 induced HY5 promoter activity by binding to the HY5 promoter. The brassinosteroid-responsive gene TOUCH4 (TCH4) and several auxin-responsive SMALL AUXIN UPREGULATED RNA (SAUR) genes were upregulated in the BBX14/15/16 knockdown plants, suggesting that auxin and brassinosteroids might participate in BBX14/15/16-mediated hypocotyl regulation. Mutating the predicted BBX-binding sites in SAUR4 and TCH4 impaired their regulation by BBX14/15/16. We propose that BBX14/15/16, together with HY5 and PIFs, form a feedback loop that regulates the expression of auxin- and brassinosteroid-related genes to modulate hypocotyl elongation.

Light signaling-dependent regulation of plastid RNA processing in Arabidopsis.

Light is a vital environmental signal that regulates the expression of plastid genes. Plastids are crucial organelles that respond to light, but the effects of light on plastid RNA processing following transcription remain unclear. In this study, we systematically examined the influence of light exposure on plastid RNA processing, focusing on RNA splicing and RNA editing. We demonstrated that light promotes the splicing of transcripts from the plastid genes rps12, ndhA, atpF, petB, and rpl2. Additionally, light increased the editing rate of the accD transcript at nucleotide 794 (accD-794) and the ndhF transcript at nucleotide 290 (ndhF-290), while decreasing the editing rate of the clpP transcript at nucleotide 559 (clpP-559). We have identified key regulators of signaling pathways, such as CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1), ELONGATED HYPOCOTYL 5 (HY5), and PHYTOCHROME-INTERACTING FACTORs (PIFs), as important players in the regulation of plastid RNA splicing and editing. Notably, COP1 was required for GENOMES UNCOUPLED1 (GUN1)-dependent repression of clpP-559 editing in the light. We showed that HY5 and PIF1 bind to the promoters of nuclear genes encoding plastid-localized RNA processing factors in a light-dependent manner. This study provides insight into the mechanisms underlying light-mediated post-transcriptional regulation of plastid gene expression.

ELONGATED HYPOCOTYL5-mediated light signaling promotes shoot regeneration in Arabidopsis thaliana.

Injured plant somatic tissues regenerate themselves by establishing shoot or root meristems. In Arabidopsis (Arabidopsis thaliana), a two-step culture system ensures regeneration by first promoting the acquisition of pluripotency and subsequently specifying the fate of new meristems. Although previous studies have reported the importance of phytohormones auxin and cytokinin in determining the fate of new meristems, whether and how environmental factors influence this process remains elusive. In this study, we investigated the impact of light signals on shoot regeneration using Arabidopsis hypocotyls as explants. We found that light signals promote shoot regeneration while inhibiting root formation. ELONGATED HYPOCOTYL 5 (HY5), the pivotal transcriptional factor in light signaling, plays a central role in this process by mediating the expression of key genes controlling the fate of new meristems. Specifically, HY5 directly represses root development genes and activates shoot meristem genes, leading to the establishment of shoot progenitor from pluripotent callus. We further demonstrated that the early activation of photosynthesis is critical for shoot initiation, and this is transcriptionally regulated downstream of HY5-dependent pathways. In conclusion, we uncovered the intricate molecular mechanisms by which light signals control the establishment of new meristems through the regulatory network governed by HY5, thus highlighting the influence of light signals on plant developmental plasticity.

REPRESSOR OF UV-B PHOTOMORPHOGENESIS proteins target ABA INSENSITIVE 5 for degradation to promote early plant development.

REPRESSOR OF UV-B PHOTOMORPHOGENESIS 1 (RUP1) and RUP2 are WD-40 domain-containing proteins that have been extensively characterized for their role in UV-B signaling. However, the roles of the RUP proteins outside the canonical UV-signaling pathway are less known. Here, we identify that RUP1 and RUP2 play important roles in ABA signaling to regulate seed germination and early seedling development in Arabidopsis thaliana. Our protein interaction studies confirmed that RUP1 and RUP2 physically interact with ABA INSENSITIVE 5 (ABI5). In the presence of abscisic acid, rup1, rup2 and rup1rup2 exhibited reduced germination and seedling establishment compared to the wild type. Germination and seedling establishment in rup1rup2abi5-8 was similar to abi5-8, suggesting that RUP1 and RUP2 suppress ABA-mediated inhibition of germination and early seedling development in an ABI5-dependent manner. The DDB1-binding WD40 (DWD) protein RUP2 promoted the ubiquitination of ABI5 to regulate its degradation. ABI5, in turn, establishes a negative feedback loop to inhibit the expression of RUP1/RUP2. ABI5 also inhibited the direct binding of ELONGATED HYPOCOTYL 5 (HY5) to the promoters of RUP1 and RUP2 under ABA. This study highlights the coordinated action of RUP1, RUP2, ABI5, and HY5 in regulating early plant development.

Strigolactones positively regulate HY5-dependent autophagy and the degradation of ubiquitinated proteins in response to cold stress in tomato.

Autophagy, involved in protein degradation and amino acid recycling, plays a key role in plant development and stress responses. However, the relationship between autophagy and phytohormones remains unclear. We used diverse methods, including CRISPR/Cas9, ultra-performance liquid chromatography coupled with tandem mass spectrometry, chromatin immunoprecipitation, electrophoretic mobility shift assays, and dual-luciferase assays to explore the molecular mechanism of strigolactones in regulating autophagy and the degradation of ubiquitinated proteins under cold stress in tomato (Solanum lycopersicum). We show that cold stress induced the accumulation of ubiquitinated proteins. Mutants deficient in strigolactone biosynthesis were more sensitive to cold stress with increased accumulation of ubiquitinated proteins. Conversely, treatment with the synthetic strigolactone analog GR245DS enhanced cold tolerance in tomato, with elevated levels of accumulation of autophagosomes and transcripts of autophagy-related genes (ATGs), and reduced accumulation of ubiquitinated proteins. Meanwhile, cold stress induced the accumulation of ELONGATED HYPOCOTYL 5 (HY5), which was triggered by strigolactones. HY5 further trans-activated ATG18a transcription, resulting in autophagy formation. Mutation of ATG18a compromised strigolactone-induced cold tolerance, leading to decreased formation of autophagosomes and increased accumulation of ubiquitinated proteins. These findings reveal that strigolactones positively regulate autophagy in an HY5-dependent manner and facilitate the degradation of ubiquitinated proteins under cold conditions in tomato.

Temporal and spatial frameworks supporting plant responses to vegetation proximity.

After perception of vegetation proximity by phytochrome photoreceptors, shade-avoider plants initiate a set of responses known as the Shade Avoidance Syndrome (SAS). Shade perception by the phytochrome B (phyB) photoreceptor unleashes the PHYTOCHROME INTERACTING FACTORs (PIFs) and initiates SAS responses. In Arabidopsis (Arabidopsis thaliana) seedlings, shade perception involves rapid and massive changes in gene expression, increases auxin production, and promotes hypocotyl elongation. Other components, such as phyA and ELONGATED HYPOCOTYL 5 (HY5), also participate in the shade regulation of the hypocotyl elongation response by repressing it. However, why and how so many regulators with either positive or negative activities modulate the same response remain unclear. Our physiological, genetic, cellular, and transcriptomic analyses showed that (1) these components are organized into two main branches or modules and (2) the connection between them is dynamic and changes with the time of shade exposure. We propose a model for the regulation of shade-induced hypocotyl elongation in which the temporal and spatial functional importance of the various SAS regulators analyzed here helps to explain the co-existence of differentiated regulatory branches with overlapping activities.

ELONGATED HYPOCOTYL 5 (HY5) and POPEYE (PYE) regulate intercellular iron transport in plants.

Plants maintain iron (Fe) homeostasis under varying environmental conditions by balancing processes such as Fe uptake, transportand storage. In Arabidopsis, POPEYE (PYE), a basic helix-loop-helix transcription factor (TF), has been shown to play a crucial role in regulating this balance. In recent years, the mechanisms regulating Fe uptake have been well established but the upstream transcriptional regulators of Fe transport and storage are still poorly understood. In this study, we report that ELONGATED HYPOCOTYL5 (HY5), a basic leucine zipper (bZIP) TF which has recently been shown to play a crucial role in Fe homeostasis, interacts with PYE. Molecular, geneticand biochemical approaches revealed that PYE and HY5 have overlapping as well as some distinct roles in the regulation of Fe deficiency response. We found that HY5 and PYE both act as a repressor of Fe transport genes such as YSL3, FRD3, NPF5.9, YSL2, NAS4and OPT3. HY5 was found to directly bind on the promoter of these genes and regulate intercellular Fe transport. Further analysis revealed that HY5 and PYE directly interact at the same region on PYE and NAS4 promoter. Overall, this study revealed that HY5 regulates Fe homeostasis by physically interacting with PYE as well as independently.

Ubiquitin-specific protease UBP14 stabilizes HY5 by deubiquitination to promote photomorphogenesis in Arabidopsis thaliana

Transcription factor ELONGATED HYPOCOTYL5 (HY5) is the central hub for seedling photomorphogenesis. E3 ubiquitin (Ub) ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) inhibits HY5 protein accumulation through ubiquitination. However, the process of HY5 deubiquitination, which antagonizes E3 ligase-mediated ubiquitination to maintain HY5 homeostasis has never been studied. Here, we identified that Arabidopsis thaliana deubiquitinating enzyme, Ub-SPECIFIC PROTEASE 14 (UBP14) physically interacts with HY5 and enhances its protein stability by deubiquitination. The da3-1 mutant lacking UBP14 function exhibited a long hypocotyl phenotype, and UBP14 deficiency led to the failure of rapid accumulation of HY5 during dark to light. In addition, UBP14 preferred to stabilize nonphosphorylated form of HY5 which is more readily bound to downstream target genes. HY5 promoted the expression and protein accumulation of UBP14 for positive feedback to facilitate photomorphogenesis. Our findings thus established a mechanism by which UBP14 stabilizes HY5 protein by deubiquitination to promote photomorphogenesis in A. thaliana.

A transcriptional cascade involving BBX22 and HY5 finely regulates both plant height and fruit pigmentation in citrus.

Dwarfing is a pivotal agronomic trait affecting both yield and quality. Citrus species exhibit substantial variation in plant height, among which internode length is a core element. However, the molecular mechanism governing internode elongation remains unclear. Here, we unveiled that the transcriptional cascade consisting of B-BOX DOMAIN PROTEIN 22 (BBX22) and ELONGATED HYPOCOTYL 5 (HY5) finely tunes plant height and internode elongation in citrus. Loss-of-function mutations of BBX22 in an early-flowering citrus (Citrus hindsii "SJG") promoted internode elongation and reduced pigment accumulation, whereas ectopic expression of BBX22 in SJG, sweet orange (C. sinensis), pomelo (C. maxima) or heterologous expression of BBX22 in tomato (Solanum lycopersicum) significantly decreased internode length. Furthermore, exogenous application of gibberellin A3 (GA3) rescued the shortened internode and dwarf phenotype caused by BBX22 overexpression. Additional experiments revealed that BBX22 played a dual role in regulation internode elongation and pigmentation in citrus. On the one hand, it directly bound to and activated the expression of HY5, GA metabolism gene (GA2 OXIDASE 8, GA2ox8), carotenoid biosynthesis gene (PHYTOENE SYNTHASE 1, PSY1) and anthocyanin regulatory gene (Ruby1, a MYB DOMAIN PROTEIN). On the other hand, it acted as a cofactor of HY5, enhancing the ability of HY5 to regulate target genes expression. Together, our results reveal the critical role of the transcriptional cascade consisting of BBX22 and HY5 in controlling internode elongation and pigment accumulation in citrus. Unraveling the crosstalk regulatory mechanism between internode elongation and fruit pigmentation provides key genes for breeding of novel types with both dwarf and health-beneficial fortification in citrus.

Maize ZmSRO1e promotes mesocotyl elongation and deep sowing tolerance by inhibiting the activity of ZmbZIP61.

Deep sowing is a traditional method for drought resistance in maize production, and mesocotyl elongation is strongly associated with the ability of maize to germinate from deep soil. However, little is known about the functional genes and mechanisms regulating maize mesocotyl elongation. In the present study, we identified a plant-specific SIMILAR TO RCD-ONE (SRO) protein family member, ZmSRO1e, involved in maize mesocotyl elongation. The expression of ZmSRO1e is strongly inhibited upon transfer from dark to white light. The loss-of-function zmsro1e mutant exhibited a dramatically shorter mesocotyl than the wild-type in both constant light and darkness, while overexpression of ZmSRO1e significantly promoted mesocotyl elongation, indicating that ZmSRO1e positively regulates mesocotyl elongation. We showed that ZmSRO1e physically interacted with ZmbZIP61, an ortholog of Arabidopsis ELONGATED HYPOCOTYL 5 (HY5) and showed a function similar to that of HY5 in regulating photomorphogenesis. We found that ZmSRO1e repressed the transcriptional activity of ZmbZIP61 toward target genes involved in the regulation of cell expansion, such as ZmEXPB4 and ZmEXPB6, by interfering with the binding of ZmbZIP61 to the promoters of target genes. Our results provide a new understanding of the mechanism by which SRO regulates photomorphogenesis and highlight its potential application in deep sowing-resistant breeding.

Organ-specific transcriptional regulation by HFR1 and HY5 in response to shade in Arabidopsis.

Light is crucial for plants and serves as a signal for modulating their growth. Under shade, where red to far-red light ratio is low, plants exhibit shade avoidance responses (SAR). LONG HYPOCOTYL IN FAR-RED 1 (HFR1) and ELONGATED HYPOCOTYL 5 (HY5) are known to be negative regulators of SAR and physically interact with one another. However, transcriptional regulatory network underlying SAR by these two transcription factors has not been explored. Here, we performed organ-specific transcriptome analyses of Arabidopsis thaliana hfr1-5, hy5-215 and hfr1hy5 to identify genes that are co-regulated by HFR1 and HY5 in hypocotyls and cotyledons. Genes co-regulated by HFR1 and HY5 were enriched in various processes related to cell wall modification and chlorophyll biosynthesis in hypocotyls. Phytohormone (abscisic acid and jasmonic acid) and light responses were significantly regulated by HFR1 and HY5 in both organs, though it is more prominent under shade in cotyledons. HFR1 and HY5 also differentially regulate the expression of the cell wall-related genes for xyloglucan endotransglucosylase/hydrolase, expansin, arabinogalactan protein and class III peroxidase depending on the organs. Furthermore, HFR1 and HY5 cooperatively regulated hypocotyl responsiveness to shade through auxin metabolism. Together, our study illustrates the importance of the HFR1-HY5 module in regulating organ-specific shade responses in Arabidopsis.

The Complex FtBBX22 and FtHY5 Positively Regulates Light-Induced Anthocyanin Accumulation by Activating FtMYB42 in Tartary Buckwheat Sprouts.

Anthocyanin is one important nutrition composition in Tartary buckwheat (Fagopyrum tataricum) sprouts, a component missing in its seeds. Although anthocyanin biosynthesis requires light, the mechanism of light-induced anthocyanin accumulation in Tartary buckwheat is unclear. Here, comparative transcriptome analysis of Tartary buckwheat sprouts under light and dark treatments and biochemical approaches were performed to identify the roles of one B-box protein BBX22 and ELONGATED HYPOCOTYL 5 (HY5). The overexpression assay showed that FtHY5 and FtBBX22 could both promote anthocyanin synthesis in red-flower tobacco. Additionally, FtBBX22 associated with FtHY5 to form a complex that activates the transcription of MYB transcription factor genes FtMYB42 and FtDFR, leading to anthocyanin accumulation. These findings revealed the regulation mechanism of light-induced anthocyanin synthesis and provide excellent gene resources for breeding high-quality Tartary buckwheat.

GIBBERELLIN PERCEPTION SENSOR 2 reveals genesis and role of cellular GA dynamics in light-regulated hypocotyl growth.

The phytohormone gibberellic acid (GA) is critical for environmentally sensitive plant development including germination, skotomorphogenesis, and flowering. The Förster resonance energy transfer biosensor GIBBERELLIN PERCEPTION SENSOR1, which permits single-cell GA measurements in vivo, has been used to observe a GA gradient correlated with cell length in dark-grown, but not light-grown, hypocotyls. We sought to understand how light signaling integrates into cellular GA regulation. Here, we show how the E3 ligase CONSTITUTIVE PHOTOMORPHOGENESIS1 (COP1) and transcription factor ELONGATED HYPOCOTYL 5 (HY5) play central roles in directing cellular GA distribution in skoto- and photomorphogenic hypocotyls, respectively. We demonstrate that the expression pattern of the GA biosynthetic enzyme gene GA20ox1 is the key determinant of the GA gradient in dark-grown hypocotyls and is a target of COP1 signaling. We engineered a second generation GPS2 biosensor with improved orthogonality and reversibility. GPS2 revealed a previously undetectable cellular pattern of GA depletion during the transition to growth in the light. This GA depletion partly explains the resetting of hypocotyl growth dynamics during photomorphogenesis. Achieving cell-level resolution has revealed how GA distributions link environmental conditions with morphology and morphological plasticity. The GPS2 biosensor is an ideal tool for GA studies in many conditions, organs, and plant species.

Light signaling regulates root-knot nematode infection and development via HY5-SWEET signaling

BackgroundMeloidogyne incognita is one of the most important plant-parasitic nematodes and causes tremendous losses to the agricultural economy. Light is an important living factor for plants and pathogenic organisms, and sufficient light promotes root-knot nematode infection, but the underlying mechanism is still unclear.ResultsExpression level and genetic analyses revealed that the photoreceptor genes PHY, CRY, and PHOT have a negative impact on nematode infection. Interestingly, ELONGATED HYPOCOTYL5 (HY5), a downstream gene involved in the regulation of light signaling, is associated with photoreceptor-mediated negative regulation of root-knot nematode resistance. ChIP and yeast one-hybrid assays supported that HY5 participates in plant-to-root-knot nematode responses by directly binding to the SWEET negative regulatory factors involved in root-knot nematode resistance.ConclusionsThis study elucidates the important role of light signaling pathways in plant resistance to nematodes, providing a new perspective for RKN resistance research.

The AaBBX21-AaHY5 module mediates light-regulated artemisinin biosynthesis in Artemisia annua L.

The sesquiterpene lactone artemisinin is an important anti-malarial component produced by the glandular secretory trichomes of sweet wormwood (Artemisia annua L.). Light was previously shown to promote artemisinin production, but the underlying regulatory mechanism remains elusive. In this study, we demonstrate that ELONGATED HYPOCOTYL 5 (HY5), a central transcription factor in the light signaling pathway, cannot promote artemisinin biosynthesis on its own, as the binding of AaHY5 to the promoters of artemisinin biosynthetic genes failed to activate their transcription. Transcriptome analysis and yeast two-hybrid screening revealed the B-box transcription factor AaBBX21 as a potential interactor with AaHY5. AaBBX21 showed a trichome-specific expression pattern. Additionally, the AaBBX21-AaHY5 complex cooperatively activated transcription from the promoters of the downstream genes AaGSW1, AaMYB108, and AaORA, encoding positive regulators of artemisinin biosynthesis. Moreover, AaHY5 and AaBBX21 physically interacted with the A. annua E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). In the dark, AaCOP1 decreased the accumulation of AaHY5 and AaBBX21 and repressed the activation of genes downstream of the AaHY5-AaBBX21 complex, explaining the enhanced production of artemisinin upon light exposure. Our study provides insights into the central regulatory mechanism by which light governs terpenoid biosynthesis in the plant kingdom.

HY5 and COP1 function antagonistically in the regulation of nicotine biosynthesis in Nicotiana tabacum

Nicotine constitutes approximately 90% of the total alkaloid content in leaves within the Nicotiana species, rendering it the most prevalent alkaloid. While the majority of genes responsible for nicotine biosynthesis express in root tissue, the influence of light on this process through shoot-to-root mobile ELONGATED HYPOCOTYL 5 (HY5) has been recognized. CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1), a key regulator of light-associated responses, known for its role in modulating HY5 accumulation, remains largely unexplored in its relationship to light-dependent nicotine accumulation. Here, we identified NtCOP1, a COP1 homolog in Nicotiana tabacum, and demonstrated its ability to complement the cop1-4 mutant in Arabidopsis thaliana at molecular, morphological, and biochemical levels. Through the development of NtCOP1 overexpression (NtCOP1OX) plants, we observed a significant reduction in nicotine and flavonol content, inversely correlated with the down-regulation of nicotine and phenylpropanoid pathway. Conversely, CRISPR/Cas9-based knockout mutant plants (NtCOP1CR) exhibited an increase in nicotine levels. Further investigations, including yeast-two hybrid assays, grafting experiments, and Western blot analyses, revealed that NtCOP1 modulates nicotine biosynthesis by targeting NtHY5, thereby impeding its transport from shoot-to-root. We conclude that the interplay between HY5 and COP1 functions antagonistically in the light-dependent regulation of nicotine biosynthesis in tobacco.

The SMXL8-AGL9 module mediates crosstalk between strigolactone and gibberellin to regulate strigolactone-induced anthocyanin biosynthesis in apple.

Although the strigolactone (SL) signaling pathway and SL-mediated anthocyanin biosynthesis have been reported, the molecular association between SL signaling and anthocyanin biosynthesis remains unclear. In this study, we identified the SL signal transduction pathway associated with anthocyanin biosynthesis and the crosstalk between gibberellin (GA) and SL signaling in apple (Malus × domestica). ELONGATED HYPOCOTYL5 (HY5) acts as a key node integrating SL signaling and anthocyanin biosynthesis, and the SL-response factor AGAMOUS-LIKE MADS-BOX9 (AGL9) promotes anthocyanin biosynthesis by activating HY5 transcription. The SL signaling repressor SUPPRESSOR OF MAX2 1-LIKE8 (SMXL8) interacts with AGL9 to form a complex that inhibits anthocyanin biosynthesis by downregulating HY5 expression. Moreover, the E3 ubiquitin ligase PROTEOLYSIS1 (PRT1) mediates the ubiquitination-mediated degradation of SMXL8, which is a key part of the SL signal transduction pathway associated with anthocyanin biosynthesis. In addition, the GA signaling repressor REPRESSOR-of-ga1-3-LIKE2a (RGL2a) mediates the crosstalk between GA and SL by disrupting the SMXL8-AGL9 interaction that represses HY5 transcription. Taken together, our study reveals the regulatory mechanism of SL-mediated anthocyanin biosynthesis and uncovers the role of SL-GA crosstalk in regulating anthocyanin biosynthesis in apple.

HY5 and PIF antagonistically regulate HMGR expression and sterol biosynthesis in Arabidopsis thaliana

Secondary metabolites play multiple crucial roles in plants by modulating various regulatory networks. The biosynthesis of these compounds is unique to each species and is intricately controlled by a range of developmental and environmental factors. While light's role in certain secondary metabolites is evident, its impact on sterol biosynthesis remains unclear. Previous studies indicate that ELONGATED HYPOCOTYL5 (HY5), a bZIP transcription factor, is pivotal in skotomorphogenesis to photomorphogenesis transition. Additionally, PHYTOCHROME INTERACTING FACTORs (PIFs), bHLH transcription factors, act as negative regulators. To unveil the light-dependent regulation of the mevalonic acid (MVA) pathway, a precursor for sterol biosynthesis, mutants of light signaling components, specifically hy5–215 and the pifq quadruple mutant (pif 1,3,4, and 5), were analyzed in Arabidopsis thaliana. Gene expression analysis in wild-type and mutants implicates HY5 and PIFs in regulating sterol biosynthesis genes. DNA-protein interaction analysis confirms their interaction with key genes like AtHMGR2 in the rate-limiting pathway. Results strongly suggest HY5 and PIFs' pivotal role in light-dependent MVA pathway regulation, including the sterol biosynthetic branch, in Arabidopsis, highlighting a diverse array of light signaling components finely tuning crucial growth pathways.

Nutrient levels control root growth responses to high ambient temperature in plants

Global warming will lead to significantly increased temperatures on earth. Plants respond to high ambient temperature with altered developmental and growth programs, termed thermomorphogenesis. Here we show that thermomorphogenesis is conserved in Arabidopsis, soybean, and rice and that it is linked to a decrease in the levels of the two macronutrients nitrogen and phosphorus. We also find that low external levels of these nutrients abolish root growth responses to high ambient temperature. We show that in Arabidopsis, this suppression is due to the function of the transcription factor ELONGATED HYPOCOTYL 5 (HY5) and its transcriptional regulation of the transceptor NITRATE TRANSPORTER 1.1 (NRT1.1). Soybean and Rice homologs of these genes are expressed consistently with a conserved role in regulating temperature responses in a nitrogen and phosphorus level dependent manner. Overall, our data show that root thermomorphogenesis is a conserved feature in species of the two major groups of angiosperms, monocots and dicots, that it leads to a reduction of nutrient levels in the plant, and that it is dependent on environmental nitrogen and phosphorus supply, a regulatory process mediated by the HY5-NRT1.1 module.