Enhancing Brassinosteroid Signaling via Overexpression of Tomato (Solanum lycopersicum) SlBRI1 Improves Major Agronomic Traits

Untargeted mutagenesis of brassinosteroid receptor SbBRI1 confers drought tolerance by altering phenylpropanoid metabolism in Sorghum bicolor

Drought is a critical issue in modern agriculture; therefore, there is a need to create crops with drought resilience. The complexity of plant responses to abiotic stresses, particularly in the field of brassinosteroid (BR) signalling, has been the subject of extensive research. In this study, we unveil compelling insights indicating that the BRASSINOSTEROID-INSENSITIVE 1 (BRI1) receptor in Arabidopsis and Sorghum plays a critical role as a negative regulator of drought responses. Introducing untargeted mutation in the sorghum BRI1 receptor (SbBRI1) effectively enhances the plant's ability to withstand osmotic and drought stress. Through DNA Affinity Purification sequencing (DAP-seq), we show that the sorghum BRI1-EMS-SUPPRESSOR 1 (SbBES1) transcription factor, a downstream player of the BR signalling, binds to a conserved G-box binding motif, and it is responsible for regulating BR homeostasis, as its Arabidopsis ortholog AtBES1. We further characterized the drought tolerance of sorghum bri1 mutants and decipher SbBES1-mediated regulation of phenylpropanoid pathway. Our findings suggest that SbBRI1 signalling serves a dual purpose: under normal conditions, it regulates lignin biosynthesis by SbBES1, but during drought conditions, BES1 becomes less active, allowing the activation of the flavonoid pathway. This adaptive shift improves the photosynthetic rate and photoprotection, reinforcing crop adaptation to drought.

Influence of exogenous 24-epibrassinolide on improving carotenoid content, antioxidant capacity and gene expression in germinated maize seeds

BACKGROUND

Carotenoids have various physiological functions, such as immune regulation and cancer prevention. Germination could further improve the content of carotenoids in maize seeds. In this study, yellow maize seeds (Suyu 29) were soaked and germinated with different concentrations of 24-epibrassinolide. The changes of germination percentage, sprout length, bioactive components, antioxidant capacity and carotenoid content of the maize seeds were analyzed. Additionally, the relative expression of key genes in the carotenoid synthesis pathway was investigated.

RESULTS

The results showed that the sprout length, germination percentage, soluble protein, free amino acids, proline, endogenous abscisic acid, vitamin C, total phenolics and carotenoids displayed a significant increasing trend compared with the control group (P < 0.05). The activity of superoxide dismutase and peroxidase increased by 55.1% and 58.5% versus the control group, and the antioxidant capacity of 2,2-diphenyl-1-picrylhydrazyl, 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) and ferric reducing antioxidant power was 19.8%, 13.4% and 44.1% higher than that of the control group (P < 0.05). Compared with the control group, the expression of genes was significantly up-regulated (P < 0.05). Under the treatment of 0.1 mg L-1 of 24-epibrassinolide, carotenoid content reached the highest value. The carotenoids showed a positive correspondence with antioxidant enzyme activity, antioxidant capacity and total phenolics content (P < 0.05).

CONCLUSION

This study showed that 0.1 mg L-1 of exogenous 24-epibrassinolide promoted the accumulation of carotenoids and improved the antioxidant capacity and the quality of germinated maize seeds. It could provide a method for the development of germinated maize products enriched in carotenoids. © 2024 Society of Chemical Industry.

The brassinosteroid receptor StBRI1 promotes tuber development by enhancing plasma membrane H+-ATPase activity in potato

The brassinosteroid (BR) receptor BRASSINOSTEROID-INSENSITIVE 1 (BRI1) plays a critical role in plant growth and development. Although much is known about how BR signaling regulates growth and development in many crop species, the role of StBRI1 in regulating potato (Solanum tuberosum) tuber development is not well understood. To address this question, a series of comprehensive genetic and biochemical methods were applied in this investigation. It was determined that StBRI1 and Solanum tuberosum PLASMA MEMBRANE (PM) PROTON ATPASE2 (PHA2), a PM-localized proton ATPase, play important roles in potato tuber development. The individual overexpression of StBRI1 and PHA2 led to a 22% and 25% increase in tuber yield per plant, respectively. Consistent with the genetic evidence, in vivo interaction analysis using double transgenic lines and PM H+-ATPase activity assays indicated that StBRI1 interacts with the C-terminus of PHA2, which restrains the intramolecular interaction of the PHA2 C-terminus with the PHA2 central loop to attenuate autoinhibition of PM H+-ATPase activity, resulting in increased PHA2 activity. Furthermore, the extent of PM H+-ATPase autoinhibition involving phosphorylation-dependent mechanisms corresponds to phosphorylation of the penultimate Thr residue (Thr-951) in PHA2. These results suggest that StBRI1 phosphorylates PHA2 and enhances its activity, which subsequently promotes tuber development. Altogether, our results uncover a BR-StBRI1-PHA2 module that regulates tuber development and suggest a prospective strategy for improving tuberous crop growth and increasing yield via the cell surface-based BR signaling pathway.

A tomato NAC transcription factor, SlNAP1, directly regulates gibberellin-dependent fruit ripening

In tomato (Solanum lycopersicum), the ripening of fruit is regulated by the selective expression of ripening-related genes, and this procedure is controlled by transcription factors (TFs). In the various plant-specific TF families, the no apical meristem (NAM), Arabidopsis thaliana activating factor 1/2 (ATAF1/2), and cup-shaped cotyledon 2 (CUC2; NAC) TF family stands out and plays a significant function in plant physiological activities, such as fruit ripening (FR). Despite the numerous genes of NAC found in the tomato genome, limited information is available on the effects of NAC members on FR, and there is also a lack of studies on their target genes. In this research, we focus on SlNAP1, which is a NAC TF that positively influences the FR of tomato. By employing CRISPR/Cas9 technology, compared with the wild type (WT), we generated slnap1 mutants and observed a delay in the ethylene production and color change of fruits. We employed the yeast one-hybrid (Y1H) and dual-luciferase reporter (DLR) assays to confirm that SlNAP1 directly binds to the promoters of two crucial genes involved in gibberellin (GA) degradation, namely SlGA2ox1 and SlGA2ox5, thus activating their expression. Furthermore, through a yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BIFC) and luciferase (LUC) assays, we established an interaction between SlNAP1 and SlGID1. Hence, our findings suggest that SlNAP1 regulates FR positively by activating the GA degradation genes directly. Additionally, the interaction between SlNAP1 and SlGID1 may play a role in SlNAP1-induced FR. Overall, our study provides important insights into the molecular mechanisms through which NAC TFs regulate tomato FR via the GA pathway.

Recent Advances in Studying the Regulation of Fruit Ripening in Tomato Using Genetic Engineering Approaches

Tomato (Solanum lycopersicum L.) is one of the most commercially essential vegetable crops cultivated worldwide. In addition to the nutritional value, tomato is an excellent model for studying climacteric fruits' ripening processes. Despite this, the available natural pool of genes that allows expanding phenotypic diversity is limited, and the difficulties of crossing using classical selection methods when stacking traits increase proportionally with each additional feature. Modern methods of the genetic engineering of tomatoes have extensive potential applications, such as enhancing the expression of existing gene(s), integrating artificial and heterologous gene(s), pointing changes in target gene sequences while keeping allelic combinations characteristic of successful commercial varieties, and many others. However, it is necessary to understand the fundamental principles of the gene molecular regulation involved in tomato fruit ripening for its successful use in creating new varieties. Although the candidate genes mediate ripening have been identified, a complete picture of their relationship has yet to be formed. This review summarizes the latest (2017-2023) achievements related to studying the ripening processes of tomato fruits. This work attempts to systematize the results of various research articles and display the interaction pattern of genes regulating the process of tomato fruit ripening.

Medium-chain-length polyprenol (C45-C55) formation in chloroplasts of Arabidopsis is brassinosteroid-dependent

Brassinosteroids are important plant hormones influencing, among other processes, chloroplast development, the electron transport chain during light reactions of photosynthesis, and the Calvin-Benson cycle. Medium-chain-length polyprenols built of 9-11 isoprenoid units (C45-C55 carbons) are a class of isoprenoid compounds present in abundance in thylakoid membranes. They are synthetized in chloroplast by CPT7 gene from Calvin cycle derived precursors on MEP (methylerythritol 4-phosphate) isoprenoid biosynthesis pathway. C45-C55 polyprenols affect thylakoid membrane ultra-structure and hence influence photosynthetic apparatus performance in plants such as Arabidopsis and tomato. So far nothing is known about the hormonal or environmental regulation of CPT7 gene expression. The aim of our study was to find out if medium-chain-length polyprenol biosynthesis in plants may be regulated by hormonal cues.We found that the CPT7 gene in Arabidopsis has a BZR1 binding element (brassinosteroid dependent) in its promoter. Brassinosteroid signaling mutants in Arabidopsis accumulate a lower amount of medium-chain-length C45-C55 polyprenols than control plants. At the same time carotenoid and chlorophyll content is increased, and the amount of PsbD1A protein coming from photosystem II does not undergo a significant change. On contrary, treatment of WT plants with epi-brassinolide increases C45-C55 polyprenols content. We also report decreased transcription of MEP enzymes (besides C45-C55 polyprenols, precursors of numerous isoprenoids, e.g. phytol, carotenoids are derived from this pathway) and genes encoding biosynthesis of medium-chain-length polyprenol enzymes in brassinosteroid perception mutant bri1-116. Taken together, we document that brassinosteroids affect biosynthetic pathway of C45-C55 polyprenols.

Comprehensive Analysis of BR Receptor Expression under Hormone Treatment in the Rubber Tree (Hevea brasiliensis Muell. Arg.)

Brassinosteroids (BRs) are important for plant growth and development, with BRI1 and BAK1 kinases playing an important role in BR signal transduction. Latex from rubber trees is crucial for industry, medicine and defense use. Therefore, it is beneficial to characterize and analyze HbBRI1 and HbBAK1 genes to improve the quality of the resources obtained from Hevea brasiliensis (rubber tree). Based on bioinformatics predictions and rubber tree database, five HbBRI1s with four HbBAK1s were identified and named HbBRI1~HbBRL3 and HbBAK1a~HbBAK1d, respectively, which were clustered in two groups. HbBRI1 genes, except for HbBRL3, exclusively contain introns, which is convenient for responding to external factors, whereas HbBAK1b/c/d contain 10 introns and 11 exons, and HbBAK1a contains eight introns. Multiple sequence analysis showed that HbBRI1s include typical domains of the BRI1 kinase, indicating that HbBRI1s belong to BRI1. HbBAK1s that possess LRR and STK_BAK1_like domains illustrate that HbBAK1s belong to the BAK1 kinase. BRI1 and BAK1 play an important role in regulating plant hormone signal transduction. Analysis of the cis-element of all HbBRI1 and HbBAK1 genes identified hormone response, light regulation and abiotic stress elements in the promoters of HbBRI1s and HbBAK1s. The results of tissue expression patterns indicate that HbBRL1/2/3/4 and HbBAK1a/b/c are highly expressed in the flower, especially HbBRL2-1. The expression of HbBRL3 is extremely high in the stem, and the expression of HbBAK1d is extremely high in the root. Expression profiles with different hormones show that HbBRI1 and HbBAK1 genes are extremely induced by different hormone stimulates. These results provide theoretical foundations for further research on the functions of BR receptors, especially in response to hormone signals in the rubber tree.

Modifications of Phytohormone Metabolism Aimed at Stimulation of Plant Growth, Improving Their Productivity and Tolerance to Abiotic and Biotic Stress Factors

Due to the growing human population, the increase in crop yield is an important challenge for modern agriculture. As abiotic and biotic stresses cause severe losses in agriculture, it is also crucial to obtain varieties that are more tolerant to these factors. In the past, traditional breeding methods were used to obtain new varieties displaying demanded traits. Nowadays, genetic engineering is another available tool. An important direction of the research on genetically modified plants concerns the modification of phytohormone metabolism. This review summarizes the state-of-the-art research concerning the modulation of phytohormone content aimed at the stimulation of plant growth and the improvement of stress tolerance. It aims to provide a useful basis for developing new strategies for crop yield improvement by genetic engineering of phytohormone metabolism.

Receptor-like Kinases (LRR-RLKs) in Response of Plants to Biotic and Abiotic Stresses

Plants live under different biotic and abiotic stress conditions, and, to cope with the adversity and severity, plants have well-developed resistance mechanisms. The mechanism starts with perception of the stimuli followed by molecular, biochemical, and physiological adaptive measures. The family of LRR-RLKs (leucine-rich repeat receptor-like kinases) is one such group that perceives biotic and abiotic stimuli and also plays important roles in different biological processes of development. This has been mostly studied in the model plant, Arabidopsis thaliana, and to some extent in other plants, such as Solanum lycopersicum, Nicotiana benthamiana, Brassica napus, Oryza sativa, Triticum aestivum, Hordeum vulgare, Brachypodium distachyon, Medicago truncatula, Gossypium barbadense, Phaseolus vulgaris, Solanum tuberosum, and Malus robusta. Most LRR-RLKs tend to form different combinations of LRR-RLKs-complexes (dimer, trimer, and tetramers), and some of them were observed as important receptors in immune responses, cell death, and plant development processes. However, less is known about the function(s) of LRR-RLKs in response to abiotic and biotic stresses. Here, we give recent updates about LRR-RLK receptors, specifically focusing on their involvement in biotic and abiotic stresses in the model plant, A. thaliana. Furthermore, the recent studies on LRR-RLKs that are homologous in other plants is also reviewed in relation to their role in triggering stress response processes against biotic and abiotic stimuli and/or in exploring their additional function(s). Furthermore, we present the interactions and combinations among LRR-RLK receptors that have been confirmed through experiments. Moreover, based on GENEINVESTIGATOR microarray database analysis, we predict some potential LRR-RLK genes involved in certain biotic and abiotic stresses whose function and mechanism may be explored.

Brassinosteroid Signaling Downstream Suppressor BIN2 Interacts with SLFRIGIDA-LIKE to Induce Early Flowering in Tomato

Brassinosteroid (BR) signaling is very important in plant developmental processes. Its various components interact to form a signaling cascade. These components are widely studied in Arabidopsis; however, very little information is available on tomatoes. Brassinosteroid Insensitive 2 (BIN2), the downstream suppressor of BR signaling, plays a critical role in BR signal pathway, while FRIGIDA as a key suppressor of Flowering Locus C with overexpression could cause early flowering; however, how the BR signaling regulates FRIGIDA homologous protein to adjust flowering time is still unknown. This study identified 12 FRIGIDA-LIKE proteins with a conserved FRIGIDA domain in tomatoes. Yeast two-hybrid and BiFC confirmed that SlBIN2 interacts with 4 SlFRLs, which are sub-cellularly localized in the nucleus. Tissue-specific expression of SlFRLs was observed highly in young roots and flowers. Biological results revealed that SlFRLs interact with SlBIN2 to regulate early flowering. Further, the mRNA level of SlBIN2 also increased in SlFRL-overexpressed lines. The relative expression of SlCPD increased upon SlFRL silencing, while SlDWF and SlBIN2 were decreased, both of which are important for BR signaling. Our research firstly provides molecular evidence that BRs regulate tomato flowering through the interaction between SlFRLs and SlBIN2. This study will promote the understanding of the specific pathway essential for floral regulation.

A mutant allele of the flowering promoting factor 1 gene at the tomato BRACHYTIC locus reduces plant height with high quality fruit

Reduced plant height due to shortened stems is beneficial for improving crop yield potential, better resilience to biotic/abiotic stresses, and rapid crop producer adoption of the agronomic and management practices. Breeding tomato plants with a reduced height, however, poses a particular challenge because this trait is often associated with a significant fruit size (weight) reduction. The tomato BRACHYTIC (BR) locus controls plant height. Genetic mapping and genome assembly revealed three flowering promoting factor 1 (FPF1) genes located within the BR mapping interval, and a complete coding sequence deletion of the telomere proximal FPF1 (Solyc01g066980) was found in the br allele but not in BR. The knock-out of Solyc01g066980 in BR large-fruited fresh-market tomato reduced the height and fruit yield, but the ability to produce large size fruits was retained. However, concurrent yield evaluation of a pair of sister lines with or without the br allele revealed that artificial selection contributes to commercially acceptable yield potential in br tomatoes. A network analysis of gene-expression patterns across genotypes, tissues, and the gibberellic acid (GA) treatment revealed that member(s) of the FPF1 family may play a role in the suppression of the GA biosynthesis in roots and provided a framework for identifying the responsible molecular signaling pathways in br-mediated phenotypic changes. Lastly, mutations of br homologs also resulted in reduced height. These results shed light on the genetic and physiological mechanisms by which the br allele alters tomato architecture.

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.

Enhanced brassinosteroid signaling via the overexpression of SlBRI1 positively regulates the chilling stress tolerance of tomato

Brassinosteroids (BRs) regulate plant development and response to stress. BRASSINOSTEROID INSENSITIVE 1 (BRI1) is a BR receptor that activates BR signaling. Although the function of the tomato BR receptor SlBRI1 in regulating growth and drought resistance has been examined, that of SlBRI1 in cold tolerance is unclear. This study indicated that the expression of SlBRI1 in tomato was rapidly induced and reached its highest level at 3 h under chilling treatment and then decreased. The overexpression of SlBRI1 displayed low relative electrolyte leakage, malondialdehyde content, and reactive oxygen species (ROS) accumulation under chilling stress. The proline content and activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in SlBRI1OE plants were higher than those in the wild-type (WT) plants after chilling stress. The transcript abundances of five cold-responsive genes were higher in SlBRI1OE plants than in WT plants during chilling stress. RNA sequence analysis showed that the expression of the majority of genes encoding photosystem I and II were downregulated. The degree of suppression in SlBRI1OE plants was weaker than that in WT plants. Additionally, the Pn and Fv/Fm of SlBRI1OE plants were significantly higher than those of WT plants under chilling stress. We identified several genes encoding key enzymes in BRs; indole acetic acid (IAA), gibberellin (GA), and abscisic acid (ABA) biosynthesis or signaling were upregulated or downregulated during chilling stress. Chilling stress decreased the BRs and GA3 content, and increased IAA and ABA content. The contents were lower or higher in SlBRI1OE than in WT plants. Furthermore, chilling stress regulated the expression levels of 43 transcription factors. The expression of seven cold-regulated protein genes was higher or lower in SlBRI1OE plants than in WT plants under chilling stress. These results suggest that SlBRI1 positively regulates chilling tolerance mainly through ICE1-CBF-COR pathway in tomato.

Transcriptome Profiling and Identification of the Candidate Genes Involved in Early Ripening in Ziziphus Jujuba

The early ripening jujube is an immensely popular fresh fruit due to its high commercial value as well as rich nutrition. However, little is known about the mechanism of jujube fruit’s ripening. In this study, the transcriptome profiles were comprehensively analyzed between the ‘Lingwu Changzao’ jujube and its early-ripening mutant during the fruit development and maturity. A total of 5,376 and 762 differentially expressed genes (DEGs) were presented at 80 and 90 days after the flowering of the jujube fruit, respectively. Furthermore, 521 common DEGs were identified as candidate genes that might be associated with the fruit’s early ripening. Our findings demonstrated that in a non-climacteric jujube fruit, abscisic acid (ABA) was more greatly involved in fruit ripening than ethylene. Meanwhile, the fruit ripening of the early-ripening mutant was regulated by eight promotors of DEGs related to glucose and fructose, seven repressors of DEGs related to brassinosteroid signal transduction, and a series of transcription factor genes (MYB, Bhlh, and ERF). Additionally, the expression of 20 candidate DEGs was further validated by real-time PCR during the late fruit maturation stage. Collectively, the present study sheds light on the metabolic mechanism of the fruit’s early ripening and provides valuable candidate genes for the early-ripening mutant’s breeding.

Over-expression of TaDWF4 increases wheat productivity under low and sufficient nitrogen through enhanced carbon assimilation

There is a strong pressure to reduce nitrogen (N) fertilizer inputs while maintaining or increasing current cereal crop yields. We show that overexpression of TaDWF4-B, the dominant shoot expressed homoeologue of OsDWF4, in wheat can increase plant productivity by up to 105% under a range of N levels on marginal soils, resulting in increased N use efficiency (NUE). We show that a two to four-fold increase in TaDWF4 transcript levels enhances the responsiveness of genes regulated by N. The productivity increases seen were primarily due to the maintenance of photosystem II operating efficiency and carbon assimilation in plants when grown under limiting N conditions and not an overall increase in photosynthesis capacity. The increased biomass production and yield per plant in TaDWF4 OE lines could be linked to modified carbon partitioning and changes in expression pattern of the growth regulator Target Of Rapamycin, offering a route towards breeding for sustained yield and lower N inputs.

In wheat, overexpression of TaDWF4 overrides normal nutrient sensing allowing for increased biomass when grown under limiting nutrient conditions. This maintenance of growth is associated with modified carbon partitioning and changes in expression of growth regulator TaTOR, offering a route towards breeding for sustained yields with lower nitrogen inputs.

Inhibition of 4-HYDROXYPHENYLPYRUVATE DIOXYGENASE expression by brassinosteroid reduces carotenoid accumulation in Arabidopsis

Unlike the indispensable function of the steroid hormone brassinosteroid (BR) in regulating plant growth and development, the metabolism of secondary metabolites regulated by BR is not well known. Here we show that BR reduces carotenoid accumulation in Arabidopsis seedlings. BR-deficient or BR-insensitive mutants accumulated higher content of carotenoids than wild-type plants, whereas BR treatment reduced carotenoid content. We demonstrated that BR transcriptionally suppresses 4-HYDROXYPHENYLPYRUVATE DIOXYGENASE (HPPD) expression involved in carotenogenesis via plastoquinone production. We found that the expression of HPPD displays an oscillation pattern that is expressed more strongly in dark than in light conditions. Moreover, BR appeared to inhibit HPPD expression more strongly in darkness than in light, leading to suppression of a diurnal oscillation of HPPD expression. BR-responsive transcription factor BRASSINAZOLE RESISTANT 1 (BZR1) directly bound to the promoter of HPPD, and HPPD suppression by BR was increased in the bzr1-1D gain-of-function mutation. Interestingly, dark-induced HPPD expression did not cause carotenoid accumulation, due to down-regulation of other carotenoid biosynthetic genes in the dark. Our results suggest that BR regulates different physiological responses in dark and light through inhibition of HPPD expression.

Brassinosteroids and metalloids: Regulation of plant biology

Metalloid contamination in the environment is one of the serious concerns posing threat to our ecosystems. Excess of metalloid concentrations (including antimony, arsenic, boron, selenium etc.) in soil results in their over accumulation in plant tissues, which ultimately causes phytotoxicity and their bio-magnification. So, it is very important to find some ecofriendly approaches to counter negative impacts of above mentioned metalloids on plant system. Brassinosteroids (BRs) belong to family of plant steroidal hormones, and are considered as one of the ecofriendly way to counter metalloid phytotoxicity. This phytohormone regulates the plant biology in presence of metalloids by modulating various key biological processes like cell signaling, primary and secondary metabolism, bio-molecule crosstalk and redox homeostasis. The present review explains the in-depth mechanisms of BR regulated plant responses in presence of metalloids, and provides some biotechnological aspects towards ecofriendly management of metalloid contamination.

Transcriptomic analysis unravels the molecular response of Lonicera japonica leaves to chilling stress

Lonicera japonica is not only an important resource of traditional Chinese medicine, but also has very high horticultural value. Studies have been performed on the physiological responses of L. japonica leaves to chilling, however, the molecular mechanism underlying the low temperature-induced leaves morphological changes remains unclear. In this study, it has been demonstrated that the ratio of pigments content including anthocyanins, chlorophylls, and carotenoids was significantly altered in response to chilling condition, resulting in the color transformation of leaves from green to purple. Transcriptomic analysis showed there were 10,329 differentially expressed genes (DEGs) co-expressed during chilling stress. DEGs were mainly mapped to secondary metabolism, cell wall, and minor carbohydrate. The upregulated genes (UGs) were mainly enriched in protein metabolism, transport, and signaling, while UGs in secondary metabolism were mainly involved in phenylpropaoids-flavonoids pathway (PFP) and carotenoids pathway (CP). Protein-protein interaction analysis illustrated that 21 interacted genes including CAX3, NHX2, ACA8, and ACA9 were enriched in calcium transport/potassium ion transport. BR biosynthesis pathway related genes and BR insensitive (BRI) were collectively induced by chilling stress. Furthermore, the expression of genes involved in anthocyanins and CPs as well as the content of chlorogenic acid (CGA) and luteoloside were increased in leaves of L. japonica under stress. Taken together, these results indicate that the activation of PFP and CP in leaves of L. japonica under chilling stress, largely attributed to the elevation of calcium homeostasis and stimulation of BR signaling, which then regulated the PFP/CP related transcription factors.

Insight into Details of the Photosynthetic Light Reactions and Selected Metabolic Changes in Tomato Seedlings Growing under Various Light Spectra

The objective of our study was to characterise the growth of tomato seedlings under various light spectra, but special attention has been paid to gaining a deeper insight into the details of photosynthetic light reactions. The following light combinations (generated by LEDs, constant light intensity at 300 μmol m⁻² s⁻¹) were used: blue/red light; blue/red light + far red; blue/red light + UV; white light that was supplemented with green, and white light that was supplemented with blue. Moreover, two combinations of white light for which the light intensity was changed by imitating the sunrise, sunset, and moon were also tested. The reference point was also light generated by high pressure sodium lamps (HPS). Plant growth/morphological parameters under various light conditions were only partly correlated with the photosynthetic efficiency of PSI and PSII. Illumination with blue/red as the main components had a negative effect on the functioning of PSII compared to the white light and HPS-generated light. On the other hand, the functioning of PSI was especially negatively affected under the blue/red light that was supplemented with FR. The FT-Raman studies showed that the general metabolic profile of the leaves (especially proteins and β-carotene) was similar in the plants that were grown under the HPS and under the LED-generated white light for which the light intensity changed during a day. The effect of various light conditions on the leaf hormonal balance (auxins, brassinosteroids) is also discussed.

PtBRI1.2 promotes shoot growth and wood formation through a brassinosteroid-mediated PtBZR1-PtWNDs module in poplar

Brassinosteroid-insensitive-1 (BRI1) plays important roles in various signalling pathways controlling plant growth and development. However, the regulatory mechanism of BRI1 in brassinosteroid (BR)-mediated signalling for shoot growth and wood formation in woody plants is largely unknown. In this study, PtBRI1.2, a brassinosteroid-insensitive-1 gene, was overexpressed in poplar. Shoot growth and wood formation of transgenic plants were examined and the regulatory genes involved were verified. PtBRI1.2 was localized to the plasma membrane, with a predominant expression in leaves. Ectopic expression of PtBRI1.2 in Arabidopsis bri1-201 and bri1-5 mutants rescued their retarded-growth phenotype. Overexpression of PtBRI1.2 in poplar promoted shoot growth and wood formation in transgenic plants. Further studies revealed that overexpression of PtBRI1.2 promoted the accumulation of PtBZR1 (BRASSINAZOLE RESISTANT1) in the nucleus, which subsequently activated PtWNDs (WOOD-ASSOCIATED NAC DOMAIN transcription factors) to up-regulate expression of secondary cell wall biosynthesis genes involved in wood formation. Our results suggest that PtBRI1.2 plays a crucial role in regulating shoot growth and wood formation by activating BR signalling.

Modification of Threonine-825 of SlBRI1 Enlarges Cell Size to Enhance Fruit Yield by Regulating the Cooperation of BR-GA Signaling in Tomato

Brassinosteroids (BRs) are growth-promoting phytohormones that can efficiently function by exogenous application at micromolar concentrations or by endogenous fine-tuning of BR-related gene expression, thus, precisely controlling BR signal strength is a key factor in exploring the agricultural potential of BRs. BRASSINOSTEROID INSENSITIVE1 (BRI1), a BR receptor, is the rate-limiting enzyme in BR signal transduction, and the phosphorylation of each phosphorylation site of SlBRI1 has a distinct effect on BR signal strength and botanic characteristics. We recently demonstrated that modifying the phosphorylation sites of tomato SlBRI1 could improve the agronomic traits of tomato to different extents; however, the associated agronomic potential of SlBRI1 phosphorylation sites in tomato has not been fully exploited. In this research, the biological functions of the phosphorylation site threonine-825 (Thr-825) of SlBRI1 in tomato were investigated. Phenotypic analysis showed that, compared with a tomato line harboring SlBRI1, transgenic tomato lines expressing SlBRI1 with a nonphosphorylated Thr-825 (T825A) exhibited a larger plant size due to a larger cell size and higher yield, including a greater plant height, thicker stems, longer internodal lengths, greater plant expansion, a heavier fruit weight, and larger fruits. Molecular analyses further indicated that the autophosphorylation level of SlBRI1, BR signaling, and gibberellic acid (GA) signaling were elevated when SlBRI1 was dephosphorylated at Thr-825. Taken together, the results demonstrated that dephosphorylation of Thr-825 can enhance the functions of SlBRI1 in BR signaling, which subsequently activates and cooperates with GA signaling to stimulate cell elongation and then leads to larger plants and higher yields per plant. These results also highlight the agricultural potential of SlBRI1 phosphorylation sites for breeding high-yielding tomato varieties through precise control of BR signaling.

EjBZR1 represses fruit enlargement by binding to the EjCYP90 promoter in loquat

Loquat (Eriobotrya japonica) is a subtropical tree that bears fruit that ripens during late spring. Fruit size is one of the dominant factors inhibiting the large-scale production of this fruit crop. To date, little is known about fruit size regulation. In this study, we first discovered that cell size is more important to fruit size than cell number in loquat and that the expression of the EjBZR1 gene is negatively correlated with cell and fruit size. Virus-induced gene silencing (VIGS) of EjBZR1 led to larger cells and fruits in loquat, while its overexpression reduced cell and plant size in Arabidopsis. Moreover, both the suppression and overexpression of EjBZR1 inhibited the expression of brassinosteroid (BR) biosynthesis genes, especially that of EjCYP90A. Further experiments indicated that EjCYP90A, a cytochrome P450 gene, is a fruit growth activator, while EjBZR1 binds to the BRRE (CGTGTG) motif of the EjCYP90A promoter to repress its expression and fruit cell enlargement. Overall, our results demonstrate a possible pathway by which EjBZR1 directly targets EjCYP90A and thereby affects BR biosynthesis, which influences cell expansion and, consequently, fruit size. These findings help to elucidate the molecular functions of BZR1 in fruit growth and thus highlight a useful genetic improvement that can lead to increased crop yields by repressing gene expression.

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.

Brassinosteroid Signaling, Crosstalk and, Physiological Functions in Plants Under Heavy Metal Stress

Brassinosteroids (BRs) are group of plant steroidal hormones that modulate developmental processes and also have pivotal role in stress management. Biosynthesis of BRs takes place through established early C-6 and late C-6 oxidation pathways and the C-22 hydroxylation pathway triggered by activation of the DWF4 gene that acts on multiple intermediates. BRs are recognized at the cell surface by the receptor kinases, BRI1 and BAK1, which relay signals to the nucleus through a phosphorylation cascade involving phosphorylation of BSU1 protein and proteasomal degradation of BIN2 proteins. Inactivation of BIN2 allows BES1/BZR1 to enter the nucleus and regulate the expression of target genes. In the whole cascade of signal recognition, transduction and regulation of target genes, BRs crosstalk with other phytohormones that play significant roles. In the current era, plants are continuously exposed to abiotic stresses and heavy metal stress is one of the major stresses. The present study reveals the mechanism of these events from biosynthesis, transport and crosstalk through receptor kinases and transcriptional networks under heavy metal stress.

The conserved brassinosteroid-related transcription factor BIM1a negatively regulates fruit growth in tomato

Brassinosteroids (BRs) are steroid hormones that play key roles in plant development and defense. Our goal is to harness the extensive knowledge of the Arabidopsis BR signaling network to improve productivity in crop species. This first requires identifying components of the conserved network and their function in the target species. Here, we investigated the function of SlBIM1a, the closest tomato homolog of AtBIM1, which is highly expressed in fruit. SlBIM1a-overexpressing lines displayed severe plant and fruit dwarfism, and histological characterization of different transgenic lines revealed that SlBIM1a expression negatively correlated with fruit pericarp cell size, resulting in fruit size modifications. These growth phenotypes were in contrast to those found in Arabidopsis, and this was confirmed by the reciprocal ectopic expression of SlBIM1a/b in Arabidopsis and of AtBIM1 in tomato. These results determined that BIM1 function depends more on the recipient species than on its primary sequence. Yeast two-hybrid interaction studies and transcriptomic analyses of SlBIM1a-overexpressing fruit further suggested that SlBIM1a acts through its interaction with SlBZH1 to govern the transcriptional regulation of growth-related BR target genes. Together, these results suggest that SlBIM1a is a negative regulator of pericarp cell expansion, possibly at the crossroads with auxin and light signaling.

Molecular Dynamics of Chloroplast Membranes Isolated from Wild-Type Barley and a Brassinosteroid-Deficient Mutant Acclimated to Low and High Temperatures

Plants have developed various acclimation strategies in order to counteract the negative effects of abiotic stresses (including temperature stress), and biological membranes are important elements in these strategies. Brassinosteroids (BR) are plant steroid hormones that regulate plant growth and development and modulate their reaction against many environmental stresses including temperature stress, but their role in modifying the properties of the biological membrane is poorly known. In this paper, we characterise the molecular dynamics of chloroplast membranes that had been isolated from wild-type and a BR-deficient barley mutant that had been acclimated to low and high temperatures in order to enrich the knowledge about the role of BR as regulators of the dynamics of the photosynthetic membranes. The molecular dynamics of the membranes was investigated using electron paramagnetic resonance (EPR) spectroscopy in both a hydrophilic and hydrophobic area of the membranes. The content of BR was determined, and other important membrane components that affect their molecular dynamics such as chlorophylls, carotenoids and fatty acids in these membranes were also determined. The chloroplast membranes of the BR-mutant had a higher degree of rigidification than the membranes of the wild type. In the hydrophilic area, the most visible differences were observed in plants that had been grown at 20 °C, whereas in the hydrophobic core, they were visible at both 20 and 5 °C. There were no differences in the molecular dynamics of the studied membranes in the chloroplast membranes that had been isolated from plants that had been grown at 27 °C. The role of BR in regulating the molecular dynamics of the photosynthetic membranes will be discussed against the background of an analysis of the photosynthetic pigments and fatty acid composition in the chloroplasts.

Genome-Wide Identification and Molecular Characterization of the Growth-Regulating Factors-Interacting Factor Gene Family in Tomato

Growth-regulating factors-interacting factor (GIF) proteins play crucial roles in the regulation of plant growth and development. However, the molecular mechanism of GIF proteins in tomato is poorly understood. Here, four SlGIF genes (named SlGRF1a, SlGIF1b, SlGIF2, and SlGIF3) were identified from the tomato genome and clustered into two major clades by phylogenetic analysis. The gene structure and motif pattern analyses showed similar exon/intron patterns and motif organizations in all the SlGIFs. We identified 33 cis-acting regulatory elements (CAREs) in the promoter regions of the SlGIFs. The expression profiling revealed the four GIFs are expressed in various tissues and stages of fruit development and induced by phytohormones (IAA and GA). The subcellular localization assays showed all four GIFs were located in nucleus. The yeast two-hybrid assay indicated various growth-regulating factors (SlGRFs) proteins interacted with the four SlGIF proteins. However, SlGRF4 was a common interactor with the SlGIF proteins. Moreover, a higher co-expression relationship was shown between three SlGIF genes and five SlGRF genes. The protein association network analysis found a chromodomain helicase DNA-binding protein (CHD) and an actin-like protein to be associated with the four SlGIF proteins. Overall, these results will improve our understanding of the potential functions of GIF genes and act as a base for further functional studies on GIFs in tomato growth and development.

Brassinosteroid Regulates 3-Hydroxy-3-methylglutaryl CoA Reductase to Promote Grape Fruit Development

Brassinosteroids (BRs) are known to regulate plant growth and development. However, only little is known about their mechanism in the regulation of berry development in grapes. This study demonstrates that BR treatment enhances the accumulation of fruit sugar components, reduces the content of organic acids (e.g., tartaric acid), promotes coloration, and increases the anthocyanin content in grape berries at the onset of the veraison, half veraison, and full veraison stages at the rate of 0.0998, 0.0560, and 0.0281 mg·g^-1_, respectively. In addition, BR treatment was also found to accelerate the biosynthesis of terpenoid aroma components, such as α-pinene, d-limonene, and γ-terpinene, which influence the aromatic composition of grapes. BRs can negatively regulate the expression of VvHMGR, a key gene involved in the mevalonate (MVA) pathway, and reduce the activity of 3-hydroxy-3-methylglutaryl CoA reductase (HMGR). Inhibiting the expression of HMGR promoted the accumulation of anthocyanins and fruit coloration. Meanwhile, after the inhibition, the contents of auxin indole-3-acetic acid (IAA), abscisic acid (ABA), and brassinosteroid (BR) increased, while gibberellin (GA₃) and zeatin riboside (ZR) decreased, and its aromatic composition also changed. Therefore, it may be concluded that BRs inhibited HMGR activity and cooperated with VvHMGR to regulate the formation of color, aroma, and other quality characteristics in fruits.

Modification of Serine 1040 of SIBRI1 Increases Fruit Yield by Enhancing Tolerance to Heat Stress in Tomato

High temperature is a major environmental factor that adversely affects plant growth and production. SlBRI1 is a critical receptor in brassinosteroid signalling, and its phosphorylation sites have differential functions in plant growth and development. However, the roles of the phosphorylation sites of SIBRI1 in stress tolerance are unknown. In this study, we investigated the biological functions of the phosphorylation site serine 1040 (Ser-1040) of SlBRI1 in tomato. Phenotype analysis indicated that transgenic tomato harbouring SlBRI1 dephosphorylated at Ser-1040 showed increased tolerance to heat stress, exhibiting better plant growth and plant yield under high temperature than transgenic lines expressing SlBRI1 or SlBRI1 phosphorylated at Ser-1040. Biochemical and physiological analyses further showed that antioxidant activity, cell membrane integrity, osmo-protectant accumulation, photosynthesis and transcript levels of heat stress defence genes were all elevated in tomato plants harbouring SlBRI1 dephosphorylated at Ser-1040, and the autophosphorylation level of SlBRI1 was inhibited when SlBRI1 dephosphorylated at Ser-1040. Taken together, our results demonstrate that the phosphorylation site Ser-1040 of SlBRI1 affects heat tolerance, leading to improved plant growth and yield under high-temperature conditions. Our results also indicate the promise of phosphorylation site modification as an approach for protecting crop yields from high-temperature stress.

Gaining Insight into Exclusive and Common Transcriptomic Features Linked to Drought and Salinity Responses across Fruit Tree Crops

The present study aimed at identifying and mapping key genes expressed in root tissues involved in drought and salinity tolerance/resistance conserved among different fruit tree species. Twenty-six RNA-Seq samples were analyzed from six published studies in five plant species (Olea europaea, Vitis riparia Michx, Prunus mahaleb, Prunus persica, Phoenix dactylifera). This meta-analysis used a bioinformatic pipeline identifying 750 genes that were commonly modulated in three salinity studies and 683 genes that were commonly regulated among three drought studies, implying their conserved role in resistance/tolerance/response to these environmental stresses. A comparison was done on the genes that were in common among both salinity and drought resulted in 82 genes, of which 39 were commonly regulated with the same trend of expression (23 were upregulated and 16 were downregulated). Gene set enrichment and pathway analysis pointed out that pathways encoding regulation of defense response, drug transmembrane transport, and metal ion binding are general key molecular responses to these two abiotic stress responses. Furthermore, hormonal molecular crosstalk plays an essential role in the fine-tuning of plant responses to drought and salinity. Drought and salinity induced a different molecular "hormonal fingerprint". Dehydration stress specifically enhanced multiple genes responsive to abscisic acid, gibberellin, brassinosteroids, and the ethylene-activated signaling pathway. Salt stress mostly repressed genes encoding for key enzymes in signaling proteins in auxin-, gibberellin-(gibberellin 2 oxidase 8), and abscisic acid-related pathways (aldehyde oxidase 4, abscisic acid-responsive element-binding protein 3). Abiotic stress-related genes were mapped into the chromosome to identify molecular markers usable for the improvement of these complex quantitative traits. This meta-analysis identified genes that serve as potential targets to develop cultivars with enhanced drought and salinity resistance and/or tolerance across different fruit tree crops in a biotechnological sustainable way.

Map-based cloning of qBWT-c12 discovered brassinosteroid-mediated control of organ size in cotton

Assuring fiber yield stability is the primary objective for cotton breeders since the world population is on the rise, and the demand for cotton fiber is increasing every year. Thus, enhancing average cotton boll weight (BWT) could improve seed cotton production, and ultimately to increase cotton fiber yield. This study accomplished the map-based cloning of a novel boll weight regulating locus, qBWT-c12, in cotton. Bulk segregation analysis detected linked markers, aided in the detection of a stable BWT regulating locus, qBWT-c12, on Chr12 in a novel boll size mutant, BS41. Progeny evaluation confined the qBWT-c12 to a 0.89 cM interval between the AD-A12_07 and AD-FM_44 markers in recombinant derived F₃ and F₄ populations. Homology mapping detected a 40 bp insertion-deletion (InDel) site in the AD-FM_44 clone sequence situated +341 downstream of GhBRH1_A12, which showed complete linkage to the BWT phenotype. The suppressed expression of GhBRH1_A12 suggested its putative involvement during early boll development events in BS41. Although brassinosteroid (BR) biosynthesis and signaling pathway genes were up regulated in different tissues, but the organ growth was suppressed leading to dwarf plants, smaller leaves, and de-morphed smaller bolls in BS41. Thus, a disruption in the BR signal cascade is anticipated and could be related to lower GhBRH1_A12 expression in BS41.This study firstly reported the genetic dissection of boll size regulation of G. barbadense in G. hirsutum background using map-based cloning of a BWT regulating locus, qBWT-c12. Moreover, it also emphasized the putative role GhBRH1_A12 in regulating BR homeostasis and its potential to modulate plant growth and boll development in cotton.

Transcriptional Differences in Peanut (Arachis hypogaea L.) Seeds at the Freshly Harvested, After-ripening and Newly Germinated Seed Stages: Insights into the Regulatory Networks of Seed Dormancy Release and Germination

Seed dormancy and germination are the two important traits related to plant survival, reproduction and crop yield. To understand the regulatory mechanisms of these traits, it is crucial to clarify which genes or pathways participate in the regulation of these processes. However, little information is available on seed dormancy and germination in peanut. In this study, seeds of the variety Luhua No.14, which undergoes nondeep dormancy, were selected, and their transcriptional changes at three different developmental stages, the freshly harvested seed (FS), the after-ripening seed (DS) and the newly germinated seed (GS) stages, were investigated by comparative transcriptomic analysis. The results showed that genes with increased transcription in the DS vs FS comparison were overrepresented for oxidative phosphorylation, the glycolysis pathway and the tricarboxylic acid (TCA) cycle, suggesting that after a period of dry storage, the intermediates stored in the dry seeds were rapidly mobilized by glycolysis, the TCA cycle, the glyoxylate cycle, etc.; the electron transport chain accompanied by respiration was reactivated to provide ATP for the mobilization of other reserves and for seed germination. In the GS vs DS pairwise comparison, dozens of the upregulated genes were related to plant hormone biosynthesis and signal transduction, including the majority of components involved in the auxin signal pathway, brassinosteroid biosynthesis and signal transduction as well as some GA and ABA signal transduction genes. During seed germination, the expression of some EXPANSIN and XYLOGLUCAN ENDOTRANSGLYCOSYLASE genes was also significantly enhanced. To investigate the effects of different hormones during seed germination, the contents and differential distribution of ABA, GAs, BRs and IAA in the cotyledons, hypocotyls and radicles, and plumules of three seed sections at different developmental stages were also investigated. Combined with previous data in other species, it was suggested that the coordination of multiple hormone signal transduction nets plays a key role in radicle protrusion and seed germination.

Regulation of sterol content and biosynthetic gene expression during flower opening and early fruit development in olive

Phytosterols are lipophilic membrane components essential not only for diverse cellular functions but also are biosynthetic precursors of the plant hormone, brassinosteroid (BR). However, the interaction between phytosterol and BR during early fleshy-fruit growth remains largely uncharacterized. In olive, phytosterols are important lipids because they affect oil quality, but phytosterol composition during flowering and early fruit development has not been explored. Here, we first investigated the temporal changes in phytosterol composition, and biosynthetic gene expression that occurred during olive flower opening and early fruit growth. Next, we analyzed the interrelationship between phytosterol and BR, whose levels we manipulated through the application of exogenous BRs (24-epibrassinolide, EBR) or a BR biosynthesis inhibitor (brassinazole, Brz). In this report, the profiling of phytosterol measurement revealed that β-sitosterol is the most abundant in olive reproductive organs. Our data demonstrate that both OeCYP51 and OeSMT2 genes are upregulated during floral anthesis in good agreement with the rise in cholesterol and β-sitosterol contents in olive flower. By contrast, the OeCYP51 and OeSMT2 genes displayed different expression patterns during early olive-fruit development. Furthermore, our data show that exogenous EBR enhanced the early olive-fruit growth, as well as the OeSMT2 transcript and β-sitosterol levels, but decreased the OeCYP51 transcript, squalene, campesterol and cholesterol levels, whereas the Brz treatment exerted the opposite effect. Overall, our findings indicate an up-regulation of β-sitosterol biosynthesis by BR at the transcriptional level during early olive-fruit growth, providing a valuable tool to unravel the physiological function of SMT2 in future studies.

Modification of Threonine-1050 of SlBRI1 regulates BR Signalling and increases fruit yield of tomato

BACKGROUND

Appropriate brassinosteroid (BR) signal strength caused by exogenous application or endogenous regulation of BR-related genes can increase crop yield. However, precise control of BR signals is difficult and can cause unstable effects and failure to reach full potential. Phosphorylated BRASSINOSTEROID INSENSITIVE1 (BRI1), the rate-limiting receptor in BR signalling, transduces BR signals, and we recently demonstrated that modifying BRI1 phosphorylation sites alters BR signal strength and botanical characteristics in Arabidopsis. However, the functions of such phosphorylation sites in agronomic characteristics of crops remain unclear.

RESULTS

In this work, we investigated the roles of tomato SlBRI1 threonine-1050 (Thr-1050). SlBRI1 mutant cu3^-abs1 plants expressing SlBRI1 with a non-phosphorylatable Thr-1050 (T1050A), with a wild-type SlBRI1 transformant used as a control, were examined. The results showed enhanced autophosphorylation of SlBRI1 and BR signal strength for cu3^-abs1 harbouring T1050A, which promoted yield through increased plant expansion, leaf area, fruit weight and fruit number per cluster but reduced nutrient contents, including ascorbic acid and soluble sugar levels. Moreover, plant height, stem diameter, and internodal distance were similar between the transgenic plants.

CONCLUSION

Our results reveal the biological role of Thr-1050 in tomato and provide a molecular basis for establishing high-yield crops by precisely controlling BR signal strength via phosphorylation site modification.

Integrated microRNA and transcriptome profiling reveals a miRNA-mediated regulatory network of embryo abortion under calcium deficiency in peanut (Arachis hypogaea L.)

Background

Peanut embryo development is a complex process involving a series of gene regulatory pathways and is easily affected by various elements in the soil. Calcium deficiency in the soil induces early embryo abortion in peanut, which provides an opportunity to determine the mechanism underlying this important event. MicroRNA (miRNA)-guided target gene regulation is vital to a wide variety of biological processes. However, whether miRNAs participate in peanut embryo abortion under calcium deficiency has yet to be explored.

Results

In this study, with the assistance of a recently established platform for genome sequences of wild peanut species, we analyzed small RNAs (sRNAs) in early peanut embryos. A total of 29 known and 132 potential novel miRNAs were discovered in 12 peanut-specific miRNA families. Among the identified miRNAs, 87 were differentially expressed during early embryo development under calcium deficiency and sufficiency conditions, and 117 target genes of the differentially expressed miRNAs were identified. Integrated analysis of miRNAs and transcriptome expression revealed 52 differentially expressed target genes of 20 miRNAs. The expression profiles for some differentially expressed targets by gene chip analysis were consistent with the transcriptome sequencing results. Together, our results demonstrate that seed/embryo development-related genes such as TCP3, AP2, EMB2750, and GRFs; cell division and proliferation-related genes such as HsfB4 and DIVARICATA; plant hormone signaling pathway-related genes such as CYP707A1 and CYP707A3, with which abscisic acid (ABA) is involved; and BR1, with which brassinosteroids (BRs) are involved, were actively modulated by miRNAs during early embryo development.

Conclusions

Both a number of miRNAs and corresponding target genes likely playing key roles in the regulation of peanut embryo abortion under calcium deficiency were identified. These findings provide for the first time new insights into miRNA-mediated regulatory pathways involved in peanut embryo abortion under calcium deficiency.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5770-6) contains supplementary material, which is available to authorized users.

Enhanced brassinosteroid signaling intensity via SlBRI1 overexpression negatively regulates drought resistance in a manner opposite of that via exogenous BR application in tomato

Brassinosteroids (BRs) regulate plant growth and stress responses. BRASSINOSTEROID-INSENSITIVE 1 (BRI1) is a BR receptor that perceives BRs and subsequently activates BR signaling. However, how BR contents and BRI1 expression levels affect the drought resistance of tomato requires further investigation. Here, we exogenously applied 24-epibrassinolide (EBR) and brassinazole (Brz) to tomato plants and generated different transgenic tomato SlBRI1 overexpression lines to study the drought stress response. Our results showed that EBR application 3 days before drought stress increased the contents of BRs and decreased abscisic acid (ABA) and reactive oxygen species (ROS), after which stomatal aperture and drought resistance eventually increased. Brz application reduced the drought resistance. Astonishingly, overexpression of 35S:SlBRI1, which increased BR signaling intensity, led to slightly improved contents of ABA and ROS and ultimately reduced both stomatal aperture and drought resistance. Moreover, plants expressing SlBRI1 driven by a stress-inducible promoter (Atrd29A) also exhibited reduced plant drought resistance. In all cases, enhancing the BR signaling intensity reduced antioxidant enzyme activity and reduced the expression of drought stress-related genes, ultimately compromising the drought resistance. Additionally, SlBRI1 mutants with altered brassinolide sensitivity (abs), which was weak BR signaling, exhibited significantly increased drought resistance. Therefore, our results reveal that BR contents positively regulated tomato drought resistance and that BR signaling intensity via BRI1 was negatively related to the drought resistance. These imply that the increased drought resistance in response to BRs is a newly discovered BR signaling branch that is located downstream of BRs and that differs from that of BRI1.

Brassinosteroids facilitate xylem differentiation and wood formation in tomato

BR signaling pathways facilitate xylem differentiation and wood formation by fine tuning SlBZR1/SlBZR2-mediated gene expression networks involved in plant secondary growth. Brassinosteroid (BR) signaling and BR crosstalk with diverse signaling cues are involved in the pleiotropic regulation of plant growth and development. Recent studies reported the critical roles of BR biosynthesis and signaling in vascular bundle development and plant secondary growth; however, the molecular bases of these roles are unclear. Here, we performed comparative physiological and anatomical analyses of shoot morphological growth in a cultivated wild-type tomato (Solanum lycopersicum cv. BGA) and a BR biosynthetic mutant [Micro Tom (MT)]. We observed that the canonical BR signaling pathway was essential for xylem differentiation and sequential wood formation by facilitating plant secondary growth. The gradual retardation of xylem development phenotypes during shoot vegetative growth in the BR-deficient MT tomato mutant recovered completely in response to exogenous BR treatment or genetic complementation of the BR biosynthetic DWARF (D) gene. By contrast, overexpression of the tomato Glycogen synthase kinase 3 (SlGSK3) or CRISPR-Cas9 (CR)-mediated knockout of the tomato Brassinosteroid-insensitive 1 (SlBRI1) impaired BR signaling and resulted in severely defective xylem differentiation and secondary growth. Genetic modulation of the transcriptional activity of the tomato Brassinazole-resistant 1/2 (SlBZR1/SlBZR2) confirmed the positive roles of BR signaling pathways for xylem differentiation and secondary growth. Our data indicate that BR signaling pathways directly promote xylem differentiation and wood formation by canonical BR-activated SlBZR1/SlBZR2.

MaBZR1/2 act as transcriptional repressors of ethylene biosynthetic genes in banana fruit

Banana fruit (Musa acuminate L.) ripening is a complex genetical process affected by multiple phytohormones and expression of various genes. However, whether plant hormone brassinosteroid (BR) is involved in this process remains obscure. In this work, three genes that encode BR core signaling components brassinazole resistant (BZR) proteins, namely MaBZR1 to MaBZR3, were characterized from banana fruit. MaBZR1-MaBZR3 exhibited both nuclear and cytoplasmic localization and behaved as transcription inhibitors. Expression analysis showed that MaBZR1/2/3 were continuously decreased as fruit ripening proceeded, indicating their negative roles in banana ripening. Moreover, gel shift and transient expression assays demonstrated that MaBZR1/2 could suppress the transcription of ethylene biosynthetic genes, including MaACS1, MaACO13 and MaACO14, which increased gradually during the banana ripening, via specifically binding to CGTGT/CG sequence in their promoters. Importantly, exogenous application of BRs promotes banana ripening, which is presumably due to the accelerated expression of MaACS1 and MaACO13/14, and consequently the ethylene production. Our study indicates that MaBZR1/2 act as transcriptional repressors of ethylene biosynthetic genes during banana fruit ripening.

Brassinosteroids, the Sixth Class of Phytohormones: A Molecular View from the Discovery to Hormonal Interactions in Plant Development and Stress Adaptation

Phytohormones are natural chemical messengers that play critical roles in the regulation of plant growth and development as well as responses to biotic and abiotic stress factors, maintaining plant homeostasis, and allowing adaptation to environmental changes. The discovery of a new class of phytohormones, the brassinosteroids (BRs), almost 40 years ago opened a new era for the studies of plant growth and development and introduced new perspectives in the regulation of agronomic traits through their use in agriculture. BRs are a group of hormones with significant growth regulatory activity that act independently and in conjunction with other phytohormones to control different BR-regulated activities. Genetic and molecular research has increased our understanding of how BRs and their cross-talk with other phytohormones control several physiological and developmental processes. The present article provides an overview of BRs' discovery as well as recent findings on their interactions with other phytohormones at the transcriptional and post-transcriptional levels, in addition to clarifying how their network works to modulate plant growth, development, and responses to biotic and abiotic stresses.

Expression of a Chloroplast-Targeted Cyanobacterial Flavodoxin in Tomato Plants Increases Harvest Index by Altering Plant Size and Productivity

Tomato is the most important horticultural crop worldwide. Domestication has led to the selection of highly fruited genotypes, and the harvest index (HI), defined as the ratio of fruit yield over total plant biomass, is usually employed as a biomarker of agronomic value. Improvement of HI might then result from increased fruit production and/or lower vegetative growth. Reduction in vegetative biomass has been accomplished in various plant species by expression of flavodoxin, an electron shuttle flavoprotein that interacts with redox-based pathways of chloroplasts including photosynthesis. However, the effect of this genetic intervention on the development of reproductive organs has not been investigated. We show herein that expression of a plastid-targeted cyanobacterial flavodoxin in tomato resulted in significant reduction of plant size affecting stems, leaves, and fruit. Decreased size correlated with smaller cells and was accompanied by higher pigment contents and photosynthetic activities per leaf cross-section. Flavodoxin accumulated in green fruit but declined with ripening. Significant increases in HI were observed in flavodoxin-expressing lines due to the production of higher fruit number per plant in smaller plants. Therefore, overall yields can be enhanced by increasing plant density in the field. Metabolic profiling of ripe red fruit showed that levels of sugars, organic acids, and amino acids were similar or higher in transgenic plants, indicating that there was no trade-off between increased HI and fruit metabolite contents in flavodoxin-expressing plants. Taken together, our results show that flavodoxin has the potential to improve major agronomic traits when introduced in tomato.

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.

The Sugar-Signaling Hub: Overview of Regulators and Interaction with the Hormonal and Metabolic Network

Plant growth and development has to be continuously adjusted to the available resources. Their optimization requires the integration of signals conveying the plant metabolic status, its hormonal balance, and its developmental stage. Many investigations have recently been conducted to provide insights into sugar signaling and its interplay with hormones and nitrogen in the fine-tuning of plant growth, development, and survival. The present review emphasizes the diversity of sugar signaling integrators, the main molecular and biochemical mechanisms related to the sugar-signaling dependent regulations, and to the regulatory hubs acting in the interplay of the sugar-hormone and sugar-nitrogen networks. It also contributes to compiling evidence likely to fill a few knowledge gaps, and raises new questions for the future.