Hypocotyl Growth Research Articles

Co-condensation with photoexcited cryptochromes facilitates MAC3A to positively control hypocotyl growth in Arabidopsis.

Cryptochromes (CRYs) are blue light receptors that mediate plant photoresponses through regulating gene expressions. We recently reported that Arabidopsis CRY2 could form light-elicited liquid condensates to control RNA methylation. However, whether CRY2 condensation is involved in other gene expression-regulatory processes remains unclear. Here, we show that MOS4-associated complex subunits 3A and 3B (MAC3A/3B) are CRY-interacting proteins and assembled into nuclear CRY condensates. mac3a3b double mutants exhibit hypersensitive photoinhibition of hypocotyl elongation, suggesting that MAC3A/3B positively control hypocotyl growth. We demonstrate the noncanonical activity of MAC3A as a DNA binding protein that modulates transcription. Genome-wide mapping of MAC3A-binding sites reveals that blue light enhances the association of MAC3A with its DNA targets, which requires CRYs. Further evidence indicates that MAC3A and ELONGATED HYPOCOTYL 5 (HY5) occupy overlapping genomic regions and compete for the same targets. These results argue that photocondensation of CRYs fine-tunes light-responsive hypocotyl growth by balancing the opposed effects of HY5 and MAC3A.

Arabidopsis NF-YC7 Interacts with CRY2 and PIF4/5 to Repress Blue Light-Inhibited Hypocotyl Elongation.

Light is an important environmental factor. Plants adapt to their light environment by developing the optimal phenotypes. Light-mediated hypocotyl growth is an ideal phenotype for studying how plants respond to light. Thus far, many signaling components in light-mediated hypocotyl growth have been reported. Here, we focused on identifying the transcription factors (TFs) involved in blue light-mediated hypocotyl growth. We analyzed the blue-light-mediated hypocotyl lengths of Arabidopsis TF-overexpressing lines and identified three NF-YC proteins, NF-YC7, NF-YC5, and NF-YC8 (NF-YCs being the short name), as the negative regulators in blue light-inhibited hypocotyl elongation. NF-YC-overexpressing lines developed longer hypocotyls than those of the wild type under blue light, while the deficient mutants nf-yc5nf-yc7 and nf-yc7nf-yc8 failed to exhibit hypocotyl elongation under blue light. NF-YCs physically interacted with CRY2 (cryptochrome 2) and PIF4/5 (phytochrome interacting factor 4 or 5), while the NF-YCs-PIF4/5 interactions were repressed by CRY2. Moreover, the overexpression of CRY2 or deficiency of PIF4/5 repressed NF-YC7-induced hypocotyl elongation under blue light. Further investigation revealed that NF-YC7 may increase CRY2 degradation and regulate PIF4/5 activities under blue light. Taken together, this study will provide new insight into the mechanism of how blue light inhibits hypocotyl elongation.

Basally distributed actin array drives embryonic hypocotyl elongation during the seed-to-seedling transition in Arabidopsis.

Seed germination is a vital developmental transition for the production of progeny by sexual reproduction in spermatophytes. The seed-to-seedling transition is predominately driven by hypocotyl cell elongation. However, the mechanism that underlies hypocotyl growth remains largely unknown. In this study, we characterized the actin array reorganization in embryonic hypocotyl epidermal cells. Live-cell imaging revealed a basally organized actin array formed during hypocotyl cell elongation. This polarized actin assembly is a barrel-shaped network, which comprises a backbone of longitudinally aligned actin cables and a fine actin cap linking these cables. We provide genetic evidence that the basal actin array formation requires formin-mediated actin polymerization and directional movement of actin filaments powered by myosin XIs. In fh1-1 and xi3ko mutants, actin filaments failed to reorganize into the basal actin array, and the hypocotyl cell elongation was inhibited compared with wild-type plants. Collectively, our work uncovers the molecular mechanisms for basal actin array assembly and demonstrates the connection between actin polarization and hypocotyl elongation during seed-to-seedling transition.

A Small Compound, HYGIC, Promotes Hypocotyl Growth Through Ectopic Ethylene Response.

Plant seedlings adjust the growth of the hypocotyl in response to surrounding environmental changes. Genetic studies have revealed key players and pathways in hypocotyl growth, such as phytohormones and light signaling. However, because of genetic redundancy in the genome, it is expected that not-yet-revealed mechanisms can be elucidated through approaches different from genetic ones. Here, we identified a small compound, HYGIC (HG), that simultaneously induces hypocotyl elongation and thickening, accompanied by increased nuclear size and enlargement of cortex cells. HG-induced hypocotyl growth required the ethylene signaling pathway activated by endogenous ethylene, involving CONSTITUTIVE PHOTOMORPHOGENIC 1, ETHYLENE INSENSITIVE 2 (EIN2) and redundant transcription factors for ethylene responses, ETHYLENE INSENSITIVE 3 (EIN3) and EIN3 LIKE 1. By using EBS:GUS, a transcriptional reporter of ethylene responses based on an EIN3-binding-cis-element, we found that HG treatment ectopically activates ethylene responses at the epidermis and cortex of the hypocotyl. RNA-seq and subsequent gene ontology analysis revealed that a significant number of HG-induced genes are related to responses to hypoxia. Indeed, submergence, a representative environment where the hypoxia response is induced in nature, promoted ethylene-signaling-dependent hypocotyl elongation and thickening accompanied by ethylene responses at the epidermis and cortex, which resembled the HG treatment. Collectively, the identification and analysis of HG revealed that ectopic responsiveness to ethylene promotes hypocotyl growth, and this mechanism is activated under submergence.

ALLELOPATIC COMPATIBILITY OF COMMON BEAN AND COMPANION CROPS

Purpose. To investigate the allelopathic compatibility of common bean seeds and companion crops, to establish interaction patterns using water extracts from seeds and other plant parts of common bean and companion crops. Methods. Laboratory, statistical. Results. Biotest: interaction of germinating seeds of bean and companion crops in Petri dishes. Biologically active substances from winter and spring triticale seeds (the bean seeds/seeds of companion crops ratio was 1:10) negatively affected bean seedlings, which was seen from all parameters under investigation: hypocotyl length (with the root included), length of the longest adventitious root, the adventitious root number, and true leaf length (with epicotyl included). At a ratio of 1:5, winter triticale-induced inhibition of hypocotyl growth was enhanced up to 38 %, while, on the contrary, spring triticale had a neutral effect on this parameter. A stimulating effect (106 %) of spring triticale seeds on the true bean leaf length (with epicotyl) was noted. For winter and spring triticale in a ratio of 1:1 (compared to the control – without seeds of companion crops), inhibition of the growth of the hypocotyl with the root by 21 % and the true leaf with the epicotyl by 10–9 %, respectively, is observed. Biotest: germination of bean seeds in a water extract from whole seeds of bean and companion crops in Petri dishes. Water extract from spring triticale seeds in a ratio of 1:2 had the greatest stimulating effect on the tap root and the first leaf lengths; winter triticale extract in a ratio of 1:4 had the greatest effect on the adventitious root an epicotyl lengths; bean extract in a ratio of 1:2 had the greatest effect on the epicotyl length. Biotest: germination of bean seeds in a water extract from vegetative mass, roots and post-harvest residues of bean and companion crops in Petri dishes. Water extracts from roots of bean, winter and spring triticale weakly inhibited the main bean root elongation. A neutral allelopathic effect on the bean seed germination was exerted by extract from post-harvest residues of spring triticale. A water extract from top parts of bean had a negative allelopathic effect on germinating bean seeds, indicating self-incompatibility of this crop. Conclusions. The laboratory tests showed that biologically active substances from seeds of both winter triticale and spring triticale at a ratio of 1:10 were toxic for bean ssedlings. Combined germination of bean and spring triticale seeds at a ratio of 1:5 had a more positive effect compared to other ratios of seeds of companion crops, and combined germination of bean seeds with spring and winter triticale seeds at a ratio of 1:1 demonstrated very similar parameters of germinating bean seeds. It was found that water extracts from bean and spring triticale in a ratio of 1:2 and from bean and winter triticale (1:4) had a clear allelopathic effect on the bean parameters. Water extracts from winter triticale (1:1) and spring triticale (1:4) were more toxic to bean seedlings. Water extracts from roots of bean, winter and spring triticale weakly inhibited the main bean root elongation. A water extract from the aboveground parts of bean had a negative allelopathic effect on the germinating seeds of bean, indicating self-incompatibility of this crop. A neutral allelopathic effect on the germination of bean seeds was exerted by extract from post-harvest residues of spring triticale. Combined germination of seeds of bean and companion crops in the laboratory allows for assessments of peculiarities of seed germination and mutual influence of components as early as at the initial stage, for selection of crops for growing in heterogeneous fields aimed at forming a highly productive agrophytocenosis.

Expression Analysis and Interaction Protein Screening of CoZTL in Camellia oleifera Abel

Camellia oleifera Abel., which produces fruits of high comprehensive utilization value, is an important woody oil tree in China. ZEITLUPE (ZTL) is a blue light receptor and clock component protein that is involved in various physiological and biochemical processes. However, the expression pattern and function of C. oleifera ZTL (CoZTL) remain unclear. In this study, the coding sequence of the CoZTL gene was isolated and the protein function was explored using bioinformatics and expression analyses and heterologous expression techniques. The results showed that the CoZTL protein was highly conserved during evolution and was on the same branch of the evolutionary tree as the ZTL proteins from Ipomoea nil and Nicotiana attenuata. CoZTL was mainly expressed in the fruit shells and stems of C. oleifera, and its expression level fluctuated greatly during flower bud development. Transgenic CoZTL-overexpressing Arabidopsis plants showed delayed flowering under long-day conditions as well as light-dependent promotion of hypocotyl elongation. Furthermore, yeast two-hybrid library screening revealed that seven C. oleifera proteins (CoAAT, Coβ-GAL, CoLAT52-like, CoCAR4-like, CoAO, CoUQCC1, and CoADF 2) interacted with CoZTL. Our results indicate that CoZTL plays an important role in C. oleifera flowering and hypocotyl growth.

Temperature regulation of auxin-related gene expression and its implications for plant growth.

Twenty-five years ago, a seminal paper demonstrated that warm temperatures increase auxin levels to promote hypocotyl growth in Arabidopsis thaliana. Here we highlight recent advances in auxin-mediated thermomorphogenesis and identify unanswered questions. In the warmth, PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PIF7 bind the YUCCA8 gene promoter and, in concert with histone modifications, enhance its expression to increase auxin synthesis in the cotyledons. Once transported to the hypocotyl, auxin promotes cell elongation. The meta-analysis of expression of auxin-related genes in seedlings exposed to temperatures ranging from cold to hot shows complex patterns of response. Changes in auxin only partially account for these responses. The expression of many SMALL AUXIN UP RNA (SAUR) genes reaches a maximum in the warmth, decreasing towards both temperature extremes in correlation with the rate of hypocotyl growth. Warm temperatures enhance primary root growth, the response requires auxin, and the hormone levels increase in the root tip but the impacts on cell division and cell expansion are not clear. A deeper understanding of auxin-mediated temperature control of plant architecture is necessary to face the challenge of global warming.

Constituent content and allelopathic potential of eighteen extracts for the control of Urochloa decumbens under laboratory conditions

Invasive grasses, those of the genus Urochloa act aggressively, thereby inhibiting the germination and growth of native species. We investigated the allelopathic potential and constituent content of different plant species to determine their effect on the germination of Urochloa decumbens (Stapf) R.D. Webster. Eighteen (18) species from the families Anacardiaceae (1), Annonaceae (6), Euphorbiaceae (1), Fabaceae (2), Myrtaceae (1), Rubiaceae (4), Sapindaceae (2), and Tropaeolaceae (1) were selected to obtain methanolic extracts at 1% (m/v). The total phenols, flavonoids, condensed tannins, flavonols, and saponins were evaluated by colorimetric methods. To evaluate the allelopathic effect of methanolic extracts 25 seeds from U. decumbens were distributed in Petri dishes containing two sheets of germitest paper and 2 mL of extract, and they were maintained at 25 °C under white light. All methanolic extracts showed total phenols, flavonoids, flavonols, and condensed tannins; however, saponin was identified in A. coriacea, A. crassiflora, A. sylvatica, Psychotria carthagenensis, P. leiocarpa, and Tropaeolum majus. Annona dioica (Annonaceae), Stryphnodendron adstringens (Fabaceae), and Palicourea crocea (Rubiaceae) have allelopathic potential and showed decelerated U. decumbens seed germination and inhibited hypocotyl and radicle growth. These findings provide insights into alternative methods for controlling U. decumbens in areas of ecological restoration.

MYB112 connects light and circadian clock signals to promote hypocotyl elongation in Arabidopsis.

Ambient light and the endogenous circadian clock play key roles in regulating Arabidopsis (Arabidopsis thaliana) seedling photomorphogenesis. PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) acts downstream of both light and the circadian clock to promote hypocotyl elongation. Several members of the R2R3-MYB transcription factor (TF) family, the most common type of MYB TF family in Arabidopsis, have been shown to be involved in regulating photomorphogenesis. Nonetheless, whether R2R3-MYB TFs are involved in connecting the light and clock signaling pathways during seedling photomorphogenesis remains unknown. Here, we report that MYB112, a member of the R2R3-MYB family, acts as a negative regulator of seedling photomorphogenesis in Arabidopsis. The light signal promotes the transcription and protein accumulation of MYB112. myb112 mutants exhibit short hypocotyls in both constant light and diurnal cycles. MYB112 physically interacts with PIF4 to enhance the transcription of PIF4 target genes involved in the auxin pathway, including YUCCA8 (YUC8), INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19), and IAA29. Furthermore, MYB112 directly binds to the promoter of LUX ARRHYTHMO (LUX), the central component of clock oscillators, to repress its expression mainly in the afternoon and relieve LUX-inhibited expression of PIF4. Genetic evidence confirms that LUX acts downstream of MYB112 in regulating hypocotyl elongation. Thus, the enhanced transcript accumulation and transcriptional activation activity of PIF4 by MYB112 additively promotes the expression of auxin-related genes, thereby increasing auxin synthesis and signaling and fine-tuning hypocotyl growth under diurnal cycles.

HSP90 in morphogenesis: taking the heat and keeping the dark.

This article is a Commentary on Zeng et al. (2023), 239: 1253–1265.

Heavy metals tolerance on seed germination and growth of serpentine plant species Alyssum murale L.

Alyssum murale L. is a nickel hyperaccumulator herbaceous perennial species in a natural serpentine soil and adapted to arid, infertile soils. The objective of this study was to investigate how the seed germination, root, and hypocotyl growth of this plant species respond to exposure to different concentrations of heavy metals such as lead (Pb), cadmium (Cd), nickel (Ni), chromium (Cr) and manganese (Mn). The highest germination, even higher than in the control group, was observed at lower concentrations of Ni, Cd, Pb and Mn, while almost all higher concentrations of the metals decreased germination. Germination time was significantly slower (from about 6 to 10 days) for seeds treated with higher metal concentrations, especially Mn, Cd and Ni, and faster (from about 3 to 5 days) for seeds treated with lower concentrations. The strongest inhibitory effect on root and hypocotyl length occurred in treatments with different concentrations of Pb, Cd, and Mn, and seeds treated with lower concentrations of Ni showed a positive effect on root and hypocotyl growth. Seeds treated with Ni showed relatively high tolerance to this metal, presenting the potential for practical use in various fields of phytoremediation technology.

Phytochrome-interacting factor PIF3 integrates phytochrome B and UVB signaling pathways to regulate gibberellin- and auxin-dependent growth in cucumber hypocotyls.

In Arabidopsis, the photoreceptors phytochrome B- (PhyB) and UVB resistance 8- (UVR8) mediated light responses play a major role in regulating photomorphogenic hypocotyl growth, but how they crosstalk to coordinate this process is not well understood. Here we report map-based cloning and functional characterization of a UVB-insensitive, long-hypocotyl mutant, lh1, and a wild-type-like lh2 mutant in cucumber, Cucumis sativus, which encodes a defective CsPhyB and a key gibberellic acid (GA) biosynthesis enzyme CsGA20ox-2, respectively. The lh2 mutation was epistatic to lh1 and partly suppressed long-hypocotyl phenotype in the lhl1lh2 double mutant. We identified phytochrome interacting factor (PIF) CsPIF3 that played a critical role in integrating the red/far-red and UVB light responses for hypocotyl growth. We show that two modules, CsPhyB-CsPIF3-CsGA20ox-2 (GA oxidase2)-DELLA and CsPIF3-CsARF18 (auxin response factor 18) mediate CsPhyB-regulated hypocotyl elongation through GA and auxin pathways, respectively, in which CsPIF3 binds to the G-/E-box motifs in the promoters of CsGA20ox-2 and CsARF18 to regulate their expression. We also identified a new physical interaction between CsPIF3 and CsUVR8 mediating CsPhyB-dependent, UVB-induced hypocotyl growth inhibition. Our work suggests that hypocotyl growth in cucumber involves a complex interplay of multiple photoreceptor- and phytohormone-mediated signaling pathways that show both conservation with and divergence from those in Arabidopsis.

WAVE-DAMPENED2-LIKE4 modulates the hyper-elongation of light-grown hypocotyl cells.

Light, temperature, water, and nutrient availability influence how plants grow to maximize access to resources. Axial growth, the linear extension of tissues by coordinated axial cell expansion, plays a central role in these adaptive morphological responses. Using Arabidopsis (Arabidopsis thaliana) hypocotyl cells to explore axial growth control mechanisms, we investigated WAVE-DAMPENED2-LIKE4 (WDL4), an auxin-induced, microtubule-associated protein and member of the larger WDL gene family shown to modulate hypocotyl growth under changing environmental conditions. Loss-of-function wdl4 seedlings exhibited a hyper-elongation phenotype under light conditions, continuing to elongate when wild type Col-0 hypocotyls arrested and reaching 150-200% of wild type length before shoot emergence. wdl4 seedling hypocotyls showed dramatic hyper-elongation (500%) in response to temperature elevation, indicating an important role in morphological adaptation to environmental cues. WDL4 associated with microtubules under both light and dark growth conditions, and no evidence was found for altered microtubule array patterning in loss-of-function wdl4 mutants under various conditions. Examination of hormone responses showed altered sensitivity to ethylene and evidence for changes in the spatial distribution of the auxin-dependent DR5:GFP reporter. Our data provide evidence that WDL4 regulates hypocotyl cell elongation without substantial changes to microtubule array patterning, suggesting an unconventional role in axial growth control.

A 5.5-kb LTR-retrotransposon insertion inside phytochrome B gene (CsPHYB) results in long hypocotyl and early flowering in cucumber (Cucumis sativus L.)

The novel spontaneous long hypocotyl and early flowering (lhef) mutation in cucumber is due to a 5551-bp LTR-retrotransposon insertion in CsPHYB gene encoding PHYTOCHROME B, which plays a major role in regulating photomorphogenic hypocotyl growth and flowering. Hypocotyl length and flowering time are important for establishing high-quality seedlings in modern cucumber production, but little is known for the underlying molecular mechanisms of these two traits. In this study, a spontaneous cucumber long hypocotyl and early flowering mutant was identified and characterized. Based on multiple lines of evidence, we show that cucumber phytochrome B (CsPHYB) is the candidate gene for this mutation, and a 5551-bp LTR-retrotransposon insertion in the first exon of CsPHYB was responsible for the mutant phenotypes. Uniqueness of the mutant allele at CsPHYB was verified in 114 natural cucumber lines. Ectopic expression of the CsPHYB in Arabidopsis phyB mutant rescued the long hypocotyl and early flowering phenotype of phyB-9 mutant. The wild-type CsPHYB protein was localized on the membrane and cytoplasm under white light condition, whereas in the nucleus under red light, it is consistent with its roles as a red-light photoreceptor in Arabidopsis. However, the mutant csphyb protein was localized on the membrane and cytoplasm under both white and red-light conditions. Expression dynamics of CsPHYB and several cell elongation-related genes were positively correlated with hypocotyl elongation; the transcription levels of key positive and negative regulators for flowering time were also consistent with the anthesis dates in the mutant and wild-type plants. Yeast two hybrid and bimolecular fluorescence complementation assays identified physical interactions between CsPHYB and phytochrome interacting factor 3/4 (CsPIF3/4). These findings will provide new insights into the roles of the CsPHYB in cucumber hypocotyl growth and flowering time.

A conserved brassinosteroid-mediated BES1-CERP-EXPA3 signaling cascade controls plant cell elongation

Continuous plant growth is achieved by cell division and cell elongation. Brassinosteroids control cell elongation and differentiation throughout plant life. However, signaling cascades underlying BR-mediated cell elongation are unknown. In this study, we introduce cotton fiber, one of the most representative single-celled tissues, to decipher cell-specific BR signaling. We find that gain of function of GhBES1, a key transcriptional activator in BR signaling, enhances fiber elongation. The chromatin immunoprecipitation sequencing analysis identifies a cell-elongation-related protein, GhCERP, whose transcription is directly activated by GhBES1. GhCERP, a downstream target of GhBES1, transmits the GhBES1-mediated BR signaling to its target gene, GhEXPA3-1. Ultimately, GhEXPA3-1 promotes fiber cell elongation. In addition, inter-species functional analysis of the BR-mediated BES1-CERP-EXPA3 signaling cascade also promotes Arabidopsis root and hypocotyl growth. We propose that the BES1-CERP-EXPA3 module may be a broad-spectrum pathway that is universally exploited by diverse plant species to regulate BR-promoted cell elongation.

MicroRNA156 conditions auxin sensitivity to enable growth plasticity in response to environmental changes in Arabidopsis

MicroRNAs (miRNAs) play diverse roles in plant development, but whether and how miRNAs participate in thermomorphogenesis remain ambiguous. Here we show that HYPONASTIC LEAVES 1 (HYL1)—a key component of miRNA biogenesis—acts downstream of the thermal regulator PHYTOCHROME INTERACTING FACTOR 4 in the temperature-dependent plasticity of hypocotyl growth in Arabidopsis. A hyl1-2 suppressor screen identified a dominant dicer-like1 allele that rescues hyl1-2’s defects in miRNA biogenesis and thermoresponsive hypocotyl elongation. Genome-wide miRNA and transcriptome analysis revealed microRNA156 (miR156) and its target SQUAMOSA PROMOTER-BINDING-PROTEIN-LIKE 9 (SPL9) to be critical regulators of thermomorphogenesis. Surprisingly, perturbation of the miR156/SPL9 module disengages seedling responsiveness to warm temperatures by impeding auxin sensitivity. Moreover, miR156-dependent auxin sensitivity also operates in the shade avoidance response at lower temperatures. Thus, these results unveil the miR156/SPL9 module as a previously uncharacterized genetic circuit that enables plant growth plasticity in response to environmental temperature and light changes.

Cis-Golgi phosphate transporters harboring an EXS domain are essential for plant growth and development.

Cell wall synthesis and protein glycosylation require the import of nucleotide diphosphate-sugar conjugates into the Golgi that must be counterbalanced by phosphate (Pi) export. Numerous Golgi nucleotide-sugar transporters have been characterized, but transporters mediating Golgi Pi export remain poorly understood. We used plant and yeast genetics to characterize the role of 2 Arabidopsis (Arabidopsis thaliana) proteins possessing an EXS domain, namely ERD1A and ERD1B, in Golgi Pi homeostasis. ERD1A and ERD1B localized in cis-Golgi and were broadly expressed in vegetative and reproductive tissues. We identified ERD1 putative orthologs in algae, bryophytes, and vascular plants. Expressing ERD1A and ERD1B in yeast complemented the erd1 mutant phenotype of cellular Pi loss via exocytosis associated with reduced Golgi Pi export. The Arabidopsis erd1a mutant had a similar phenotype of apoplastic Pi loss dependent on exocytosis. ERD1A overexpression in Nicotiana benthamiana and Arabidopsis led to partial mislocalization of ERD1A to the plasma membrane and specific Pi export to the apoplastic space. Arabidopsis erd1a had defects in cell wall biosynthesis, which were associated with reduced shoot development, hypocotyl growth, cell wall extensibility, root elongation, pollen germination, pollen tube elongation, and fertility. We identified ERD1 proteins as Golgi Pi exporters that are essential for optimal plant growth and fertility.

Exogenous 6-BA inhibited hypocotyl elongation under darkness in Picea crassifolia Kom revealed by transcriptome profiling.

Hypocotyl elongation is an important process in plant growth and development, and is under hormonal regulatory signaling pathways. In our study, exogenous 6-BA significantly inhibited Picea crassifolia hypocotyl elongation more than ethylene in the dark, indicating the existence of different regulatory strategies in conifers, therefore, the P. crassifolia transcriptome was studied to explore the responsive genes and their regulatory pathways for exogenous N6-benzyladenine (6-BA) inhibition of hypocotyl elongation using RNA-Sequencing approach. We present the first transcriptome assembly of P. crassifolia obtained from 24.38 Gb clean data. With lowly-expressed and short contigs excluded, the assembly contains roughly 130,612 unigenes with an N50 length of 1,278 bp. Differential expression analysis found 3,629 differentially expressed genes (DEGs) and found that the differential expression fold of genes was mainly concentrated between 2 and 8 (1 ≤ log2FoldChange ≤ 3). Functional annotation showed that the GO term with the highest number of enriched genes (83 unigenes) was the shoot system development (GO: 0048367) and the KEGG category, plant hormone signal transduction (ko04075), was enriched 30 unigenes. Further analysis revealed that several cytokinin dehydrogenase genes (PcCTD1, PcCTD3 and PcCTD6) catabolized cytokinins, while xyloglucan endotransglucosylase hydrolase gene (PcXTH31), WALLS ARE THIN 1-like gene (PcWAT1-1) and Small auxin-induced gene (PcSAUR15) were strongly repressed thus synergistically completing the inhibition of hypocotyl elongation in P. crassifolia. Besides, PcbHLH149, PcMYB44 and PcERF14 were predicted to be potential core TFs that may form a multi-layered regulatory network with the above proteins for the regulation of hypocotyl growth.

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.

Evaluation of Abnormal Hypocotyl Growth of Mutant Capsicum annuum Plants

Horticulture is a dynamically evolving and an ever-changing sector which needs new ideas, plant materials, and cultivating methods to produce more. Involving different mutants in breeding lines may lead to new opportunities to create new cultivating methods. pcx (procumbent plant) and tti (tortuosa internodi) Capsicum annuum mutant plants, which present abnormal stem growth, were investigated in various in vitro experiments. The pcx breeding line presents highly diverse hypocotyl growth even in the early phenophase, such as normally growing plants and the ‘laying’ habit. On the other hand, tti plants only present their elongated slender stem trait in a more mature phase. In our experiment of reorientation, we used one-sided illumination, where each of the phenotypes sensed and reacted to light, and only the pcx plants exhibited a negative gravitropic response. It was also the result that the tti plants sensed gravity, but the weak structure of the hypocotyls made them incapable of following its direction. Since the pcx plants were the only ones with an ‘antigravitropic’ growth, we used them to evaluate the time course they needed to adapt and follow the gravity vector after reorientation. The pcx plants sensing gravity adapted similarly to controls and started bending after 120 min, but those which presented as ‘anti-gravitropic’ did not respond even after 420 min.