RESUMO
Major constituents of the plant cell walls are structural proteins that belong to the hydroxyproline-rich glycoprotein (HRGP) family. Leucine-rich repeat extensin (LRX) proteins contain a leucine-rich domain and a C-terminal domain with repetitive Ser-Pro3-5 motifs that are potentially to be O-glycosylated. It has been demonstrated that pollen-specific LRX8-LRX11 from Arabidopsis thaliana are necessary to maintain the integrity of the pollen tube cell wall during polarized growth. In HRGPs, including classical extensins (EXTs), and probably in LRXs, proline residues are converted to hydroxyproline by prolyl-4-hydroxylases (P4Hs), thus defining novel O-glycosylation sites. In this context, we aimed to determine whether hydroxylation and subsequent O-glycosylation of Arabidopsis pollen LRXs are necessary for their proper function and cell wall localization in pollen tubes. We hypothesized that pollen-expressed P4H4 and P4H6 catalyze the hydroxylation of the proline units present in Ser-Pro3-5 motifs of LRX8-LRX11. Here, we show that the p4h4-1 p4h6-1 double mutant exhibits a reduction in pollen germination rates and a slight reduction in pollen tube length. Pollen germination is also inhibited by P4H inhibitors, suggesting that prolyl hydroxylation is required for pollen tube development. Plants expressing pLRX11::LRX11-GFP in the p4h4-1 p4h6-1 background show partial re-localization of LRX11-green fluorescent protein (GFP) from the pollen tube tip apoplast to the cytoplasm. Finally, immunoprecipitation-tandem mass spectrometry analysis revealed a decrease in oxidized prolines (hydroxyprolines) in LRX11-GFP in the p4h4-1 p4h6-1 background compared with lrx11 plants expressing pLRX11::LRX11-GFP. Taken together, these results suggest that P4H4 and P4H6 are required for pollen germination and for proper hydroxylation of LRX11 necessary for its localization in the cell wall of pollen tubes.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Tubo Polínico , Prolil Hidroxilases , Arabidopsis/metabolismo , Arabidopsis/genética , Hidroxilação , Tubo Polínico/crescimento & desenvolvimento , Tubo Polínico/metabolismo , Tubo Polínico/genética , Proteínas de Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Prolil Hidroxilases/metabolismo , Prolil Hidroxilases/genética , Parede Celular/metabolismoRESUMO
Mediator is a large multiprotein complex that is required for the transcription of most, if not all, genes transcribed by RNA Polymerase II. A core set of subunits is essential to assemble a functional Mediator in vitro and, therefore, the corresponding loss-of-function mutants are expected to be lethal. The MED30 subunit is essential in animal systems, but is absent in yeast. Here, we report that MED30 is also essential for both male gametophyte and embryo development in the model plant Arabidopsis thaliana Mutant med30 pollen grains were viable and some were able to germinate and target the ovules, although the embryos aborted shortly after fertilization, suggesting that MED30 is important for the paternal control of early embryo development. When gametophyte defects were bypassed by specific pollen complementation, loss of MED30 led to early embryo development arrest. Later in plant development, MED30 promotes flowering through multiple signaling pathways; its downregulation led to a phase change delay, downregulation of SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 3 (SPL3), FLOWERING LOCUS T (FTI) and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), and upregulation of FLOWERING LOCUS C (FLC).
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Flores/metabolismo , Arabidopsis/genética , Arabidopsis/fisiologia , Proteínas de Arabidopsis/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Flores/genética , Flores/fisiologia , Regulação da Expressão Gênica de Plantas/genética , Regulação da Expressão Gênica de Plantas/fisiologia , Proteínas de Domínio MADS/genética , Proteínas de Domínio MADS/metabolismo , Desenvolvimento Vegetal/genética , Desenvolvimento Vegetal/fisiologia , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The pollen and pistil RALF peptides, along with multiple receptor-like kinases and leucine-rich repeat extensins, regulate pollen tube growth and the final burst within the ovule, where sperm cells are released for fertilisation to occur. This review introduces some new questions that arose about the regulation of this complex process.
Assuntos
Proteínas de Arabidopsis , Arabidopsis , Peptídeos , Pólen , Tubo PolínicoRESUMO
As sessile organisms, plants have evolved mechanisms to adapt to variable and rapidly fluctuating environmental conditions. Calcium (Ca2+) in plant cells is a versatile intracellular second messenger that is essential for stimulating short- and long-term responses to environmental stresses through changes in its concentration in the cytosol ([Ca2+]cyt). Increases in [Ca2+]cyt direct the strength and length of these stimuli. In order to terminate them, the cells must then remove the cytosolic Ca2+ against a concentration gradient, either taking it away from the cell or storing it in organelles such as the endoplasmic reticulum (ER) and/or vacuoles. Here, we review current knowledge about the biological roles of plant P-type Ca2+-ATPases as potential actors in the regulation of this cytosolic Ca2+ efflux, with a focus the IIA ER-type Ca2+-ATPases (ECAs) and the IIB autoinhibited Ca2+-ATPases (ACAs). While ECAs are analogous proteins to animal sarcoplasmic-endoplasmic reticulum Ca2+-ATPases (SERCAs), ACAs are equivalent to animal plasma membrane-type ATPases (PMCAs). We examine their expression patterns in cells exhibiting polar growth and consider their appearance during the evolution of the plant lineage. Full details of the functions and coordination of ECAs and ACAs during plant growth and development have not yet been elucidated. Our current understanding of the regulation of fluctuations in Ca2+ gradients in the cytoplasm and organelles during growth is in its infancy, but recent technological advances in Ca2+ imaging are expected to shed light on this subject.
Assuntos
ATPases Transportadoras de Cálcio , Cálcio , Desenvolvimento Vegetal , Plantas/enzimologia , Cálcio/metabolismo , ATPases Transportadoras de Cálcio/metabolismo , Retículo Endoplasmático/metabolismoRESUMO
In recent years it has become clear that there are several molecular links that interconnect the plant cell surface continuum, which is highly important in many biological processes such as plant growth, development, and interaction with the environment. The plant cell surface continuum can be defined as the space that contains and interlinks the cell wall, plasma membrane and cytoskeleton compartments. In this review, we provide an updated view of cell surface proteins that include modular domains with an extensin (EXT)-motif followed by a cytoplasmic kinase-like domain, known as PERKs (for proline-rich extensin-like receptor kinases); with an EXT-motif and an actin binding domain, known as formins; and with extracellular hybrid-EXTs. We focus our attention on the EXT-motifs with the short sequence Ser-Pro(3-5), which is found in several different protein contexts within the same extracellular space, highlighting a putative conserved structural and functional role. A closer understanding of the dynamic regulation of plant cell surface continuum and its relationship with the downstream signalling cascade is a crucial forthcoming challenge.
Assuntos
Glicoproteínas/química , Proteínas de Membrana/química , Proteínas de Plantas/química , Motivos de Aminoácidos , Parede Celular/química , Plantas/química , Prolina/química , Proteínas Quinases/químicaRESUMO
While studying blue light-independent effects of cryptochrome 1 (cry1) photoreceptor, we observed premature opening of the hook in cry1 mutants grown in complete darkness, a phenotype that resembles the one described for the heterotrimeric G-protein α subunit (GPA1) null mutant gpa1. Both cry1 and gpa1 also showed reduced accumulation of anthocyanin under blue light. These convergent gpa1 and cry1 phenotypes required the presence of sucrose in the growth media and were not additive in the cry1 gpa1 double mutant, suggesting context-dependent signaling convergence between cry1 and GPA1 signaling pathways. Both, gpa1 and cry1 mutants showed reduced GTP-binding activity. The cry1 mutant showed wild-type levels of GPA1 mRNA or GPA1 protein. However, an anti-transducin antibody (AS/7) typically used for plant Gα proteins, recognized a 54 kDa band in the wild type but not in gpa1 and cry1 mutants. We propose a model where cry1-mediated post-translational modification of GPA1 alters its GTP-binding activity.
Assuntos
Antocianinas/metabolismo , Proteínas de Arabidopsis/genética , Arabidopsis/genética , Criptocromos/genética , Subunidades alfa de Proteínas de Ligação ao GTP/genética , Processamento de Proteína Pós-Traducional , Transdução de Sinais/genética , Antocianinas/análise , Antocianinas/biossíntese , Arabidopsis/efeitos dos fármacos , Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/metabolismo , Criptocromos/metabolismo , Subunidades alfa de Proteínas de Ligação ao GTP/metabolismo , Regulação da Expressão Gênica de Plantas/fisiologia , Hipocótilo/efeitos dos fármacos , Hipocótilo/genética , Hipocótilo/fisiologia , Hipocótilo/efeitos da radiação , Luz , Modelos Biológicos , Mutação , Fenótipo , Ligação Proteica , RNA Mensageiro/genética , RNA de Plantas/genética , Plântula/efeitos dos fármacos , Plântula/genética , Plântula/fisiologia , Plântula/efeitos da radiação , Sacarose/farmacologiaRESUMO
Proline-rich extensin-like receptor kinases (PERKs) belong to the hydroxyproline-rich glycoprotein (HRGP) superfamily known to be involved in many plant developmental processes. Here, we characterized two pollen-expressed PERKs from Arabidopsis thaliana, PERK5 and PERK12. Pollen tube growth was impaired in single and double perk5-1 perk12-1 loss of function mutants, with an impact on seed production. When the segregation was analysed, a male gametophytic defect was found, indicating that perk5-1 and perk12-1 mutants carry deficient pollen transmission. Furthermore, perk5-1 perk12-1 displayed an excessive accumulation of pectins and cellulose at the cell wall of the pollen tubes. Our results indicate that PERK5 and PERK12 are necessary for proper pollen tube growth, highlighting their role in cell wall assembly and reactive oxygen species homeostasis.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Tubo Polínico/crescimento & desenvolvimento , Prolina/metabolismo , Proteínas Quinases/metabolismo , Espécies Reativas de Oxigênio/metabolismoRESUMO
BACKGROUND: LePRK1 and LePRK2 are two pollen receptor kinases localized to the plasma membrane, where they are present in a high molecular weight complex (LePRK complex). LePRK2 is phosphorylated in mature and germinated pollen, but is dephosphorylated when pollen membranes are incubated with tomato or tobacco style extracts. RESULTS: Here we show that LePRK2 dephosphorylation is mediated by a heat-, acid-, base-, DTT- and protease-resistant component from tobacco styles. Using LePRK2 phosphorylation as a tracking assay for purification, style exudates were subjected to chloroform extraction, anionic exchange, and C18 reverse-phase chromatography columns. We finally obtained a single ~3,550 Da compound (as determined by UV-MALDI-TOF MS) that we named STIL (for Style Interactor for LePRKs). STIL increased pollen tube lengths of in vitro germinated pollen in a dose-dependent manner. CONCLUSION: We propose that the LePRK complex perceives STIL, resulting in LePRK2 dephosphorylation and an increase in pollen tube growth.
Assuntos
Proteínas de Plantas/metabolismo , Tubo Polínico/crescimento & desenvolvimento , Proteína Quinase C/metabolismo , Solanum lycopersicum/genética , Solanum lycopersicum/crescimento & desenvolvimento , Solanum lycopersicum/metabolismo , Fosforilação , Proteínas de Plantas/genética , Proteínas de Plantas/isolamento & purificaçãoRESUMO
Serine/arginine-rich (SR) proteins are important regulators of mRNA splicing. Several postsplicing activities have been described for a subset of shuttling SR proteins, including regulation of mRNA export and translation. Using the fibronectin gene to study the links between signal-transduction pathways and SR protein activity, we show that growth factors not only modify the alternative splicing pattern of the fibronectin gene but also alter translation of reporter messenger RNAs in an SR protein-dependent fashion, providing two coregulated levels of isoform-specific amplification. These effects are inhibited by specific small interfering RNAs against SR proteins and are mediated by the AKT kinase, which elicits opposite effects to those evoked by overexpressing SR protein kinases Clk and SRPK. These results show how SR protein activity is modified in response to extracellular stimulation, leading to a concerted regulation of splicing and translation.
Assuntos
Proteínas Nucleares/metabolismo , Fosfoproteínas/metabolismo , Biossíntese de Proteínas/genética , Proteínas Proto-Oncogênicas c-akt/metabolismo , Splicing de RNA , Sequência de Aminoácidos , Animais , Núcleo Celular/química , Núcleo Celular/metabolismo , Citoplasma/química , Citoplasma/metabolismo , Fibronectinas/genética , Substâncias de Crescimento/metabolismo , Humanos , Dados de Sequência Molecular , Proteínas Nucleares/análise , Proteínas Nucleares/genética , Fosfatidilinositol 3-Quinases/metabolismo , Fosfoproteínas/análise , Fosfoproteínas/genética , Biossíntese de Proteínas/efeitos dos fármacos , RNA Mensageiro/metabolismo , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/farmacologia , Proteínas de Ligação a RNA , Fatores de Processamento de Serina-Arginina , Transdução de SinaisRESUMO
To achieve fertilization, pollen tubes have to protect and properly deliver sperm cells through the pistil to the ovules. Pollen tube growth is a representative example of polarized growth where new components of the cell wall and plasma membrane are continuously deposited at the tip of the growing cell. The integrity of the cell wall is of fundamental importance to maintain apical growth. For this reason, pollen tube growth has become an excellent model to study the role of polysaccharides and structural cell wall proteins involved in polar cell expansion. However, quantification of structural polysaccharides at the pollen tube cell wall has been challenging due to technical complexity and the difficulty of finding specific dyes. Here, we propose simple methods for imaging and quantification of callose, pectin , and cellulose using specific dyes such as Aniline Blue, Propidium Iodide, and Pontamine Fast Scarlet 4B.
Assuntos
Parede Celular/metabolismo , Celulose/análise , Glucanos/análise , Pectinas/análise , Tubo Polínico/metabolismo , Coloração e Rotulagem/métodos , Arabidopsis , Parede Celular/química , Microscopia de Fluorescência/métodos , Tubo Polínico/citologiaRESUMO
Pollination includes processes where water and/or solute movements must be finely regulated, suggesting participation of aquaporins. Using information available from different transcriptional profilings of Arabidopsis thaliana mature pollen, we showed that the only aquaporins that are selectively and highly expressed in mature pollen are two TIPs: AtTIP1;3 and AtTIP5;1. Pollen exhibited a lower number and more exclusive type of aquaporin expressed genes when compared to other single cell transcriptional profilings. When characterized using Xenopus oocyte swelling assays, AtTIP1;3 and AtTIP5;1 showed intermediate water permeabilities. Although they displayed neither glycerol nor boric acid permeability they both transported urea. In conclusion, these results suggest a function for AtTIP1;3 and AtTIP5;1 as specific water and urea channels in Arabidopsis pollen.
Assuntos
Aquaporinas/metabolismo , Proteínas de Arabidopsis/biossíntese , Arabidopsis/metabolismo , Pólen/metabolismo , Ureia/metabolismo , Água/metabolismo , Animais , Aquaporinas/biossíntese , Aquaporinas/genética , Proteínas de Arabidopsis/genética , Transporte Biológico/genética , Regulação da Expressão Gênica de Plantas , Transcrição Gênica , XenopusRESUMO
Successful fertilization depends on active molecular dialogues that the male gametophyte can establish with the pistil and the female gametophyte. Pollen grains and stigmas must recognize each other; pollen tubes need to identify the pistil tissues they will penetrate, follow positional cues to exit the transmitting tract and finally, locate the ovules. These molecular dialogues directly affect pollen tube growth rate and orientation. Receptor-like kinases (RLKs) are natural candidates for the perception and decoding of extracellular signals and their transduction to downstream cytoplasmic interactors. Here, we update knowledge regarding how RLKs are involved in pollen tube growth, cell wall integrity and guidance. In addition, we use public data to build a pollen tube RLK interactome that might help direct experiments to elucidate the function of pollen RLKs and their associated proteins.
Assuntos
Arabidopsis/enzimologia , Tubo Polínico/enzimologia , Proteínas Serina-Treonina Quinases/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Flores/enzimologia , Flores/genética , Flores/crescimento & desenvolvimento , Óvulo Vegetal/enzimologia , Óvulo Vegetal/genética , Óvulo Vegetal/crescimento & desenvolvimento , Pólen/enzimologia , Pólen/genética , Pólen/crescimento & desenvolvimento , Tubo Polínico/genética , Tubo Polínico/crescimento & desenvolvimento , Polinização , Proteínas Serina-Treonina Quinases/genética , Receptores de Superfície Celular/genética , Receptores de Superfície Celular/metabolismoRESUMO
Proper cell wall assembly is crucial during pollen tube growth. Leucine-rich repeat extensins (LRXs) are extracellular glycoproteins which belong to the hydroxyproline-rich glycoprotein (HRGP) family. They contain a conserved N-terminal leucine-rich repeat (LRR) domain and a highly variable C-terminal extensin domain. Here, we characterized four LRX proteins (LRX8 through LRX11) from pollen of Arabidopsis thaliana. To investigate the role of LRX8-LRX11 in pollen germination and pollen tube growth, multiple T-DNA lrx mutants were obtained. The lrx mutants display abnormal pollen tubes with an irregular deposition of callose and pectin. They also show serious alterations in pollen germination and segregation ratio. Our results suggest that LRXs are involved in ensuring proper cell wall assembly during pollen tube growth.
Assuntos
Arabidopsis/crescimento & desenvolvimento , Parede Celular/fisiologia , Glicoproteínas/genética , Proteínas de Plantas/genética , Tubo Polínico/crescimento & desenvolvimento , Arabidopsis/genética , Clonagem Molecular , Regulação da Expressão Gênica no Desenvolvimento , Regulação da Expressão Gênica de Plantas , Germinação , Glucanos/metabolismo , Mutagênese Insercional , Pectinas/metabolismo , Tubo Polínico/genéticaRESUMO
The budding yeast Saccharomyces cerevisiae is a useful system to express recombinant proteins and analyze protein-protein interaction. Membrane-spanning proteins like plant receptor kinases find their way to the plasma membrane when expressed in yeast and seem to retain their structure and function. Here, we describe a general yeast DNA transformation procedure based on lithium acetate, salmon sperm DNA, and polyethylene glycol used to express recombinant proteins. Yeast cells expressing plant receptor kinases can be used for in vivo and in vitro studies of receptor function.
Assuntos
Clonagem Molecular/métodos , Vetores Genéticos/metabolismo , Proteína Quinase C/genética , Saccharomyces cerevisiae/genética , Solanum lycopersicum/química , Acetatos/farmacologia , Western Blotting/métodos , DNA de Cadeia Simples/genética , DNA de Cadeia Simples/metabolismo , Eletroforese em Gel de Poliacrilamida/métodos , Galactoquinase/genética , Galactoquinase/metabolismo , Expressão Gênica/efeitos dos fármacos , Vetores Genéticos/química , Isoenzimas/biossíntese , Isoenzimas/genética , Solanum lycopersicum/enzimologia , Solanum lycopersicum/genética , Fases de Leitura Aberta , Polietilenoglicóis/farmacologia , Regiões Promotoras Genéticas , Domínios Proteicos , Proteína Quinase C/biossíntese , Proteínas Recombinantes de Fusão/biossíntese , Proteínas Recombinantes de Fusão/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Transformação GenéticaRESUMO
In order to comprehend the function of a particular protein, identification of the interacting protein partners is a useful approach. Co-immunoprecipitation (Co-IP) is employed to test physical interactions between proteins. Specific antibodies or antibodies against tagged versions can be used to immunoprecipitate the proteins. In this chapter, we describe a method to carry out Co-IP using recombinant membrane proteins expressed in yeast microsomal fractions.
Assuntos
Anticorpos/química , Imunoprecipitação/métodos , Mapeamento de Interação de Proteínas/métodos , Proteína Quinase C/isolamento & purificação , Solanum lycopersicum/genética , Western Blotting , Eletroforese em Gel de Poliacrilamida , Expressão Gênica , Isoenzimas/genética , Isoenzimas/isolamento & purificação , Isoenzimas/metabolismo , Ligantes , Solanum lycopersicum/enzimologia , Microssomos/química , Ligação Proteica , Proteína Quinase C/genética , Proteína Quinase C/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Saccharomyces cerevisiae/química , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismoRESUMO
Many of mRNAs synthesized during pollen development are translated after germination, and we hypothesize that they are stored in cytoplasmic granules. We analyzed the cellular localization of the SKS14 and AT59 Arabidopsis mRNAs, which are orthologues of the tobacco NTP303 and tomato LAT59 pollen mRNAs, respectively, by artificially labeling the transcripts with a MS2-GFP chimera. A MATLAB-automated image analysis helped to identify the presence of cytoplasmic SKS14 and AT59 mRNA granules in mature pollen grains. These mRNA granules partially colocalized with VCS and DCP1, two processing body (PB) proteins. Finally, we found a temporal correlation between SKS14 protein accumulation and the disappearance of SKS14 mRNA granules during pollen germination. These results contribute to unveil a mechanism for translational regulation in Arabidopsis thaliana pollen.
RESUMO
The communication of changes in the extracellular matrix to the interior of the cell is crucial for a cell's function. The extracellular peptides of the RAPID ALKALINIZATION FACTOR (RALF) family have been identified as ligands of receptor-like kinases of the CrRLK1L subclass, but the exact mechanism of their perception is unclear. We found that Arabidopsis RALF4 and RALF19 redundantly regulate pollen tube integrity and growth, and that their function depends on pollen-expressed proteins of the LEUCINE-RICH REPEAT EXTENSIN (LRX) family, which play a role in cell wall development but whose mode of action is not understood. The LRX proteins interact with RALFs, monitoring cell wall changes, which are communicated to the interior of the pollen tube via the CrRLK1L pathway to sustain normal growth.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/crescimento & desenvolvimento , Proteínas de Transporte/metabolismo , Tubo Polínico/crescimento & desenvolvimento , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Transporte/genética , Parede Celular/metabolismo , Peptídeos/genética , Peptídeos/metabolismo , Tubo Polínico/metabolismo , Proteínas Quinases/metabolismoRESUMO
In the recent years, the biophysical properties and presumed physiological role of aquaporins (AQPs) have been expanded to specialized cells where water and solute exchange are crucial traits. Complex but unique processes such as stomatal movement or pollen hydration and germination have been addressed not only by identifying the specific AQP involved but also by studying how these proteins integrate and coordinate cellular activities and functions. In this review, we referred specifically to pollen-specific AQPs and analyzed what has been assumed in terms of transport properties and what has been found in terms of their physiological role. Unlike that in many other cells, the AQP machinery in mature pollen lacks plasma membrane intrinsic proteins, which are extensively studied for their high water capacity exchange. Instead, a variety of TIPs and NIPs are expressed in pollen. These findings have altered the initial understanding of AQPs and water exchange to consider specific and diverse solutes that might be critical to sustaining pollen's success. The spatial and temporal distribution of the pollen AQPs also reflects a regulatory mechanism that allowing a properly adjusting water and solute exchange.
RESUMO
In darkness, the dicot seedlings produce an apical hook as result of differential cell division and extension at opposite sides of the hypocotyl. This hook protects the apical meristem from mechanical damage during seedling emergence from the soil. In darkness, gibberellins act via the DELLA-PIF (PHYTOCHROME INTERACTING FACTORs) pathway, and ethylene acts via the EIN3/EIL1 (ETHYLENE INSENSITIVE 3/EIN3 like 1)-HLS1 (HOOKLESS 1) pathway to control the asymmetric accumulation of auxin required for apical hook formation and maintenance. These core pathways form a network with multiple points of connection. Light perception by phytochromes and cryptochromes reduces the activity of PIFs and (COP1) CONSTITUTIVE PHOTOMORPHOGENIC 1-both required for hook formation in darkness-, lowers the levels of gibberellins, and triggers hook opening as a component of the switch between heterotrophic and photoautotrophic development. Apical hook opening is thus a suitable model to study the convergence of endogenous and exogenous signals on the control of cell division and cell growth.