Brassinosteroids Are Master Regulators of Gibberellin Biosynthesis in Arabidopsis

A multifaceted crosstalk between brassinosteroid and gibberellin regulates the resistance of cucumber to Phytophthora melonis

Cucumber plants are highly susceptible to the hemibiotroph oomycete Phytophthora melonis. However, the mechanism of resistance to cucumber blight remains poorly understood. Here, we demonstrated that cucumber plants with impairment in the biosynthesis of brassinosteroids (BRs) or gibberellins (GAs) were more susceptible to P. melonis. By contrast, increasing levels of endogenous BRs or exogenously application of 24-epibrassinolide enhanced the resistance of cucumber plants against P. melonis. Furthermore, we found that both knockout and overexpression of the BR biosynthesis gene CYP85A1 reduced the endogenous GA3 content compared with that of wild-type plants under the condition of inoculation with P. melonis, and the enhancement of disease resistance conferred by BR was inhibited in plants with silencing of the GA biosynthetic gene GA20ox1 or KAO. Together, these findings suggest that GA homeostasis is an essential factor mediating BRs-induced disease resistance. Moreover, BZR6, a key regulator of BR signaling, was found to physically interact with GA20ox1, thereby suppressing its transcription. Silencing of BZR6 promoted endogenous GA biosynthesis and compromised GA-mediated resistance. These findings reveal multifaceted crosstalk between BR and GA in response to pathogen infection, which can provide a new approach for genetically controlling P. melonis damage in cucumber production.

Brassinosteroid regulates stomatal development in etiolated Arabidopsis cotyledons via transcription factors BZR1 and BES1

Brassinosteroids (BRs) are phytohormones that regulate stomatal development. In this study, we report that BR represses stomatal development in etiolated Arabidopsis (Arabidopsis thaliana) cotyledons via transcription factors BRASSINAZOLE RESISTANT 1 (BZR1) and bri1-EMS SUPPRESSOR1 (BES1), which directly target MITOGEN-ACTIVATED PROTEIN KINASE KINASE 9 (MKK9) and FAMA, 2 important genes for stomatal development. BZR1/BES1 bind MKK9 and FAMA promoters in vitro and in vivo, and mutation of the BZR1/BES1 binding motif in MKK9/FAMA promoters abolishes their transcription regulation by BZR1/BES1 in plants. Expression of a constitutively active MKK9 (MKK9DD) suppressed overproduction of stomata induced by BR deficiency, while expression of a constitutively inactive MKK9 (MKK9KR) induced high-density stomata in bzr1-1D. In addition, bzr-h, a sextuple mutant of the BZR1 family of proteins, produced overabundant stomata, and the dominant bzr1-1D and bes1-D mutants effectively suppressed the stomata-overproducing phenotype of brassinosteroid insensitive 1-116 (bri1-116) and brassinosteroid insensitive 2-1 (bin2-1). In conclusion, our results revealed important roles of BZR1/BES1 in stomatal development, and their transcriptional regulation of MKK9 and FAMA expression may contribute to BR-regulated stomatal development in etiolated Arabidopsis cotyledons.

OsWRKY78 regulates panicle exsertion via gibberellin signaling pathway in rice

Panicle exsertion is one of the crucial agronomic traits in rice (Oryza sativa). Shortening of panicle exsertion often leads to panicle enclosure and severely reduces seed production. Gibberellin (GA) plays important roles in regulating panicle exsertion. However, the underlying mechanism and the relative regulatory network remain elusive. Here, we characterized the oswrky78 mutant showing severe panicle enclosure, and found that the defect of oswrky78 is caused by decreased bioactive GA contents. Biochemical analysis demonstrates that OsWRKY78 can directly activate GA biosynthesis and indirectly suppress GA metabolism. Moreover, we found OsWRKY78 can interact with and be phosphorylated by mitogen-activated protein kinase (MAPK) kinase OsMAPK6, and this phosphorylation can enhance OsWRKY78 stability and is necessary for its biological function. Taken together, these results not only reveal the critical function of OsWRKY78, but also reveal its mechanism via mediating crosstalk between MAPK and the GA signaling pathway in regulating panicle exsertion.

Transcription factors BZR2/MYC2 modulate brassinosteroid and jasmonic acid crosstalk during pear dormancy

Bud dormancy is an important physiological process during winter. Its release requires a certain period of chilling. In pear (Pyrus pyrifolia), the abscisic acid (ABA)-induced expression of DORMANCY-ASSOCIATED MADS-box (DAM) genes represses bud break, whereas exogenous gibberellin (GA) promotes dormancy release. However, with the exception of ABA and GA, the regulatory effects of phytohormones on dormancy remain largely uncharacterized. In this study, we confirmed brassinosteroids (BRs) and jasmonic acid (JA) contribute to pear bud dormancy release. If chilling accumulation is insufficient, both 24-epibrassinolide (EBR) and methyl jasmonic acid (MeJA) can promote pear bud break, implying that they positively regulate dormancy release. BRASSINAZOLE RESISTANT 2 (BZR2), which is a BR-responsive transcription factor, inhibited PpyDAM3 expression and accelerated pear bud break. The transient overexpression of PpyBZR2 increased endogenous GA, JA, and JA-Ile levels. In addition, the direct interaction between PpyBZR2 and MYELOCYTOMATOSIS 2 (PpyMYC2) enhanced the PpyMYC2-mediated activation of Gibberellin 20-oxidase genes PpyGA20OX1L1 and PpyGA20OX2L2 transcription, thereby increasing GA3 contents and accelerating pear bud dormancy release. Interestingly, treatment with 5 μm MeJA increased the bud break rate, while also enhancing PpyMYC2-activated PpyGA20OX expression and increasing GA3,4 contents. The 100 μm MeJA treatment decreased the PpyMYC2-mediated activation of the PpyGA20OX1L1 and PpyGA20OX2L2 promoters and suppressed the inhibitory effect of PpyBZR2 on PpyDAM3 transcription, ultimately inhibiting pear bud break. In summary, our data provide insights into the crosstalk between the BR and JA signaling pathways that regulate the BZR2/MYC2-mediated pathway in the pear dormancy release process.

OsCSN2 orchestrates Oryza sativa L. growth and development through modulation of the GA and BR pathways

The COP9 signalosome (CSN) is a conserved protein complex found in higher eukaryotes, consisting of eight subunits, and it plays a crucial role in regulating various processes of plant growth and development. Among these subunits, CSN2 is one of the most conserved components within the COP9 signalosome complex. Despite its prior identification in other species, its specific function in Oryza sativa L. (Rice) has remained poorly understood. In this study, we investigated the role of CSN2 in rice using gene editing CRISPR/Cas9 technology and overexpression techniques. We created two types of mutants: the oscsn2 mutant and the OsCSN2-OE mutant, both in the background of rice, and also generated point mutants of OsCSN2 (OsCSN2K64E, OsCSN2K67E, OsCSN2K71E and OsCSN2K104E) to further explore the regulatory function of OsCSN2. Phenotypic observation and gene expression analysis were conducted on plants from the generated mutants, tracking their growth from the seedling to the heading stages. The results showed that the loss and modification of OsCSN2 had limited effects on plant growth and development during the early stages of both the wild-type and mutant plants. However, as the plants grew to 60 days, significant differences emerged. The OsCSN2 point mutants exhibited increased tillering compared to the OsCSN2-OE mutant plants, which were already at the tillering stage. On the other hand, the OsCSN2 point mutant had already progressed to the heading and flowering stages, with the shorter plants. These results, along with functional predictions of the OsCSN2 protein, indicated that changes in the 64th, 67th, 71st, and 104th amino acids of OsCSN2 affected its ubiquitination site, influencing the ubiquitination function of CSN and consequently impacting the degradation of the DELLA protein SLR1. Taken together, it can be speculated that OsCSN2 plays a key role in GA and BR pathways by influencing the functional regulation of the transcription factor SLR1 in CSN, thereby affecting the growth and development of rice and the number of tillers.

Leaf growth - complex regulation of a seemingly simple process

Understanding the underlying mechanisms of plant development is crucial to successfully steer or manipulate plant growth in a targeted manner. Leaves, the primary sites of photosynthesis, are vital organs for many plant species, and leaf growth is controlled by a tight temporal and spatial regulatory network. In this review, we focus on the genetic networks governing leaf cell proliferation, one major contributor to final leaf size. First, we provide an overview of six regulator families of leaf growth in Arabidopsis: DA1, PEAPODs, KLU, GRFs, the SWI/SNF complexes, and DELLAs, together with their surrounding genetic networks. Next, we discuss their evolutionary conservation to highlight similarities and differences among species, because knowledge transfer between species remains a big challenge. Finally, we focus on the increase in knowledge of the interconnectedness between these genetic pathways, the function of the cell cycle machinery as their central convergence point, and other internal and environmental cues.

Dynamic Phytomeric Growth Contributes to Local Adaptation in Barley

Vascular plants have segmented body axes with iterative nodes and internodes. Appropriate node initiation and internode elongation are fundamental to plant fitness and crop yield; however, how these events are spatiotemporally coordinated remains elusive. We show that in barley (Hordeum vulgare L.), selections during domestication have extended the apical meristematic phase to promote node initiation, but constrained subsequent internode elongation. In both vegetative and reproductive phases, internode elongation displays a dynamic proximal-distal gradient, and among subpopulations of domesticated barleys worldwide, node initiation and proximal internode elongation are associated with latitudinal and longitudinal gradients, respectively. Genetic and functional analyses suggest that, in addition to their converging roles in node initiation, flowering-time genes have been repurposed to specify the timing and duration of internode elongation. Our study provides an integrated view of barley node initiation and internode elongation and suggests that plant architecture should be recognized as a collection of dynamic phytomeric units in the context of crop adaptive evolution.

Identification and Characterization of the BZR Transcription Factor Genes Family in Potato (Solanum tuberosum L.) and Their Expression Profiles in Response to Abiotic Stresses

Brassinazole resistant (BZR) genes act downstream of the brassinosteroid signaling pathway regulating plant growth and development and participating in plant stress responses. However, the BZR gene family has not systematically been characterized in potato. We identified eight BZR genes in Solanum tuberosum, which were distributed among seven chromosomes unequally and were classified into three subgroups. Potato and tomato BZR proteins were shown to be closely related with high levels of similarity. The BZR gene family members in each subgroup contained similar conserved motifs. StBZR genes exhibited tissue-specific expression patterns, suggesting their functional differentiation during evolution. StBZR4, StBZR7, and StBZR8 were highly expressed under white light in microtubers. StBZR1 showed a progressive up-regulation from 0 to 6 h and a progressive down-regulation from 6 to 24 h after drought and salt stress. StBZR1, StBZR2, StBZR4, StBZR5, StBZR6, StBZR7 and StBZR8 were significantly induced from 0 to 3 h under BR treatment. This implied StBZR genes are involved in phytohormone and stress response signaling pathways. Our results provide a theoretical basis for understanding the functional mechanisms of BZR genes in potato.

Construction and analysis of the tapping panel dryness-related lncRNA/circRNA-miRNA-mRNA ceRNA network in latex of Hevea brasiliensis

Tapping panel dryness (TPD) results in a severe reduction in latex yield in Hevea brasiliensis. However, the molecular regulatory mechanisms of TPD occurrence are still largely unclear. In this study, whole-transcriptome sequencing was carried out on latex from TPD and healthy trees. In total, 7078 long noncoding RNAs (lncRNAs), 3077 circular RNAs (circRNAs), 4956 miRNAs, and 25041 mRNAs were identified in latex, among which 435 lncRNAs, 68 circRNAs, 320 miRNAs, and 1574 mRNAs were differentially expressed in the latex of TPD trees. GO and KEGG analyses indicated that plant hormone signal transduction, MAPK signaling pathway, and ubiquitin-mediated proteolysis were the key pathways associated with TPD onset. Phytohormone profiling revealed significant changes in the contents of 28 hormonal compounds, among which ACC, ABA, IAA, GA, and JA contents were increased, while SA content was reduced in TPD latex, suggesting that hormone homeostasis is disrupted in TPD trees. Furthermore, we constructed a TPD-related competitive endogenous RNA (ceRNA) regulatory network of lncRNA/circRNA-miRNA-mRNA with 561 edges and 434 nodes (188 lncRNAs, 5 circRNAs, 191 miRNAs, and 50 mRNAs) and identified two hub lncRNAs (MSTRG.11908.1 and MSTRG.8791.1) and four hub miRNAs (hbr-miR156, miR156-x, miRf10477-y, and novel-m0452-3p). Notably, the lncRNA-miR156/157-SPL module containing three hubs probably plays a crucial role in TPD onset. The expression of network hubs and the lncRNA-miR156/157-SPL module were further validated by qRT-PCR. Our results reveal the TPD-associated ceRNA regulatory network of lncRNA/circRNA-miRNA-mRNA in latex and lay a foundation for further investigation of molecular regulatory mechanisms for TPD onset in H. brasiliensis.

TaBZR1 enhances wheat salt tolerance via promoting ABA biosynthesis and ROS scavenging

Brassinosteroids (BRs) are vital plant steroid hormones involved in numerous aspects of plant life including growth, development, and responses to various stresses. However, the underlying mechanisms of how BR regulates abiotic stress responses in wheat (Triticum aestivum L.) remain to be elucidated. Here, we find that BR signal core transcription factor BRASSINAZOLE-RESISTANT1 (TaBZR1) is significantly up-regulated by salt treatment. Overexpression of Tabzr1-1D (a gain-of-function TaBZR1 mutant protein) improves wheat salt tolerance. Furthermore, we show that TaBZR1 binds directly to the G-box motif in the promoter of ABA biosynthesis gene TaNCED3 to activate its expression and promotes ABA accumulation. Moreover, TaBZR1 associates with the promoters of ROS-scavenging genes TaGPX2 and TaGPX3 to activate their expression. Taken together, our results elucidate that TaBZR1 improves salt-stress tolerance by activating some genes involved in the biosynthesis of ABA and ROS scavenging in wheat, which gives us a new strategy to improve the salt tolerance of wheat.

Important Factors Controlling Gibberellin Homeostasis in Plant Height Regulation

Plant height is an important agronomic trait that is closely associated with crop yield and quality. Gibberellins (GAs), a class of highly efficient plant growth regulators, play key roles in regulating plant height. Increasing reports indicate that transcriptional regulation is a major point of regulation of the GA pathways. Although substantial knowledge has been gained regarding GA biosynthetic and signaling pathways, important factors contributing to the regulatory mechanisms homeostatically controlling GA levels remain to be elucidated. Here, we provide an overview of current knowledge regarding the regulatory network involving transcription factors, noncoding RNAs, and histone modifications involved in GA pathways. We also discuss the mechanisms of interaction between GAs and other hormones in plant height development. Finally, future directions for applying knowledge of the GA hormone in crop breeding are described.

A Plate Growth Assay to Quantify Embryonic Root Development of Zea mays

Murashige-Skoog medium solutions have been used in a variety of plant plate growth assays, yet most research uses Arabidopsis thaliana as the study organism. For larger seeds such as maize (Zea mays), most protocols employ a paper towel roll method for experiments, which often involves wrapping maize seedlings in wet, sterile germination paper. What the paper towel roll method lacks, however, is the ability to image the roots over time without risk of contamination. Here, we describe a sterile plate growth assay that contains Murashige-Skoog medium to grow seedlings starting two days after germination. This protocol uses a section of a paper towel roll method to achieve uniform germination of maize seedlings, which are sterilely transferred onto large acrylic plates for the duration of the experiment. The media can undergo modification to include an assortment of plant hormones, exogenous sugars, and other chemicals. The acrylic plates allow researchers to freely image the plate without disturbing the seedlings and control the environment in which the seedlings are grown, such as modifications in temperature and light. Additionally, the protocol is widely adaptable for use with other cereal crops. Key features • Builds upon plate growth methods routinely used for Arabidopsis seedlings but that are inadequate for maize. • Real-time photographic analysis of seedlings up to two weeks following germination. • Allows for testing of various growth conditions involving an assortment of additives and/or modification of environmental conditions. • Samples are able to be collected for genotype screening.

Influence of Exogenous 24-Epicasterone on the Hormonal Status of Soybean Plants

Brassinosteroids (BRs) are key phytohormones involved in the regulation of major processes of cell metabolism that guide plant growth. In the past decades, new evidence has made it clear that BRs also play a key role in the orchestration of plant responses to many abiotic and biotic stresses. In the present work, we analyzed the impact of foliar treatment with 24-epicastasterone (ECS) on the endogenous content of major phytohormones (auxins, salicylic acid, jasmonic acid, and abscisic acid) and their intermediates in soybean leaves 7 days following the treatment. Changes in the endogenous content of phytohormones have been identified and quantified by LC/MS. The obtained results point to a clear role of ECS in the upregulation of auxin content (indole-3-acetic acid, IAA) and downregulation of salicylic, jasmonic, and abscisic acid levels. These data confirm that under optimal conditions, ECS in tested concentrations of 0.25 µM and 1 µM might promote growth in soybeans by inducing auxin contents. Benzoic acid (a precursor of salicylic acid (SA)), but not SA itself, has also been highly accumulated under ECS treatment, which indicates an activation of the adaptation strategies of cell metabolism to possible environmental challenges.

Light signaling as cellular integrator of multiple environmental cues in plants

Plants being sessile need to rapidly adapt to the constantly changing environment through modifications in their internal clock, metabolism, and gene expression. They have evolved an intricate system to perceive and transfer the signals from the primary environmental factors namely light, temperature and water to regulate their growth development and survival. Over past few decades rigorous research using molecular genetics approaches, especially in model plant Arabidopsis, has resulted in substantial progress in discovering various photoreceptor systems and light signaling components. In parallel several molecular pathways operating in response to other environmental cues have also been elucidated. Interestingly, the studies have shown that expression profiles of genes involved in photomorphogenesis can undergo modulation in response to other cues from the environment. Recently, the photoreceptor, PHYB, has been shown to function as a thermosensor. Downstream components of light signaling pathway like COP1 and PIF have also emerged as integrating hubs for various kinds of signals. All these findings indicate that light signaling components may act as central integrator of various environmental cues to regulate plant growth and development processes. In this review, we present a perspective on cross talk of signaling mechanisms induced in response to myriad array of signals and their integration with the light signaling components. By putting light signals on the central stage, we propose the possibilities of enhancing plant resilience to the changing environment by fine-tuning the genetic manipulation of its signaling components in the future.

Plant-specific BLISTER interacts with kinase BIN2 and BRASSINAZOLE RESISTANT1 during skotomorphogenesis

Brassinosteroids play an essential role in promoting skotomorphogenesis, yet the underlying mechanisms remain unknown. Here we report that a plant-specific BLISTER (BLI) protein functions as a positive regulator of both BR signaling and skotomorphogenesis in Arabidopsis (Arabidopsis thaliana). We found that the glycogen synthase kinase 3 (GSK3)-like kinase BRASSINOSTEROID INSENSITIVE2 interacts with and phosphorylates BLI at 4 phosphorylation sites (Ser70, Ser146, Thr256, and Ser267) for degradation; in turn, BR inhibits degradation of BLI. Specifically, BLI cooperates with the BRASSINAZOLE RESISTANT1 (BZR1) transcription factor to facilitate the transcriptional activation of BR-responsive genes. Genetic analyses indicated that BLI is essentially required for BZR1-mediated hypocotyl elongation in the dark. Intriguingly, we reveal that BLI and BZR1 orchestrate the transcriptional expression of gibberellin (GA) biosynthetic genes to promote the production of bioactive GAs. Our results demonstrate that BLI acts as an essential regulator of Arabidopsis skotomorphogenesis by promoting BR signaling and GA biosynthesis.

The Maize ZmBES1/BZR1-9 Transcription Factor Accelerates Flowering in Transgenic Arabidopsis and Rice

In model plants, the BRI1-EMS suppressor 1 (BES1)/brassinazole-resistant 1 (BZR1) transcription factors play vital roles in regulating growth, development, and stimuli response. However, the roles of maize ZmBES1/BZR1 members are largely unknown. In this research, the ZmBES1/BZR1-9 gene was ectopically expressed in Arabidopsis and rice for the phenotyping of flowering. We found that the complementation and overexpression of ZmBES1/BZR1-9 in bes1-D mutant and wild type Arabidopsis both resulted in early flowering that was about 10 days shorter than in the untransformed control under long-day conditions. In addition, there was no difference in the rosette leaf number between all transgenic lines and the control. Subsequently, the ZmBES1/BZR1-9 gene was overexpressed in rice. It was found that overexpression lines of rice exhibited early flowering with heading dates that were 8 days shorter compared with untransformed plants. Moreover, the results of RNA-seq and qRT-PCR showed that five flowering-regulated genes, namely At2-MMP, AtPCC1, AtMYB56, AtPELPK1, and AtPRP10, were significantly up-regulated in all complementary and overexpressing lines of Arabidopsis. Meanwhile, the results of RNA-seq showed that 69 and 33 differentially expressed genes (DEGs) were up- and down-regulated in transgenic rice, respectively. Four flowering-related genes, namely OsGA20OX1, OsCCR19, OsBTBN19, and OsRNS4 were significantly up-regulated in transgenic lines. To sum up, our findings demonstrate that ZmBES1/BZR1-9 is involved in controlling flowering and provide insights into further underlying roles of BES1/BZR1s in regulating growth and development in crops.

Brassinosteroids Regulate the Water Deficit and Latex Yield of Rubber Trees

Brassinolide (BR) is an important plant hormone that regulates the growth and development of plants and the formation of yield. The yield and quality of latex from Hevea brasiliensis are regulated by phytohormones. The understanding of gene network regulation mechanism of latex formation in rubber trees is still very limited. In this research, the rubber tree variety CATAS73397 was selected to analyze the relationship between BR, water deficit resistance, and latex yield. The results showed that BR improves the vitality of rubber trees under water deficit by increasing the rate of photosynthesis, reducing the seepage of osmotic regulatory substances, increasing the synthesis of energy substances, and improving the antioxidant system. Furthermore, BR increased the yield and quality of latex by reducing the plugging index and elevating the lutoid bursting index without decreasing mercaptan, sucrose, and inorganic phosphorus. This was confirmed by an increased expression of genes related to latex flow. RNA-seq analysis further indicated that DEG encoded proteins were enriched in the MAPK signaling pathway, plant hormone signal transduction and sucrose metabolism. Phytohormone content displayed significant differences, in that trans-Zeatin, ethylene, salicylic acid, kinetin, and cytokinin were induced by BR, whereas auxin, abscisic acid, and gibberellin were not. In summary, the current research lays a foundation for comprehending the molecular mechanism of latex formation in rubber trees and explores the potential candidate genes involved in natural rubber biosynthesis to provide useful information for further research in relevant areas.

Regulatory Effects of ABA and GA on the Expression of Conglutin Genes and LAFL Network Genes in Yellow Lupine (Lupinus luteus L.) Seeds

The maturation of seeds is a process of particular importance both for the plant itself by assuring the survival of the species and for the human population for nutritional and economic reasons. Controlling this process requires a strict coordination of many factors at different levels of the functioning of genetic and hormonal changes as well as cellular organization. One of the most important examples is the transcriptional activity of the LAFL gene regulatory network, which includes LEAFY COTYLEDON1 (LEC1) and LEC1-LIKE (L1L) and ABSCISIC ACID INSENSITIVE3 (ABI3), FUSCA3 (FUS3), and LEC2 (LEAFY COTYLEDON2), as well as hormonal homeostasis-of abscisic acid (ABA) and gibberellins (GA) in particular. From the nutritional point of view, the key to seed development is the ability of seeds to accumulate large amounts of proteins with different structures and properties. The world's food deficit is mainly related to shortages of protein, and taking into consideration the environmental changes occurring on Earth, it is becoming necessary to search for a way to obtain large amounts of plant-derived protein while maintaining the diversity of its origin. Yellow lupin, whose storage proteins are conglutins, is one of the plant species native to Europe that accumulates large amounts of this nutrient in its seeds. In this article we have shown the key changes occurring in the developing seeds of the yellow-lupin cultivar Taper by means of modern molecular biology techniques, including RNA-seq, chromatographic techniques and quantitative PCR analysis. We identified regulatory genes fundamental to the seed-filling process, as well as genes encoding conglutins. We also investigated how exogenous application of ABA and GA3 affects the expression of LlLEC2, LlABI3, LlFUS3, and genes encoding β- and δ-conglutins and whether it results in the amount of accumulated seed storage proteins. The research shows that for each species, even related plants, very specific changes can be identified. Thus the analysis and possibility of using such an approach to improve and stabilize yields requires even more detailed and extended research.

DELLA proteins positively regulate seed size in Arabidopsis

Human and animal nutrition is mainly based on seeds. Seed size is a key factor affecting seed yield and has thus been one of the primary objectives of plant breeders since the domestication of crop plants. Seed size is coordinately regulated by signals of maternal and zygotic tissues that control the growth of the seed coat, endosperm and embryo. Here, we provide previously unreported evidence for the role of DELLA proteins, key repressors of gibberellin responses, in the maternal control of seed size. The gain-of-function della mutant gai-1 produces larger seeds as a result of an increase in the cell number in ovule integuments. This leads to an increase in ovule size and, in turn, to an increase in seed size. Moreover, DELLA activity promotes increased seed size by inducing the transcriptional activation of AINTEGUMENTA, a genetic factor that controls cell proliferation and organ growth, in the ovule integuments of gai-1. Overall, our results indicate that DELLA proteins are involved in the control of seed size and suggest that modulation of the DELLA-dependent pathway could be used to improve crop yield.

GSK3 phosphorylates and regulates the Green Revolution protein Rht-B1b to reduce plant height in wheat

The utilization of stabilized DELLA proteins Rht-B1b and Rht-D1b was crucial for increasing wheat (Triticum aestivum) productivity during the Green Revolution. However, the underlying mechanisms remain to be clarified. Here, we cloned a gain-of-function allele of the GSK3/SHAGGY-like kinase-encoding gene GSK3 by characterizing a dwarf wheat mutant. Furthermore, we determined that GSK3 interacts with and phosphorylates the Green Revolution protein Rht-B1b to promote it to reduce plant height in wheat. Specifically, phosphorylation by GSK3 may enhance the activity and stability of Rht-B1b, allowing it to inhibit the activities of its target transcription factors. Taken together, we reveal a positive regulatory mechanism for the Green Revolution protein Rht-B1b by GSK3, which might have contributed to the Green Revolution in wheat.

Transcriptomic analysis of Chinese yam (Dioscorea polystachya Turcz.) variants indicates brassinosteroid involvement in tuber development

Dioscorea is an important but underutilized genus of flowering plants that grows predominantly in tropical and subtropical regions. Several species, known as yam, develop large underground tubers and aerial bulbils that are used as food. The Chinese yam (D. polystachya Turcz.) is one of the few Dioscorea species that grows well in temperate regions and has been proposed as a climate-resilient crop to enhance food security in Europe. However, the fragile, club-like tubers are unsuitable for mechanical harvesting, which is facilitated by shorter and thicker storage organs. Brassinosteroids (BRs) play a key role in plant cell division, cell elongation and proliferation, as well as in the gravitropic response. We collected RNA-Seq data from the head, middle and tip of two tuber shape variants: F60 (long, thin) and F2000 (short, thick). Comparative transcriptome analysis of F60 vs. F2000 revealed 30,229 differentially expressed genes (DEGs), 1,393 of which were differentially expressed in the growing tip. Several DEGs are involved in steroid/BR biosynthesis or signaling, or may be regulated by BRs. The quantification of endogenous BRs revealed higher levels of castasterone (CS), 28-norCS, 28-homoCS and brassinolide in F2000 compared to F60 tubers. The highest BR levels were detected in the growing tip, and CS was the most abundant (439.6 ± 196.41 pmol/g in F2000 and 365.6 ± 112.78 pmol/g in F60). Exogenous 24-epi-brassinolide (epi-BL) treatment (20 nM) in an aeroponic system significantly increased the width-to-length ratio (0.045 ± 0.002) compared to the mock-treated plants (0.03 ± 0.002) after 7 weeks, indicating that exogenous epi-BL produces shorter and thicker tubers. In this study we demonstrate the role of BRs in D. polystachya tuber shape, providing insight into the role of plant hormones in yam storage organ development. We found that BRs can influence tuber shape in Chinese yam by regulating the expression of genes involved cell expansion. Our data can help to improve the efficiency of Chinese yam cultivation, which could provide an alternative food source and thus contribute to future food security in Europe.

Genome-Wide Identification of BES1 Gene Family in Six Cucurbitaceae Species and Its Expression Analysis in Cucurbita moschata

The BES1 (BRI1-EMSSUPPRESSOR1) gene family play a vital role in the BR (brassinosteroid) signaling pathway, which is involved in the growth and development, biotic, abiotic, and hormone stress response in many plants. However, there are few reports of BES1 in Cucurbita moschata. In this study, 50 BES1 genes were identified in six Cucurbitaceae species by genome-wide analysis, which could be classified into 3 groups according to their gene structural features and motif compositions, and 13 CmoBES1 genes in Cucurbita moschata were mapped on 10 chromosomes. Quantitative real-time PCR analysis showed that the CmoBES1 genes displayed differential expression under different abiotic stress and hormone treatments. Subcellular localization showed that the most of CmoBES1 proteins localized in nucleus and cytoplasm, and transactivation assay indicated 9 CmoBES1 proteins played roles as transcription factors. Our analysis of BES1s diversity, localization, and expression in Curcubitaceae contributes to the better understanding of the essential roles of these transcription factors in plants.

CRISPR/Cas9 genome-editing applied to MdPGT1 in apple results in reduced foliar phloridzin without impacting plant growth

Phloridzin is the most abundant polyphenolic compound in apple (Malus × domestica Borkh.), which results from the action of a key phloretin-specific UDP-2'-O-glucosyltransferase (MdPGT1). Here, we simultaneously assessed the effects of targeting MdPGT1 by conventional transgenesis and clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9)-mediated genome editing. To this end, we conducted transcriptomic and metabolic analyses of MdPGT1 RNA interference knockdown and genome-edited lines. Knockdown lines exhibited characteristic impairment of plant growth and leaf morphology, whereas genome-edited lines exhibited normal growth despite reduced foliar phloridzin. RNA-sequencing analysis identified a common core of regulated genes, involved in phenylpropanoid and flavonoid pathways. However, we identified genes and processes differentially modulated in stunted and genome-edited lines, including key transcription factors and genes involved in phytohormone signalling. Therefore, we conducted a phytohormone profiling to obtain insight into their role in the phenotypes observed. We found that salicylic and jasmonic acid were increased in dwarf lines, whereas auxin and ABA showed no correlation with the growth phenotype. Furthermore, bioactive brassinosteroids were commonly up-regulated, whereas gibberellin GA₄ was distinctively altered, showing a sharp decrease in RNA interference knockdown lines. Expression analysis by reverse transcriptase-quantitative polymerase chain reaction expression analysis further confirmed transcriptional regulation of key factors involved in brassinosteroid and gibberellin interaction. These findings suggest that a differential modulation of phytohormones may be involved in the contrasting effects on growth following phloridzin reduction. The present study also illustrates how CRISPR/Cas9 genome editing can be applied to dissect the contribution of genes involved in phloridzin biosynthesis in apple.

GA-Mediated Disruption of RGA/BZR1 Complex Requires HSP90 to Promote Hypocotyl Elongation

Circuitries of signaling pathways integrate distinct hormonal and environmental signals, and influence development in plants. While a crosstalk between brassinosteroid (BR) and gibberellin (GA) signaling pathways has recently been established, little is known about other components engaged in the integration of the two pathways. Here, we provide supporting evidence for the role of HSP90 (HEAT SHOCK PROTEIN 90) in regulating the interplay of the GA and BR signaling pathways to control hypocotyl elongation of etiolated seedlings in Arabidopsis. Both pharmacological and genetic depletion of HSP90 alter the expression of GA biosynthesis and catabolism genes. Major components of the GA pathway, like RGA (REPRESSOR of ga1-3) and GAI (GA-INSENSITIVE) DELLA proteins, have been identified as physically interacting with HSP90. Interestingly, GA-promoted DELLA degradation depends on the ATPase activity of HSP90, and inhibition of HSP90 function stabilizes the DELLA/BZR1 (BRASSINAZOLE-RESISTANT 1) complex, modifying the expression of downstream transcriptional targets. Our results collectively reveal that HSP90, through physical interactions with DELLA proteins and BZR1, modulates DELLA abundance and regulates the expression of BZR1-dependent transcriptional targets to promote plant growth.

Signaling events for photomorphogenic root development

A germinating seedling incorporates environmental signals such as light into developmental outputs. Light is not only a source of energy, but also a central coordinative signal in plants. Traditionally, most research focuses on aboveground organs' response to light; therefore, our understanding of photomorphogenesis in roots is relatively scarce. However, root development underground is highly responsive to light signals from the shoot and understanding these signaling mechanisms will give a better insight into early seedling development. Here, we review the central light signaling hubs and their role in root growth promotion of Arabidopsis thaliana seedlings.

Rice DWARF AND LOW-TILLERING and the homeodomain protein OSH15 interact to regulate internode elongation via orchestrating brassinosteroid signaling and metabolism

Brassinosteroid (BR) phytohormones play crucial roles in regulating internode elongation in rice (Oryza sativa). However, the underlying mechanism remains largely unclear. The dwarf and low-tillering (dlt) mutant is a mild BR-signaling-defective mutant. Here, we identify two dlt enhancers that show more severe shortening of the lower internodes compared to the uppermost internode (IN1). Both mutants carry alleles of ORYZA SATIVA HOMEOBOX 15 (OSH15), the founding gene for dwarf6-type mutants, which have shortened lower internodes but not IN1. Consistent with the mutant phenotype, OSH15 expression is much stronger in lower internodes, particularly in IN2, than IN1. The osh15 single mutants have impaired BR sensitivity accompanied by enhanced BR synthesis in seedlings. DLT physically interacts with OSH15 to co-regulate many genes in seedlings and internodes. OSH15 targets and promotes the expression of the BR receptor gene BR INSENSITIVE1 (OsBRI1), and DLT facilitates this regulation in a dosage-dependent manner. In osh15, dlt, and osh15 dlt, BR levels are higher in seedlings and panicles, but unexpectedly lower in internodes compared with the wild-type. Taken together, our results suggest that DLT interacts with OSH15, which functions in the lower internodes, to modulate rice internode elongation via orchestrating BR signaling and metabolism.

PagDET2 promotes cambium cell division and xylem differentiation in poplar stem

Secondary growth of the woody tree stem is governed by meristematic cell division and differentiation in the vascular cambium. Multiple hormonal signals and endogenous developmental programs regulate vascular cambium activity. Brassinosteroids (BRs) significantly promote secondary stem growth and wood formation in poplar trees. However, the underlying regulatory mechanisms of BRs within the vascular tissue remain unclear. Genetic and anatomical approaches were used here to elucidate the role of PagDET2, the rate-limiting enzyme for BRs biosynthesis, in regulating secondary vascular cambium activity in Populus. This study showed that the elevated endogenous castasterone (CS) levels in tree stems through overexpressing PagDET2 could enhance cambium meristem cell activity and xylem (XY) differentiation to promote secondary stem growth. RNA-seq analysis revealed that genes involved in BRs response, vascular cambium cell division, XY differentiation, and secondary cell wall synthesis were up-regulated.

SlCESTA Is a Brassinosteroid-Regulated bHLH Transcription Factor of Tomato That Promotes Chilling Tolerance and Fruit Growth When Over-Expressed

Brassinosteroids (BRs) are required for various aspects of plant growth and development, but also participate in stress responses. The hormones convey their activity through transcriptional regulation and posttranslational modification of transcription factors and one class are basic helix-loop-helix (bHLH) proteins of the BR Enhanced Expression (BEE) subfamily, which in Arabidopsis thaliana include BEE1-3 and CESTA (CES). CES and the BEEs promote the expression of different BR-responsive genes, including genes encoding gibberellin (GA) biosynthetic and catabolizing enzymes, as well as cold-responsive genes. Interestingly, in terms of an application, CES could promote both fruit growth and cold stress tolerance when over-expressed in A. thaliana and here it was investigated, if this function is conserved in the fruit crop Solanum lycopersicum (cultivated tomato). Based on amino acid sequence similarity and the presence of regulatory motifs, a CES orthologue of S. lycopersicum, SlCES, was identified and the effects of its over-expression were analysed in tomato. This showed that SlCES, like AtCES, was re-localized to nuclear bodies in response to BR signaling activation and that it effected GA homeostasis, with related phenotypes, when over-expressed. In addition, over-expression lines showed an increased chilling tolerance and had altered fruit characteristics. The possibilities and potential limitations of a gain of SlCES function as a breeding strategy for tomato are discussed.

Species-Specific Variation in Abscisic Acid Homeostasis and Responses Impacts Important Traits in Crassocephalum Orphan Crops

Crassocephalum rubens and Crassocephalum crepidioides are plant species native to Africa, but grow in most tropical and subtropical regions of the world. They are rich in vitamins, minerals, and essential oils and are traditional leafy vegetables and medicinal plants in Sub-Saharan Africa. The plants are still mainly collected from the wild but shall be taken into cultivation and an important aim in the domestication of these species is to improve traits that are relevant for crop production. Here, seed formation and germination capacities in C. crepidioides and C. rubens were investigated, and it was found that C. crepidioides exhibits a higher level of seed dormancy, which could be broken with light, and was correlated with higher amounts of abscisic acid (ABA), a plant hormone that promotes seed dormancy. ABA is also very well-known for its role in abiotic stress tolerance, and it is shown that tetraploid C. crepidioides exhibits a higher level of resistance against drought and heat stress than diploid C. rubens, traits that will benefit the cultivation of these plants, particularly in rain-fed cropping systems. The potential of Crassocephalum to improve nutrition and increase the resilience of marginal cropping systems in Africa is discussed.

Molecular Regulation of Antioxidant Melatonin Biosynthesis by Brassinosteroid Acting as an Endogenous Elicitor of Melatonin Induction in Rice Seedlings

Gibberellic acid (GA) was recently shown to induce melatonin synthesis in rice. Here, we examined whether brassinosteroids (BRs) also induce melatonin synthesis because BRs and GA show redundancy in many functions. Among several plant hormones, exogenous BR treatment induced melatonin synthesis by twofold compared to control treatment, whereas ethylene, 6-benzylaminopurine (BA), and indole-3-acetic acid (IAA) showed negligible effects on melatonin synthesis. Correspondingly, BR treatment also induced a number of melatonin biosynthetic genes in conjunction with the suppression of melatonin catabolic gene expression. Several transgenic rice plants with downregulated BR biosynthesis-related genes, such as DWARF4, DWARF11, and RAV-Like1 (RAVL1), were generated and exhibited decreased melatonin synthesis, indicating that BRs act as endogenous elicitors of melatonin synthesis. Notably, treatment with either GA or BR fully restored melatonin synthesis in the presence of paclobutrazol, a GA biosynthesis inhibitor. Moreover, exogenous BR treatment partially restored melatonin synthesis in both RAVL1 and Gα RNAi transgenic rice plants, whereas GA treatment fully restored melatonin synthesis comparable to wild type in RAVL1 RNAi plants. Taken together, our results highlight a role of BR as an endogenous elicitor of melatonin synthesis in a GA-independent manner in rice plants.

Tomato SlBES1.8 Influences Leaf Morphogenesis by Mediating Gibberellin Metabolism and Signaling

Leaf morphogenetic activity determines its shape diversity. However, our knowledge of the regulatory mechanism in maintaining leaf morphogenetic capacity is still limited. In tomato, gibberellin (GA) negatively regulates leaf complexity by shortening the morphogenetic window. We here report a tomato BRI1-EMS-suppressor 1 transcription factor, SlBES1.8, that promoted the simplification of leaf pattern in a similar manner as GA functions. OE-SlBES1.8 plants exhibited reduced sensibility to exogenous GA3 treatment whereas showed increased sensibility to the application of GA biosynthesis inhibitor, paclobutrazol. In line with the phenotypic observation, the endogenous bioactive GA contents were increased in OE-SlBES1.8 lines, which certainly promoted the degradation of the GA signaling negative regulator, SlDELLA. Moreover, transcriptomic analysis uncovered a set of overlapping genomic targets of SlBES1.8 and GA, and most of them were regulated in the same way. Expression studies showed the repression of SlBES1.8 to the transcriptions of two GA-deactivated genes, SlGA2ox2 and SlGA2ox6, and one GA receptor, SlGID1b-1. Further experiments confirmed the direct regulation of SlBES1.8 to their promoters. On the other hand, SlDELLA physically interacted with SlBES1.8 and further inhibited its transcriptional regulation activity by abolishing SlBES1.8-DNA binding. Conclusively, by mediating GA deactivation and signaling, SlBES1.8 greatly influenced tomato leaf morphogenesis.

Potential roles of melatonin and ABA on apple dwarfing in semi-arid area of Xinjiang China

Dwarfing is a typic breeding trait for mechanical strengthening and relatively high yield in modern apple orchards. Clarification of the mechanisms associated with dwarfing is important for use of molecular technology to breed apple. Herein, we identified four dwarfing apple germplasms in semi-arid area of Xinjiang, China. The internodal distance of these four germplasms were significantly shorter than non-dwarfing control. Their high melatonin (MT) contents are negatively associated with their malondialdehyde (MDA) levels and oxidative damage. In addition, among the detected hormones including auxin (IAA), gibberellin (GA), brassinolide (BR), zeatin-riboside (ZR), and abscisic acid (ABA), only ABA and ZR levels were in good correlation with the dwarfing phenotype. The qPCR results showed that the expression of melatonin synthetic enzyme genes MdASMT1 and MdSNAT5, ABA synthetic enzyme gene MdAAO3 and degradative gene MdCYP707A, ZR synthetic enzyme gene MdIPT5 all correlated well with the enhanced levels of MT, ABA and the reduced level of of ZR in the dwarfing germplasms. Furthermore, the significantly higher expression of ABA marker genes (MdRD22 and MdRD29) and the lower expression of ZR marker genes (MdRR1 and MdRR2) in all the four dwarf germplasms were consistent with the ABA and ZR levels. Considering the yearly long-term drought occurring in Xinjiang, China, it seems that dwarfing with high contents of MT and ABA may be a good strategy for these germplasms to survive against drought stress. This trait of dwarfing may also benefit apple production and breeding in this semi-arid area.

Brassinosteroid-regulated bHLH transcription factor CESTA induces the gibberellin 2-oxidase GA2ox7

Brassinosteroids (BRs) are plant steroids that have growth-promoting capacities, which are partly enabled by an ability to induce biosynthesis of gibberellins (GAs), a second class of plant hormones. In addition, BRs can also activate GA catabolism; here we show that in Arabidopsis (Arabidopsis thaliana) the basic helix-loop-helix transcription factor CESTA (CES) and its homologues BRASSINOSTEROID-ENHANCED EXPRESSION (BEE) 1 and 3 contribute to this activity. CES and the BEEs are BR-regulated at the transcriptional and posttranslational level and participate in different physiological processes, including vegetative and reproduction development, shade avoidance, and cold stress responses. We show that CES/BEEs can induce the expression of the class III GA 2-oxidase GA2ox7 and that this activity is increased by BRs. In BR signaling - and CES/BEE-deficient mutants, GA2ox7 expression decreased, yielding reduced levels of GA110, a product of GA2ox7 activity. In plants that over-express CES, GA2ox7 expression is hyper-responsive to BR, GA110 levels are elevated and amounts of bioactive GA are reduced. We provide evidence that CES directly binds to the GA2ox7 promoter and is activated by BRs, but can also act by BR-independent means. Based on these results, we propose a model for CES activity in GA catabolism where CES can be recruited for GA2ox7 induction not only by BR, but also by other factors.

Interactions of Gibberellins with Phytohormones and Their Role in Stress Responses

Gibberellins are amongst the main plant growth regulators. Discovered over a century ago, the interest in gibberellins research is growing due to their current and potential applications in crop production and their role in the responses to environmental stresses. In the present review, the current knowledge on gibberellins’ homeostasis and modes of action is outlined. Besides this, the complex interrelations between gibberellins and other plant growth regulators are also described, providing an intricate network of interactions that ultimately drives towards precise and specific gene expression. Thus, genes and proteins identified as being involved in gibberellin responses in model and non-model species are highlighted. Furthermore, the molecular mechanisms governing the gibberellins’ relation to stress responses are also depicted. This review aims to provide a comprehensive picture of the state-of-the-art of the current perceptions of the interactions of gibberellins with other phytohormones, and their responses to plant stresses, thus allowing for the identification of the specific mechanisms involved. This knowledge will help us to improve our understanding of gibberellins’ biology, and might help increase the biotechnological toolbox needed to refine plant resilience, particularly under a climate change scenario.

Transcriptome analysis of pod mutant reveals plant hormones are important regulators in controlling pod size in peanut (Arachis hypogaea L.)

Pod size is an important yield-influencing trait in peanuts. It is affected by plant hormones and identifying the genes related to these hormones may contribute to pod-related trait improvements in peanut breeding programs. However, there is limited information on the molecular mechanisms of plant hormones that regulate pod size in peanuts. We identified a mutant with an extremely small pod (spm) from Yuanza 9102 (WT) by ⁶⁰Co γ-radiation mutagenesis. The length and width of the natural mature pod in spm were only 71.34% and 73.36% of those in WT, respectively. We performed comparative analyses for morphological characteristics, anatomy, physiology, and global transcriptome between spm and WT pods. Samples were collected at 10, 20, and 30 days after peg elongation into the soil, representing stages S1, S2, and S3, respectively. The differences in pod size between WT and spm were seen at stage S1 and became even more striking at stages S2 and S3. The cell sizes of the pods were significantly smaller in spm than in WT at stages S1, S2, and S3. These results suggested that reduced cell size may be one of the important contributors for the small pod in spm. The contents of indole-3-acetic acid (IAA), gibberellin (GA), and brassinosteroid (BR) were also significantly lower in spm pods than those in WT pods at all three stages. RNA-Seq analyses showed that 1,373, 8,053, and 3,358 differently expressed genes (DEGs) were identified at stages S1, S2, and S3, respectively. Functional analyses revealed that a set of DEGs was related to plant hormone biosynthesis, plant hormone signal transduction pathway, and cell wall biosynthesis and metabolism. Furthermore, several hub genes associated with plant hormone biosynthesis and signal transduction pathways were identified through weighted gene co-expression network analysis. Our results revealed that IAA, GA, and BR may be important regulators in controlling pod size by regulating cell size in peanuts. This study provides helpful information for the understanding of the complex mechanisms of plant hormones in controlling pod size by regulating the cell size in peanuts and will facilitate the improvement of peanut breeding.

Exogenous Gibberellin Treatment Enhances Melatonin Synthesis for Melatonin-Enriched Rice Production

Melatonin production is induced by many abiotic and biotic stressors; it modulates the levels of many plant hormones and their signaling pathways. This study investigated the effects of plant hormones on melatonin synthesis. Melatonin synthesis in rice seedlings was significantly induced upon exogenous gibberellin 3 (GA₃) treatment, while it was severely decreased by GA synthesis inhibitor paclobutrazol. In contrast, abscisic acid (ABA) strongly inhibited melatonin synthesis, whereas its inhibitor norflurazon (NF) induced melatonin synthesis. The observed GA-mediated increase in melatonin was closely associated with elevated expression levels of melatonin biosynthetic genes such as TDC3, T5H, and ASMT1; it was also associated with reduced expression levels of catabolic genes ASDAC and M2H. In a paddy field, the treatment of immature rice seeds with exogenous GA led to enhanced melatonin production in rice seeds; various transgenic rice plants downregulating a GA biosynthesis gene (GA3ox2) and a signaling gene (Gα) showed severely decreased melatonin levels, providing in vivo genetic evidence that GA has a positive effect on melatonin synthesis. This is the first study to report that GA is positively involved in melatonin synthesis in plants; GA treatment can be used to produce melatonin-rich seeds, vegetables, and fruits, which are beneficial for human health.

Transcription factor BES1 interacts with HSFA1 to promote heat stress resistance of plants

Heat stress is a major environmental stress type that can limit plant growth and development. To survive sudden temperature increases, plants utilize the heat shock response, an ancient signaling pathway. Initial results had suggested a role for brassinosteroids (BRs) in this response. Brassinosteroids are growth-promoting steroid hormones whose activity is mediated by transcription factors of the BES1/BZR1 subfamily. Here, we provide evidence that BES1 can contribute to heat stress signaling. In response to heat, BES1 is activated even in the absence of BRs and directly binds to heat shock elements (HSEs), known binding sites of heat shock transcription factors (HSFs). HSFs of the HSFA1 type can interact with BES1 and facilitate its activity in HSE binding. These findings lead us to propose an extended model of the heat stress response in plants, in which the recruitment of BES1 is a means of heat stress signaling cross-talk with a central growth regulatory pathway.

Integrated regulation of periclinal cell division by transcriptional module of BZR1-SHR in Arabidopsis roots

The timing and extent of cell division are crucial for the correct patterning of multicellular organism. In Arabidopsis, root ground tissue maturation involves the periclinal cell division of the endodermis to generate two cell layers: endodermis and middle cortex. However, the molecular mechanism underlying this pattern formation remains unclear. Here, we report that phytohormone brassinosteroid (BR) and redox signal hydrogen peroxide (H₂ O₂ ) interdependently promote periclinal division during root ground tissue maturation by regulating the activity of SHORT-ROOT (SHR), a master regulator of root growth and development. BR-activated transcription factor BRASSINAZOLE RESISTANT1 (BZR1) directly binds to the promoter of SHR to induce its expression, and physically interacts with SHR to increase the transcripts of RESPIRATORY BURST OXIDASE HOMOLOGs (RBOHs) and elevate the levels of H₂ O₂ , which feedback enhances the interaction between BZR1 and SHR. Additionally, genetic analysis shows that SHR is required for BZR1-promoted periclinal division, and BZR1 enhances the promoting effects of SHR on periclinal division. Together, our finding reveals that the transcriptional module of BZR1-SHR fine-tunes periclinal division during root ground tissue maturation in response to hormone and redox signals.

Interaction between BZR1 and EIN3 mediates signalling crosstalk between brassinosteroids and ethylene

Plant growth and development are coordinated by multiple environmental and endogenous signals. Brassinosteroid (BR) and ethylene (ET) have overlapping functions in a wide range of developmental processes. However, the relationship between the BR and ET signalling pathways has remained unclear. Here, we show that BR and ET interdependently promote apical hook development and cell elongation through a direct interaction between BR-activated BRASSINOZALE-RESISTANT1 (BZR1) and ET-activated ETHYLENE INSENSITIVE3 (EIN3). Genetic analysis showed that BR signalling is required for ET promotion of apical hook development in the dark and cell elongation under light, and ET quantitatively enhances BR-potentiated growth. BZR1 interacts with EIN3 to co-operatively increase the expression of HOOKLESS1 and PACLOBUTRAZOL RESISTANCE FACTORs (PREs). Furthermore, we found that BR promotion of hook development requires gibberellin (GA), and GA restores the hookless phenotype of BR-deficient materials by activating EIN3/EIL1. Our findings shed light on the molecular mechanism underlying the regulation of plant development by BR, ET and GA signals through the direct interaction of master transcriptional regulators.

Genome-wide identification and characterization of the BES/BZR gene family in wheat and foxtail millet

Background

BES/BZR family genes have vital roles in plant growth, development, and adaptation to environmental stimuli. However, they have not yet been characterized and systematically analyzed in wheat and foxtail millet.

Results

In the current study, five common and two unique BES/BZR genes were identified by genome-wide analysis in wheat and foxtail millet, respectively. These genes were unevenly distributed on 14 and five chromosomes of wheat and foxtail millet, respectively, and clustered in two subgroups in a phylogenetic analysis. The BES/BZR gene family members in each subgroup contained similar conserved motifs. Investigation of cis-acting elements and expression profile analysis revealed that the BES/BZR genes were predominantly expressed in leaf tissues of wheat and foxtail millet seedlings and responded to brassinosteroid, abscisic acid, and NaCl treatments.

Conclusions

Our results provide a basis for future studies on the function and molecular mechanisms of the BES/BZR gene family in wheat, foxtail millet, and other plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08002-5.

Endogenous level of abscisic acid down-regulated by brassinosteroids signaling via BZR1 to control the growth of Arabidopsis thaliana

The increased level of endogenous abscisic acid (ABA) in brassinosteroid (BR)-deficient mutants, such as det2 and cyp85a1 × cyp85a2, suggests that ABA synthesis is inhibited by endogenous BRs in Arabidopsis thaliana. Expression of the ABA biosynthesis gene ABA-deficient 2 (ABA2) was negatively regulated by exogenously applied BR but up-regulated by the application of brassinazole and in det2 and cyp85a1 × cyp85a2. In addition, ABA2 expression decreased in bzr1-1D, showing that ABA biosynthesis is inhibited by BR signaling via BZR1, intermediated by ABA2, in Arabidopsis. Four cis-element sequences (E-boxes 1-4) in the putative promoter region of ABA2 were identified as BZR1 binding sites. The electrophoretic mobility shift assay and chromatin immune precipitation analysis demonstrated that BZR1 directly binds to overlapped E-boxes (E-box 3/4) in the promoter region of ABA2. The level of endogenous ABA was decreased in bzr1-1D compared to wild-type, indicating that binding of BZR1 to the ABA2 promoter inhibits ABA synthesis in Arabidopsis. Compared to wild-type, aba2-1 exhibited severely reduced growth and development. The abnormalities in aba2-1 were rescued by the application of ABA, suggesting that ABA2 expression and ABA synthesis are necessary for the normal growth and development of A. thaliana. Finally, bzr1-KO × aba2-1 exhibited inhibitory growth of primary roots compared to bzr1-KO, verifying that ABA2 is a downstream target of BZR1 in the plant. Taken together, the level of endogenous ABA is down-regulated by BR signaling via BZR1, controlling the growth of A. thaliana.

Two Auxinic Herbicides Affect Brassica napus Plant Hormone Levels and Induce Molecular Changes in Transcription

With the introduction of the new auxinic herbicide halauxifen-methyl into the oilseed rape (Brassica napus) market, there is a need to understand how this new molecule interacts with indigenous plant hormones (e.g., IAA) in terms of crop response. The aim of this study was to investigate the molecular background by using different growth conditions under which three different auxinic herbicides were administered. These were halauxifen-methyl (Hal), alone and together with aminopyralid (AP) as well as picloram (Pic). Three different hormone classes were determined, free and conjugated indole-3-acetic acid (IAA), aminocyclopropane carboxylic acid (ACC) as a precursor for ethylene, and abscisic acid (ABA) at two different temperatures and growth stages as well as over time (2–168 h after treatment). At 15 °C growth temperature, the effect was more pronounced than at 9 °C, and generally, the younger leaves independent of the developmental stage showed a larger effect on the alterations of hormones. IAA and ACC showed reproducible alterations after auxinic herbicide treatments over time, while ABA did not. Finally, a transcriptome analysis after treatment with two auxinic herbicides, Hal and Pic, showed different expression patterns. Hal treatment leads to the upregulation of auxin and hormone responses at 48 h and 96 h. Pic treatment induced the hormone/auxin response already after 2 h, and this continued for the other time points. The more detailed analysis of the auxin response in the datasets indicate a role for GH3 genes and genes encoding auxin efflux proteins. The upregulation of the GH3 genes correlates with the increase in conjugated IAA at the same time points and treatments. Also, genes for were found that confirm the upregulation of the ethylene pathway.

Leaf direction: Lamina joint development and environmental responses

Plant architecture plays a major role in canopy photosynthesis and biomass production, and plants adjust their growth (and thus architecture) in response to changing environments. Leaf angle is one of the most important traits in rice (Oryza sativa L.) plant architecture, because leaf angle strongly affects leaf direction and rice production, with more-erect leaves being advantageous for high-density plantings. The degree of leaf bending depends on the morphology of the lamina joint, which connects the leaf and the sheath. In this review, we discuss cell morphology in different lamina joint tissues and describe the underlying genetic network that governs this morphology and thus regulates leaf direction. Furthermore, we focus on the mechanism by how environmental factors influence rice leaf angle. Our review provides a theoretical framework for the future genetic improvement of rice leaf orientation and plant architecture.

The Orphan Crop Crassocephalum crepidioides Accumulates the Pyrrolizidine Alkaloid Jacobine in Response to Nitrogen Starvation

Crassocephalum crepidioides is an African orphan crop that is used as a leafy vegetable and medicinal plant. Although it is of high regional importance in Sub-Saharan Africa, the plant is still mainly collected from the wild and therefore efforts are made to promote its domestication. However, in addition to beneficial properties, there was first evidence that C. crepidioides can accumulate the highly toxic pyrrolizidine alkaloid (PA) jacobine and here it was investigated, how jacobine production is controlled. Using ecotypes from Africa and Asia that were characterized in terms of their PA profiles, it is shown that the tetraploid C. crepidioides forms jacobine, an ability that its diploid close relative Crassocephalum rubens appears to lack. Evidence is provided that nitrogen (N) deficiency strongly increases jacobine in the leaves of C. crepidioides, that this capacity depends more strongly on the shoot than the root system, and that homospermidine synthase (HSS) activity is not rate-limiting for this reaction. A characterization of HSS gene representation and transcription showed that C. crepidioides and C. rubens possess two functional versions, one of which is conserved, that the HSS transcript is mainly present in roots and that its abundance is not controlled by N deficiency. In summary, this work improves our understanding of how environmental cues impact PA biosynthesis in plants and provides a basis for the development of PA-free C. crepidioides cultivars, which will aid its domestication and safe use.

Exogenous Brassinosteroid Facilitates Xylem Development in Pinus massoniana Seedlings

Brassinosteroids (BRs) are known to be essential regulators for wood formation in herbaceous plants and poplar, but their roles in secondary growth and xylem development are still not well-defined, especially in pines. Here, we treated Pinus massoniana seedlings with different concentrations of exogenous BRs, and assayed the effects on plant growth, xylem development, endogenous phytohormone contents and gene expression within stems. Application of exogenous BR resulted in improving development of xylem more than phloem, and promoting xylem development in a dosage-dependent manner in a certain concentration rage. Endogenous hormone determination showed that BR may interact with other phytohormones in regulating xylem development. RNA-seq analysis revealed that some conventional phenylpropanoid biosynthesis- or lignin synthesis-related genes were downregulated, but the lignin content was elevated, suggesting that new lignin synthesis pathways or other cell wall components should be activated by BR treatment in P. massoniana. The results presented here reveal the foundational role of BRs in regulating plant secondary growth, and provide the basis for understanding molecular mechanisms of xylem development in P. massoniana.

Brassinosteroids repress the seed maturation program during the seed-to-seedling transition

In flowering plants, repression of the seed maturation program is essential for the transition from the seed to the vegetative phase, but the underlying mechanisms remain poorly understood. The B3-domain protein VIVIPAROUS1/ABSCISIC ACID-INSENSITIVE3-LIKE 1 (VAL1) is involved in repressing the seed maturation program. Here we uncovered a molecular network triggered by the plant hormone brassinosteroid (BR) that inhibits the seed maturation program during the seed-to-seedling transition in Arabidopsis (Arabidopsis thaliana). val1-2 mutant seedlings treated with a BR biosynthesis inhibitor form embryonic structures, whereas BR signaling gain-of-function mutations rescue the embryonic structure trait. Furthermore, the BR-activated transcription factors BRI1-EMS-SUPPRESSOR 1 and BRASSINAZOLE-RESISTANT 1 bind directly to the promoter of AGAMOUS-LIKE15 (AGL15), which encodes a transcription factor involved in activating the seed maturation program, and suppress its expression. Genetic analysis indicated that BR signaling is epistatic to AGL15 and represses the seed maturation program by downregulating AGL15. Finally, we showed that the BR-mediated pathway functions synergistically with the VAL1/2-mediated pathway to ensure the full repression of the seed maturation program. Together, our work uncovered a mechanism underlying the suppression of the seed maturation program, shedding light on how BR promotes seedling growth.

Pre-harvest sprouting in cereals: genetic and biochemical mechanisms

With the growth of the global population and the increasing frequency of natural disasters, crop yields must be steadily increased to enhance human adaptability to risks. Pre-harvest sprouting (PHS), a term mainly used to describe the phenomenon in which grains germinate on the mother plant directly before harvest, is a serious global problem for agricultural production. After domestication, the dormancy level of cultivated crops was generally lower than that of their wild ancestors. Although the shortened dormancy period likely improved the industrial performance of cereals such as wheat, barley, rice, and maize, the excessive germination rate has caused frequent PHS in areas with higher rainfall, resulting in great economic losses. Here, we systematically review the causes of PHS and its consequences, the major indicators and methods for PHS assessment, and emphasize the biological significance of PHS in crop production. Wheat quantitative trait loci functioning in the control of PHS are also comprehensively summarized in a meta-analysis. Finally, we use Arabidopsis as a model plant to develop more complete PHS regulatory networks for wheat. The integration of this information is conducive to the development of custom-made cultivated lines suitable for different demands and regions, and is of great significance for improving crop yields and economic benefits.

Exogenous application of brassinosteroids regulates tobacco leaf size and expansion via modulation of endogenous hormones content and gene expression

Brassinosteroids (BR) play diverse roles in the regulation of plant growth and development. BR promotes plant growth by triggering cell division and expansion. However, the effect of exogenous BR application on the leaf size and expansion of tobacco is unknown. Tobacco seedlings are treated with different concentrations of exogenous 2,4-epibrassinolide (EBL) [control (CK, 0 mol L^-1), T1 (0.5 × 10^-7 mol L^-1), and T2 (0.5 × 10^-4 mol L^-1)]. The results show that T1 has 17.29% and T2 has 25.99% more leaf area than control. The epidermal cell area is increased by 24.40% and 17.13% while the number of epidermal cells is 7.06% and 21.06% higher in T1 and T2, respectively, relative to control. So the exogenous EBL application improves the leaf area by increasing cell numbers and cell area. The endogenous BR (7.5 times and 68.4 times), auxin (IAA) (4.03% and 25.29%), and gibberellin (GA₃) contents (84.42% and 91.76%) are higher in T1 and T2, respectively, in comparison with control. Additionally, NtBRI1, NtBIN2, and NtBES1 are upregulated showing that the brassinosteroid signaling pathway is activated. Furthermore, the expression of the key biosynthesis-related genes of BR (NtDWF4), IAA (NtYUCCA6), and GA₃ (NtGA3ox-2) are all upregulated under EBL application. Finally, the exogenous EBL application also upregulated the expression of cell growth-related genes (NtCYCD3;1, NtARGOS, NtGRF5, NtGRF8, and NtXTH). The results reveal that the EBL application increases the leaf size and expansion by promoting the cell expansion and division through higher BR, IAA, and GA₃ contents along with the upregulation of cell growth-related genes. The results of the study provide a scientific basis for the effect of EBL on tobacco leaf growth at morphological, anatomical, biochemical, and molecular levels.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00971-x.