Brassinosteroid Treatment Research Articles

Brassinosteroids: An Innovative Compound Family That Could Affect the Growth, Ripening, Quality, and Postharvest Storage of Fleshy Fruits

Brassinosteroids (BRs), a new family of plant hormones, have been used in a range of food staples, oil crops, and cereals. However, the scientific literature pertaining to their use in fleshy fruits remains scarce. This review presents, for the first time, the knowledge developed over the last decade on the role of BR preharvest treatments in crop yield and fruit quality properties at harvest and during storage, although information about the effects of BR postharvest treatments is also addressed. This review revealed that 24-epibrassinolide is the most used BR analogue in research experiments, either as a pre- or postharvest treatment, with doses ranging from 0.1 to 15 μM. Additionally, most of the research has been conducted on non-climacteric fruit species. In most of these preharvest treatments, an increase in crop yield has been reported, as well as enhanced anthocyanin concentration in red-coloured fruit. In addition, increases in firmness, total soluble solids, and phenolic content have also been observed. On the other hand, BR postharvest treatments led to the maintenance of these fruit quality properties during storage due to increased antioxidant systems, either enzymatic or non-enzymatic ones. Finally, as future perspectives, it is proposed to extend the research about BR treatments to other climacteric fruits and to deepen the knowledge of how BRs regulate physiological aspects from preharvest to postharvest. Furthermore, it is essential to investigate the role of BRs in the prevention of rot and biotic stress.

Roles of Nitric Oxide and Brassinosteroid in Improving Fruit Quality during Postharvest: Potential Regulators?

Most postharvest fruits are highly perishable, which directly impairs fruit taste and causes an economic loss of fresh products. Thus, it is necessary to find effective techniques to alleviate this issue. Recently, nitric oxide (NO) and brassinosteroid (BR) have been developed as postharvest alternatives to improve fruit quality. This work mainly reviews the recent processes of NO and BR in improving fruit quality during postharvest. Exogenous NO or BR treatments delayed fruit senescence, enhanced disease resistance, and alleviated chilling injury in postharvest fruit, and potential physiological and biochemical mechanisms mainly include (1) enhancing antioxidant and defense ability, (2) affecting ethylene biosynthesis, (3) regulating sugar and energy metabolism, (4) mediating plant hormone signaling, and (5) regulating protein S-nitrosylation and DNA methylation. This review concludes the functions and mechanisms of NO and BR in improving postharvest fruit quality. Additionally, a specific finding is the possible crosstalk of applications of NO and BR during postharvest fruit storage, which provides new insights into the applicability of NO and BR for delaying fruit senescence, enhancing disease resistances of fruit, and alleviating chilling injury in postharvest fruit.

Characterization of the Bax Inhibitor-1 Family in Cauliflower and Functional Analysis of BobBIL4.

The Bax inhibitor-1 (BI-1) gene family, which is important for plant growth, development, and stress tolerance, remains largely unexplored in cauliflower. In this study, we identified and characterized cauliflower BI-1 family genes. Based on aligned homologous sequences and collinearity with Arabidopsis genes, we identified nine cauliflower BI-1 genes, which encode proteins that varied in length, molecular weight, isoelectric point, and predicted subcellular localization, including the Golgi apparatus, plasma membrane, and various compartments within the chloroplast. Phylogenetic analyses detected evolutionary conservation and divergence among these genes. Ten structural motifs were identified, with Motif 5 found to be crucial for inhibiting apoptosis. According to the cis-regulatory elements in their promoters, these genes likely influence hormone signaling and stress responses. Expression profiles among tissues highlighted the functional diversity of these genes, with particularly high expression levels observed in the silique and root. Focusing on BobBIL4, we investigated its role in brassinosteroid (BR)-mediated root development and salt stress tolerance. BobBIL4 expression levels increased in response to BR and salt treatments. The functional characterization of this gene in Arabidopsis revealed that it enhances root growth and salinity tolerance. These findings provide insights into BI-1 gene functions in cauliflower while also highlighting the potential utility of BobBIL4 for improving crop stress resistance.

Revealing mechanistic basis of ameliorating detrimental effects of cadmium in cherry tomatoes by exogenous application of melatonin and brassinosteroids

Increased anthropogenic activities over the last decades have led to a gradual increase in cadmium content in the soil, which, due to its high mobility in soil, makes Cd accumulation in plants a serious threat to the health of animals and humans. Plant hormones including melatonin (Mel) and brassinosteroids (BR) are known to provide tolerance against various abiotic stresses. In this work, the role of combined and separate exogenous application of Mel and BR on Cd stress in cherry tomato plants was examined. Cd stress significantly reduced tomato growth by inducing oxidative stress and reduced K+ uptake in roots and shoots. Combined application of Mel and BR reduced detrimental effects of Cd in tomato by (i) reducing Cd accumulation in the shoot; (ii) increasing the activities of different antioxidants (SOD, CAT, APX, GR); (iii) triggering higher expression of genes relating to Cd vacuolar sequestration (Na+/H+ EXCHANGER, SlNHX1; NATURAL RESISTANCE-ASSOCIATED MACROPHAGE PROTEIN 6, SlNRAMP6), and Cd transport and detoxification (HEAVY-METAL-ASSOCIATED 3, SlHMA3; PLANT CADMIUM RESISTANT 2, SlPCR2); and (iv) improving plant K+ homeostasis and contents in root and shoot. The latter trait was associated with the reduced gene expression of K+-permeable outward rectifying channel (SlGORK3), and transcriptional upregulation of high affinity potassium transporter 5 (SIHAK5) under Cd stress. A separate application of Mel and BR showed tissue-specific regulation of tomato growth and Cd tolerance by regulating antioxidant activities, K+ uptake, Cd uptake, and translocation from root to shoot and their endogenous contents. Melatonin per se was more effective in improving Cd tolerance in shoot while beneficial BR effects were more pronounced in roots, and their combined application was effective in both tissues. Taken together, reported results show tissue-specific regulation of Cd tolerance by Mel and BR in cherry tomato plants and demonstrate the efficiency of combined Mel + BR treatment as a practical tool to reduce Cd accumulation and mitigate its negative effects on plant growth.

Maintaining postharvest quality and enhancing shelf-life of bell pepper (Capsicum annuum L.) using brassinosteroids: A novel approach

Bell pepper is a major vegetable crop of global commercial interest, but the postharvest quality is constrained by faster deterioration and senescence. Brassinosteroids (BRs), are an emerging and novel biomolecule that delay ripening and senescence in various vegetables. Freshly harvested bell pepper fruit were immersed in an aqueous solution of BRs concentrations (0, 2, 5, 7 and 10 μM) for 20 min and subsequently stored for 20 d at 10 ± 1°C, 85–90% RH. The bell pepper treated with 10 μM BRs significantly reduced respiration rate (∼2.3 fold), delayed weight loss (∼2.2 fold), and retained higher firmness (∼2.5 fold), total phenolic (∼1.7 fold), flavonoid (∼1.7 fold), proline (∼2 fold) and ascorbic acid content (∼2 fold) over the control fruit at the end of cold storage. Also, it retained higher DPPH radical scavenging (∼1.8 fold) and antioxidant enzyme activity (∼1.5 fold) over the control at the end of cold storage. Moreover, BRs treated bell pepper exhibited reduced malondialdehyde accumulation and delayed capsaicin, and chlorophyll degradation. Remarkably, 10 μM BRs treatment prolonged the shelf-life of bell pepper up to 20 d (10 d extra over control) without compromising quality and sensory acceptability.

Effects of concentration and time of brassinosteroid treatment on growth and yield of soybean under drought stress conditions

Soybean (Glycine max (L.) Merrill.) is an essential food and industrial crop, but it can be heavily affected by drought, especially during the pod growth stage. Brassinosteroids (BRs) are reported to alleviate drought stress, but the effectiveness may depend strongly on BR concentration and timing of the application, and no research has investigated this issue. This study aimed to determine the suitable concentration of BRs and time of treatment to help soybean plants withstand drought conditions during pod growth. The experiment was conducted with a completely randomized design, with four concentrations of BRs: 0 ppm (water) (B0), 0.1 ppm (B1), 0.2 ppm (B2), 0.3 ppm (B3), and three-time points for the application of BR treatment: soaking before sowing (T1), leaf spray when 50% of plants flowered (T2), leaf spray when 50% of the plants had pod at least 0.5 cm in length (T3). The results showed that when treated with different concentrations and treatment times of BRs, there was no difference in plant growth and development. However, there were differences in the yield of soybean plants. Specifically, treatment B2T2 had the highest total number of firm pods and the highest number of firm seeds at 22.2 and 44.6, respectively, with the weight of 100 seeds reaching 17.9 g, leading to the highest actual yield of 97.0 g/plot. These results indicate that with appropriate concentration and timing (0.2 ppm during flowering), the application of BRs can significantly alleviate drought stress effects on soybean plants during pod growth, improving seed yield and quality.

The Effects of Brassinosteroids on Nitrogen Utilization in Rice

Nitrogen and brassinosteroids (BRs) play a vital role in modulating the growth, development, and yield of rice. However, the influences of BRs on nitrogen assimilation and metabolism in rice are not fully understood. In this study, we analyzed the impact of BRs on nitrogen utilization in rice using the indica variety ‘Zhongjiazao 17’ and the japonica variety ‘Nipponbare’ in hydroponic conditions. The results showed that BR treatment could efficiently elevate nitrate and ammonium nitrogen accumulation in both shoots and roots. Furthermore, some genes involved in the uptake of nitrate and ammonium in roots were stimulated by BRs, though we noted subtle variances between the two rice cultivars. Moreover, BRs augmented the activity of nitrate reductase (NR) and glutamine synthetase (GS) in roots, along with NR in shoots. Interestingly, BRs also spiked the total free amino acid content in both the shoots and roots. Gene expression analysis uncovered a robust induction by BRs of NR genes and GS-related genes in the roots of both ‘Nipponbare’ and ‘Zhongjiazao 17’. Collectively, our data suggest that BRs significantly enhance the accumulation of both nitrate and ammonium in rice and trigger a series of reactions related to nitrogen utilization.

WGCNA analysis of the effect of exogenous BR on leaf angle of maize mutant lpa1

Leaf angle, as one of the important agronomic traits of maize, can directly affect the planting density of maize, thereby affecting its yield. Here we used the ZmLPA1 gene mutant lpa1 to study maize leaf angle and found that the lpa1 leaf angle changed significantly under exogenous brassinosteroid (BR) treatment compared with WT (inbred line B73). Transcriptome sequencing of WT and lpa1 treated with different concentrations of exogenous BR showed that the differentially expressed genes were upregulated with auxin, cytokinin and brassinosteroid; Genes associated with abscisic acid are down-regulated. The differentially expressed genes in WT and lpa1 by weighted gene co-expression network analysis (WGCNA) yielded two gene modules associated with maize leaf angle change under exogenous BR treatment. The results provide a new theory for the regulation of maize leaf angle by lpa1 and exogenous BR.

Comprehensive investigation of BZR gene family in four dicots and the function of PtBZR9 and PtBZR12 under drought stress

Brassinazole-resistant (BZR) transcription factor plays an important role in plant growth and stress resistance through brassinosteroid (BR) signal transduction. However, systematic analysis of the BZR family in dicots remains limited. In this study, we conducted a genome-wide study of four typical dicots: Arabidopsis thaliana, Carica papaya, Vitis vinifera and Populus trichocarpa. Thirty-four BZR gene family members were identified and classified them into three subfamilies. Analysis of promoter and expression patterns revealed crucial role of a pair of homologous BZR genes, PtBZR9 and PtBZR12, in poplar may play a critical role under abiotic stress. PtBZR9 and PtBZR12 were localised in the nucleus and exhibited mutual interactions. Moreover, transient overexpression (OE) of PtBZR9 and PtBZR12 in poplar enhanced tolerance to drought stress. The phenotypic and physiological characteristics of PtBZR9 and PtBZR12 OE in Arabidopsis mirrored those of transient OE in the poplar. Additionally, PtBZR9 and PtBZR12 can bind to the E-box element. Under exogenous BR treatment, transgenic lines displayed a greater decrease in root length than the wild type. Thus, these findings provide a solid foundation for future research on the complex regulatory mechanisms of BZR genes.

Effects of seed coating and priming with exogenous brassinosteroid on tobacco seed germination

ABSTRACT Brassinosteroid (BR) is a hormone known for its crucial role in seed germination promotion. However, there is a limited understanding of potential application in tobacco seed. In this study, we investigated various active ingredients for seed coating to enhance tobacco seed germination. It revealed that seed coating with 0.0500 ppm BR and priming with 0.01 ppm BR significantly increased seed germination rates, especially in low-temperature conditions. In addition, the combined use BR with priming and seed coating exhibited a substantial improvement in seed germination rates and promoted seedling growth. Through transcriptional analysis, it found that BR treatment regulates the expression of genes associated with DNA synthesis, cell wall organization and glucan metabolic process involved in seed dormancy and seedling growth. Overall, these results provide valuable insights into the utilization of seed coating and priming techniques, particularly with the inclusion of BR, to enhance tobacco seed germination and facilitate seedling emergence.

Exogenous applications of brassinosteroids promote secondary xylem differentiation in Eucalyptus grandis.

Brassinosteroids (BRs) play many pivotal roles in plant growth and development, especially in cell elongation and vascular development. Although its biosynthetic and signal transduction pathway have been well characterized in model plants, their biological roles in Eucalyptus grandis, a major hardwood tree providing fiber and energy worldwide, remain unclear. Here, we treated E. grandis plantlets with 24-epibrassinolide (EBL), the most active BR and/or BR biosynthesis inhibitor brassinazole. We recorded the plant growth and analyzed the cell structure of the root and stem with histochemical methods; then, we performed a secondary growth, BR synthesis, and signaling-related gene expression analysis. The results showed that the BRs dramatically increased the shoot length and diameter, and the exogenous BR increased the xylem area of the stem and root. In this process, EgrBRI1, EgrBZR1, and EgrBZR2 expression were induced by the BR treatment, and the expressions of HD-ZIPIII and cellulose synthase genes were also altered. To further verify the effect of BRs in secondary xylem development in Eucalyptus, we used six-month-old plants as the material and directly applied EBL to the xylem and cambium of the vertical stems. The xylem area, fiber cell length, and cell numbers showed considerable increases. Several key BR-signaling genes, secondary xylem development-related transcription factor genes, and cellulose and lignin biosynthetic genes were also considerably altered. Thus, BR had regulatory roles in secondary xylem development and differentiation via the BR-signaling pathway in this woody plant.

Physiological Characteristics and Transcriptome Analysis of Exogenous Brassinosteroid-Treated Kiwifruit.

Brassinosteroids (BRs) play pivotal roles in improving plant stress tolerance. To investigate the mechanism of BR regulation of salt tolerance in kiwifruit, we used 'Hongyang' kiwifruit as the test material. We exposed the plants to 150 mmol/L NaCl stress and irrigated them with exogenous BR (2,4-epibrassinolide). The phenotypic analysis showed that salt stress significantly inhibited photosynthesis in kiwifruit, leading to a significant increase in the H2O2 content of leaves and roots and a significant increase in Na+/K+, resulting in oxidative damage and an ion imbalance. BR treatment resulted in enhanced photosynthesis, reduced H2O2 content, and reduced Na+/K+ in leaves, alleviating the salt stress injury. Furthermore, transcriptome enrichment analysis showed that the differentially expressed genes (DEGs) related to BR treatment are involved in pathways such as starch and sucrose metabolism, pentose and glucuronate interconversions, and plant hormone signal transduction, among others. Among the DEGs involved in plant hormone signal transduction, those with the highest expression were involved in abscisic acid signal transduction. Moreover, there was a significant increase in the expression of the AcHKT1 gene, which regulates ion transduction, and the antioxidant enzyme AcFSD2 gene, which is a key gene for improving salt tolerance. The data suggest that BRs can improve salt tolerance by regulating ion homeostasis and reducing oxidative stress.

The roles of brassinosteroids and methyl jasmonate on postharvest grape by regulating the interaction between VvDWF4 and VvTIFY 5 A

Brassinosteroids (BRs) and methyl jasmonate (MeJA) are known for the regulation of plant development, and the crosstalk between them is important for plant growth. However, the interaction between them in the development of postharvest fruit is unresolved. We found that BR treatment enhanced the accumulation of sugar composition and aroma content, reduced the content of organic acids (such as tartaric acid) and promoted the coloring of grape callus. After the application of MeJA, the acidity increased and the sugar content decreased. The physiological data showed that exogenous BR also attenuated the JA inhibition of postharvest ripening in grape. DWF4 is a key enzyme in the BR biosynthetic pathway, and it can effectively regulate the content of endogenous BRs. TIFY 5 A, which belongs to the Jasmonate ZIM-domain (JAZ) family, can be baited by DWF4 through the Y2H experiment. TIFY 5 A represses the expression of dihydroflavonol-4-reductase (DFR) which plays a key role in the synthesis of anthocyanins, while this will be alleviated by VvDWF4. The interaction between TIFY 5 A and DWF4 contributes to the cross talk between JA and BR signalling pathways. This is also verified by the transgenic experimental results. The results in this paper provides a new insight into the relationship between BR and JA signalling pathways, which is important to the regulation of the postharvest ripening of grape.

Preharvest 24-epibrassinolide treatment prolongs harvest duration and shelf life in sweet corn

Sweet corn is perishable and have limited harvest duration and shelf life due to their quality deterioration. Reactive oxygen species (ROS) are one of the most predominant factors for maintaining quality of sweet corn during and after harvest. Brassinosteroids (BRs) can enhance the activity of antioxidant enzymes and decrease the ROS level in plants. In this study, we found that a bioactive BR (24-epibrassinolide, EBR) treatment before harvest markedly inhibited change of quality indicators (MDA content, weight loss rate, and soluble sugar content) during and after harvest. Further analysis revealed that EBR promoted the activity and transcriptions of antioxidant enzymes, maintaining lower ROS level in kernels. Meanwhile, exogenous EBR increased the expression level of genes controlling sucrose transport in sweet corn kernels. Bioinformatics and binding analysis identified that BR transcription factor ZmBES1/ZmBZR1-10 might potentially bind to and upregulate transcriptions of antioxidant enzyme genes including SOD and POD genes, and sucrose transport-related genes including SUT and SWEET genes. These results indicated that exogenous application of EBR ameliorates quality during and after harvest by improving the antioxidant capacity and photosynthetic assimilates accumulation rate of sweet corn, thus prolonging harvest duration and shelf life in sweet corn.

Exogenous BR delayed peach fruit softening by inhibiting pectin degradation enzyme genes.

Peach fruit deteriorates and senesces rapidly when stored at room temperature. Brassinosteroids (BRs) play an important role in regulating plant growth and development and maintaining fruit quality. However, little information is available on the effect of BRs on the senescence of harvested peach fruit. In this study, different concentrations of BR were used to treat 'Hongniang' peach fruit, and the results showed that 10 μM BR was the most beneficial concentration to delay the senescence of peach fruits. BR treatment delayed the decrease of fruit firmness, the release of ethylene, the increase in water-soluble pectin (WSP) and ionic-soluble pectin (ISP) content and the decrease in covalently bound pectin (CBP) content, inhibited the activities of pectin degradation enzymes, and inhibited the gene expression of PpPME1/3, PpPG, PpARF2, and PpGAL2/16. In addition, BR treatment also inhibited the expression of PpBES1-5/6. Cis-acting regulatory element analysis of pectin degradation enzyme promoters showed that many of them contained BES1 binding elements. All the above results showed that BR treatment had a positive effect on delaying the senescence of peach fruit and prolonging its storage period.

The rice transcription factors OsHOX22 and OsHOX24 oppositely modulate the lamina joint inclination

OsHOX22 and OsHOX24 are members of the homeodomain-leucine zipper I (HD-Zip I) subfamily of transcription factors (TFs) involved in ABA-mediated salt and drought tolerance. Phylogenetic analyses resolve these TFs into the same subgroup (γ-clade). We used CRISPR/Cas9 technology to obtain two Japonica CVs. Kitaake edited rice lines (edOsHOX22 and edOsHOX24) by a non-homologous end-joining mechanism. These plants displayed opposite phenotypes in the lamina joint inclination of the second leaf of 9-day-old seedlings. The edOsHOX22 genotype presented a larger leaf angle than the wild-type (WT), resembling plants with increased endogenous brassinosteroid (BR) levels. In addition, the BR treatment repressed OsHOX22 expression in WT plants. Otherwise, the edOsHOX24 plants exhibited the opposite phenotype, and BRs induced OsHOX24 expression. This evidence suggested a mutual negative and positive regulation between OsHOX22 and OsHOX24 and the phytohormone, respectively. Besides, BR biosynthesis and signaling genes exhibited altered levels in edOsHOX22 and edOsHOX24 plants compared with controls. Notably, under abiotic stress, they agonistically modified their expression, and the ABA signaling cascade masked the BR response, closing the leaf angle in both genotypes. Our findings indicated that OsHOX22 and OsHOX24 play differential roles in the lamina joint inclination event. This study contributes two new players to the complex mechanisms involved in the leaf angle opening under different environmental cues in rice.

The Leucine-Rich Repeat Receptor-Like Kinase Protein TaSERK1 Positively Regulates High-Temperature Seedling Plant Resistance to Puccinia striiformis f. sp. tritici by Interacting with TaDJA7.

Somatic embryogenesis receptor kinases (SERKs) belong to the leucine-rich repeat receptor-like kinase (LRR-RLK) subfamily, and many LRR-RLKs have been proven to play a key role in plant immune signal transmission. However, the functions of SERKs in resistance to stripe rust caused by Puccinia striiformis f. sp. tritici remains unknown. Here, we identified a gene, TaSERK1, from Xiaoyan 6, a wheat cultivar possessing high-temperature seedling-plant (HTSP) resistance to the fungal pathogen P. striiformis f. sp. tritici and expresses its resistance at the seedling stage. The expression level of TaSERK1 was upregulated upon P. striiformis f. sp. tritici inoculation under relatively high temperatures. The transcriptional level of TaSERK1 was significantly increased under exogenous salicylic acid and brassinosteroids treatments. The barley stripe mosaic virus-induced gene silencing assay indicated that TaSERK1 positively regulated the HTSP resistance to stripe rust. The transient expression of TaSERK1 in tobacco leaves confirmed its subcellular localization on the plasma membrane. Furthermore, TaSERK1 interacted with and phosphorylated the chaperone protein TaDJA7, which belongs to the heat shock protein 40 subfamily. Silencing TaDJA7 compromised the HTSP resistance to stripe rust. The results indicated that when the membrane immune receptor TaSERK1 perceives the P. striiformis f. sp. tritici infection under relatively high temperatures, it transmits the signal to TaDJA7 to activate HTSP resistance to the pathogen.

Scaffold protein RACK1 regulates BR signaling by modulating the nuclear localization of BZR1.

Brassinosteroids (BRs) are a group of plant-specific steroid hormones, which induces the rapid nuclear localization of the positive transcriptional factors BRASSINAZOLE RESISTANT1/2 (BZR1/2). However, the mechanisms underlying the regulation of nucleocytoplasmic shuttling of BZR1 remain to be fully elucidated. In this study, we show that the scaffold protein Receptor for Activated C Kinase 1 (RACK1) from Arabidopsis is involved in BR signaling cascades through mediating the nuclear localization of BZR1, which is tightly retained in the cytosol by the conserved scaffold protein 14-3-3s. RACK1 can interact with BZR1 and competitively decrease the 14-3-3 interaction with BZR1 in cytosol, which efficiently enhances the nuclear localization of BZR1. 14-3-3 also retains RACK1 in cytosol through their interaction. Conversely, BR treatment enhances the nuclear localization of BZR1 by disrupting the 14-3-3 interaction with RACK1 and BZR1. Our study uncovers a new mechanism that integrates two kinds of conserved scaffold proteins (RACK1 and 14-3-3) coordinating BR signaling event.

The transcriptional hub SHORT INTERNODES1 integrates hormone signals to orchestrate rice growth and development.

Plants have evolved sophisticated mechanisms to coordinate their growth and stress responses via integrating various phytohormone signaling pathways. However, the precise molecular mechanisms orchestrating integration of the phytohormone signaling pathways remain largely obscure. In this study, we found that the rice (Oryza sativa) short internodes1 (shi1) mutant exhibits typical auxin-deficient root development and gravitropic response, brassinosteroid (BR)-deficient plant architecture and grain size as well as enhanced abscisic acid (ABA)-mediated drought tolerance. Additionally, we found that the shi1 mutant is also hyposensitive to auxin and BR treatment but hypersensitive to ABA. Further, we showed that OsSHI1 promotes the biosynthesis of auxin and BR by activating the expression of OsYUCCAs and D11, meanwhile dampens ABA signaling by inducing the expression of OsNAC2, which encodes a repressor of ABA signaling. Furthermore, we demonstrated that 3 classes of transcription factors, AUXIN RESPONSE FACTOR 19 (OsARF19), LEAF AND TILLER ANGLE INCREASED CONTROLLER (LIC), and OsZIP26 and OsZIP86, directly bind to the promoter of OsSHI1 and regulate its expression in response to auxin, BR, and ABA, respectively. Collectively, our results unravel an OsSHI1-centered transcriptional regulatory hub that orchestrates the integration and self-feedback regulation of multiple phytohormone signaling pathways to coordinate plant growth and stress adaptation.

The brassinosteroid signaling component SlBZR1 promotes tomato fruit ripening and carotenoid accumulation.

The plant hormone ethylene is essential for climacteric fruit ripening, although it is unclear how other phytohormones and their interactions with ethylene might affect fruit ripening. Here, we explored how brassinosteroids (BRs) regulate fruit ripening in tomato (Solanum lycopersicum) and how they interact with ethylene. Exogenous BR treatment and increased endogenous BR contents in tomato plants overexpressing the BR biosynthetic gene SlCYP90B3 promoted ethylene production and fruit ripening. Genetic analysis indicated that the BR signaling regulators Brassinazole-resistant1 (SlBZR1) and BRI1-EMS-suppressor1 (SlBES1) act redundantly in fruit softening. Knocking out SlBZR1 inhibited ripening through transcriptome reprogramming at the onset of ripening. Combined transcriptome deep sequencing and chromatin immunoprecipitation followed by sequencing identified 73 SlBZR1-repressed targets and 203 SlBZR1-induced targets involving major ripening-related genes, suggesting that SlBZR1 positively regulates tomato fruit ripening. SlBZR1 directly targeted several ethylene and carotenoid biosynthetic genes to contribute to the ethylene burst and carotenoid accumulation to ensure normal ripening and quality formation. Furthermore, knock-out of Brassinosteroid-insensitive2 (SlBIN2), a negative regulator of BR signaling upstream of SlBZR1, promoted fruit ripening and carotenoid accumulation. Taken together, our results highlight the role of SlBZR1 as a master regulator of tomato fruit ripening with potential for tomato quality improvement and carotenoid biofortification.