Reply: Interaction between Brassinosteroids and Gibberellins: Synthesis or Signaling? In Arabidopsis, Both!

Neoadjuvant Strategies for Triple Negative Breast Cancer: Current Evidence and Future Perspectives

Triple‐negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer, characterized by poor prognosis and limited therapeutic options. Although neoadjuvant chemotherapy (NACT) remains the established treatment approach, its suboptimal efficacy associated with TNBC highlight the urgent need for optimized treatment strategies to improve pathological complete response (pCR) rates. This review provides a comprehensive overview of recent advancements in neoadjuvant treatment for TNBC, emphasizing pivotal breakthroughs in therapeutic strategies and the ongoing pursuit of innovative approaches to enhance precision medicine. It emphasizes the clinical value of platinum‐based agents, such as carboplatin and cisplatin, which have shown significant improvements in pCR rates, particularly in TNBC patients with BRCA mutations. Additionally, the review explores progress in targeted therapies, including PARP inhibitors, AKT inhibitors, and Antiangiogenic agents, showcasing their potential for personalized treatment approaches. The integration of immunotherapy, particularly immune checkpoint inhibitor like pembrolizumab and atezolizumab, with chemotherapy has demonstrated substantial efficacy in high‐risk TNBC cases. Future research priorities include refining biomarker‐driven strategies, optimizing therapeutic combinations, developing antibody‐drug conjugates (ADCs) targeting TROP2 and other biomarkers, and reducing treatment‐related toxicity to develop safer and highly personalized neoadjuvant therapies. Furthermore, artificial intelligence has also emerged as a transformative tool in predicting treatment response and optimizing therapeutic decision‐making in TNBC. These advancements aim to improve long‐term outcomes and quality of life for patients with TNBC.

Manipulating GA-Related Genes for Cereal Crop Improvement

The global population is projected to experience a rapid increase in the future, which poses a challenge to global food sustainability. The "Green Revolution" beginning in the 1960s allowed grain yield to reach two billion tons in 2000 due to the introduction of semi-dwarfing genes in cereal crops. Semi-dwarfing genes reduce the gibberellin (GA) signal, leading to short plant stature, which improves the lodging resistance and harvest index under modern fertilization practices. Here, we reviewed the literature on the function of GA in plant growth and development, and the role of GA-related genes in controlling key agronomic traits that contribute to grain yield in cereal crops. We showed that: (1) GA is a significant phytohormone in regulating plant development and reproduction; (2) GA metabolism and GA signalling pathways are two key components in GA-regulated plant growth; (3) GA interacts with other phytohormones manipulating plant development and reproduction; and (4) targeting GA signalling pathways is an effective genetic solution to improve agronomic traits in cereal crops. We suggest that the modification of GA-related genes and the identification of novel alleles without a negative impact on yield and adaptation are significant in cereal crop breeding for plant architecture improvement. We observed that an increasing number of GA-related genes and their mutants have been functionally validated, but only a limited number of GA-related genes have been genetically modified through conventional breeding tools and are widely used in crop breeding successfully. New genome editing technologies, such as the CRISPR/Cas9 system, hold the promise of validating the effectiveness of GA-related genes in crop development and opening a new venue for efficient and accelerated crop breeding.

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

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

Brassinosteroids Benefit Plants Performance by Augmenting Arbuscular Mycorrhizal Symbiosis

Arbuscular mycorrhizal (AM) play an important role in improving plant growth and development. The interaction between phytohormones and AM symbiosis is gradually revealed. Here we examined the effect of Brassinosteroids (BR) on AM symbiosis and discussed the synergistic promotion of plant growth by BR and AM symbiosis. The xylophyta Eucalyptus grandis Hill (E. grandis) was inoculated with AM fungi Rhizoglomus irregularis R197198 (R. irregularis) and treated with different concentrations (0, 1, 10, and 100 nM) of 24-epibrassinolide (24-epiBL) for 6 weeks. With the increase of 24-epiBL concentration, E. grandis growth was firstly promoted and then inhibited, but inoculation with AM fungi alleviated this inhibition. 24-epiBL and R. irregularis colonization significantly improved E. grandis growth and antioxidant system response, and the synergistic effect was the best. Compared with the control group, 24-epiBL treatment significantly increased the mycorrhizal colonization and arbuscular abundance of AM fungi R. irregular in E. grandis roots. The expression of AM symbiosis maker genes was significantly increased by 24-epiBL treatment. Both 24-epiBL treatment and AM colonization upregulated gibberellins (GA) synthesis genes, but no inhibition caused by GA levels was found. 24-epiBL is a kind of synthetic highly active BR. Based on the results of 24-epiBL treatment, we hypothesized that BR actively regulates AM symbiosis regulates AM symbiosis without affecting GA-INSENSITIVE DWARF1 (GID1)-DELLA expression. The synergistic treatment of BR and AM symbiosis can significantly promote the growth and development of plants. IMPORTANCE Brassinosteroids (BR) and Arbuscular mycorrhizas (AM) symbiosis play an important role in improving plant growth and development. Previous studies have shown that there is a complex regulatory network between phytohormones and AM symbiosis. However, the interactions of BR-signaling and AM symbiosis are still poorly understood. Our results suggest that BR actively regulates the colonization and development of AM fungi, and AM fungal colonization can alleviate the inhibition of plant growth caused by excessive BR. In addition, BR actively regulates AM symbiosis, but does not primarily mediate gibberellins-DELLA interaction. The synergistic treatment of BR and AM symbiosis can significantly promote the growth and development of plants. The conclusions of this study provide a reference for phytohormones-AM symbiosis interaction.

HrCYP90B1 modulating brassinosteroid biosynthesis in sea buckthorn (Hippophae rhamnoides L.) against fruit fly (Rhagoletis batava obseuriosa Kol.) infection

Sea buckthorn is an important ecological and economic tree species, and its berries have been severely damaged by sea buckthorn fruit fly, Rhagoletis batava obseuriosa Kol. (Diptera: Tephritidae) (RBO). Brassinosteroid (BR) is widely involved in stress tolerance of plant. However, limited knowledge exists regarding the molecular mechanisms underlying insect resistance. Here, we found that BR content was much higher in sea buckthorn fruits with RBO infection than non-infection, and the damage rates of fruit with BR treatment were significantly lower than that of non-treatment. It indicated that BR could enhance RBO resistance in sea buckthorn. Several BR biosynthesis-related HrCYPs genes (CYP85A1/85A2/90A1/90B1/90C1/90D1/92A6/724B/734A1) were obtained and identified based on transcriptome analysis, of which the most up-regulated gene in fruits was HrCYP90B1 under RBO and mechanical damage. Overexpression of HrCYP90B1 in Arabidopsis thaliana showed BR and salicylic acid (SA) content was significantly increased, and the substrate campesterol (CR) of HrCYP90B1 content decreased. Further studies revealed that silencing HrCYP90B1 by virus-induced gene silencing resulted in decrease of BR, SA and defense-related enzymes contents, and increase of CR content. Silencing HrCYP90B1 also caused suppression of SA and activation of jasmonic acid pathways, enabling enhanced RBO susceptibility and more damage of fruits. Taken together, we obtained evidence that HrCYP90B1 was a positive regulator in RBO resistance improvement in sea buckthorn, which will provide comprehensive insights into the tree defense system of sea buckthorn to pest infection.

Modes of Brassinosteroid Activity in Cold Stress Tolerance

Cold stress is a significant environmental factor that negatively affects plant growth and development in particular when it occurs during the growth phase. Plants have evolved means to protect themselves from damage caused by chilling or freezing temperatures and some plant species, in particular those from temperate geographical zones, can increase their basal level of freezing tolerance in a process termed cold acclimation. Cold acclimation improves plant survival, but also represses growth, since it inhibits activity of the growth-promoting hormones gibberellins (GAs). In addition to GAs, the steroid hormones brassinosteroids (BRs) also take part in growth promotion and cold stress signaling; however, in contrast to Gas, BRs can improve cold stress tolerance with fewer trade-offs in terms of growth and yields. Here we summarize our current understanding of the roles of BRs in cold stress responses with a focus on freezing tolerance and cold acclimation pathways.

The GAMYB-like gene SlMYB33 mediates flowering and pollen development in tomato

GAMYBs are positive GA signaling factors that exhibit essential functions in reproductive development, particularly in anther and pollen development. However, there is no direct evidence of the regulation of any GAMYB in these biological processes in tomato (Solanum lycopersicum). Here, we identified a tomato GAMYB-like gene, SlMYB33, and characterized its specific roles. SlMYB33 is predominately expressed in the stamens and pistils. During flower development, high mRNA abundance of SlMYB33 is detected in both male and female organs, such as microspore mother cells, anthers, pollen grains, and ovules. Silencing of SlMYB33 leads to delayed flowering, aberrant pollen viability, and poor fertility in tomato. Histological analyses indicate that SlMYB33 exerts its function in pollen development in the mature stage. Further transcriptomic analyses imply that the knockdown of SlMYB33 significantly inhibits the expression of genes related to flowering in shoot apices, and alters the transcription of genes controlling sugar metabolism in anthers. Taken together, our study suggests that SlMYB33 regulates tomato flowering and pollen maturity, probably by modulating the expression of genes responsible for flowering and sugar metabolism, respectively.

Inhibitors of Brassinosteroid Biosynthesis and Signal Transduction

Chemical inhibitors are invaluable tools for investigating protein function in reverse genetic approaches. Their application bears many advantages over mutant generation and characterization. Inhibitors can overcome functional redundancy, their application is not limited to species for which tools of molecular genetics are available and they can be applied to specific tissues or developmental stages, making them highly convenient for addressing biological questions. The use of inhibitors has helped to elucidate hormone biosynthesis and signaling pathways and here we review compounds that were developed for the plant hormones brassinosteroids (BRs). BRs are steroids that have strong growth-promoting capacities, are crucial for all stages of plant development and participate in adaptive growth processes and stress response reactions. In the last two decades, impressive progress has been made in BR inhibitor development and application, which has been instrumental for studying BR modes of activity and identifying and characterizing key players. Both, inhibitors that target biosynthesis, such as brassinazole, and inhibitors that target signaling, such as bikinin, exist and in a comprehensive overview we summarize knowledge and methodology that enabled their design and key findings of their use. In addition, the potential of BR inhibitors for commercial application in plant production is discussed.

The Role of Dwarfing Traits in Historical and Modern Agriculture with a Focus on Rice

Semidwarf stature is a valuable agronomic trait in grain crops that reduces lodging and increases harvest index. A fundamental advance during the 1960s Green Revolution was the introduction of semidwarf cultivars of rice and wheat. Essentially, all semidwarf varieties of rice under cultivation today owe their diminished stature to a specific null mutation in the gibberellic acid (GA) biosynthesis gene, SD1 However, it is now well-established that, in addition to GAs, brassinosteroids and strigolactones also control plant height. In this review, we describe the synthesis and signaling pathways of these three hormones as understood in rice and discuss the mutants and transgenics in these pathways that confer semidwarfism and other valuable architectural traits. We propose that such genes offer underexploited opportunities for broadening the genetic basis and germplasm in semidwarf rice breeding.

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.

OsmiR396d Affects Gibberellin and Brassinosteroid Signaling to Regulate Plant Architecture in Rice

Genetic improvement of plant architecture is one of the strategies for increasing the yield potential of rice (Oryza sativa). Although great progress has been made in the understanding of plant architecture regulation, the precise mechanism is still an urgent need to be revealed. Here, we report that over-expression of OsMIR396d in rice results in semidwarf and increased leaf angle, a typical phenotype of brassinosteroid (BR) enhanced mutant. OsmiR396d is involved in the interaction network of BR and gibberellin (GA) signaling. In OsMIR396d over-expression plants, BR signaling was enhanced. In contrast, both the signaling and biosynthesis of GA were impaired. BRASSINAZOLE-RESISTANT1, a core transcription activator of BR signaling, directly promoted the accumulation of OsmiR396d, which controlled BR response and GA biosynthesis by regulating the expression of different target genes respectively. GROWTH REGULATING FACTOR 6, one of OsmiR396d targets, participated in GA biosynthesis and signal transduction but was not directly involved in BR signaling. This study provides a new insight into the understanding of interaction between BR and GA from multiple levels on controlling plant architecture.

Mathematical modelling and analysis of the brassinosteroid and gibberellin signalling pathways and their interactions

The plant hormones brassinosteroid (BR) and gibberellin (GA) have important roles in a wide range of processes involved in plant growth and development. In this paper we derive and analyse new mathematical models for the BR signalling pathway and for the crosstalk between the BR and GA signalling pathways. To analyse the effects of spatial heterogeneity of the signalling processes, along with spatially-homogeneous ODE models we derive coupled PDE-ODE systems modelling the temporal and spatial dynamics of molecules involved in the signalling pathways. The values of the parameters in the model for the BR signalling pathway are determined using experimental data on the gene expression of BR biosynthetic enzymes. The stability of steady state solutions of our mathematical model, shown for a wide range of parameters, can be related to the BR homeostasis which is essential for proper function of plant cells. Solutions of the mathematical model for the BR signalling pathway can exhibit oscillatory behaviour only for relatively large values of parameters associated with transcription factor brassinazole-resistant1's (BZR) phosphorylation state, suggesting that this process may be important in governing the stability of signalling processes. Comparison between ODE and PDE-ODE models demonstrates distinct spatial distribution in the level of BR in the cell cytoplasm, however the spatial heterogeneity has significant effect on the dynamics of the averaged solutions only in the case when we have oscillations in solutions for at least one of the models, i.e. for possibly biologically not relevant parameter values. Our results for the crosstalk model suggest that the interaction between transcription factors BZR and DELLA exerts more influence on the dynamics of the signalling pathways than BZR-mediated biosynthesis of GA, suggesting that the interaction between transcription factors may constitute the principal mechanism of the crosstalk between the BR and GA signalling pathways. In general, perturbations in the GA signalling pathway have larger effects on the dynamics of components of the BR signalling pathway than perturbations in the BR signalling pathway on the dynamics of the GA pathway. The perturbation in the crosstalk mechanism also has a larger effect on the dynamics of the BR pathway than of the GA pathway. Large changes in the dynamics of the GA signalling processes can be observed only in the case where there are disturbances in both the BR signalling pathway and the crosstalk mechanism. Those results highlight the robustness of the GA signalling pathway.

Brassinosteroids Regulate OFP1, a DLT Interacting Protein, to Modulate Plant Architecture and Grain Morphology in Rice

Brassinosteroids (BRs) regulate important agronomic traits in rice, including plant height, leaf angle, and grain size. However, the underlying mechanisms remain not fully understood. We previously showed that GSK2, the central negative regulator of BR signaling, targets DLT, the GRAS family protein, to regulate BR responses. Here, we identified Ovate Family Protein 1 (OFP1) as a DLT interacting protein. OFP1 was ubiquitously expressed and the protein was localized in both cytoplasm and nucleus. Overexpression of OFP1 led to enlarged leaf angles, reduced plant height, and altered grain shape, largely resembled DLT overexpression plants. Genetic analysis showed that the regulation of plant architecture by OFP1 depends on DLT function. In addition, we found OFP1 was greatly induced by BR treatment, and OsBZR1, the critical transcription factor of BR signaling, was physically associated with the OFP1 promoter. Moreover, we showed that gibberellin synthesis was greatly repressed in OFP1 overexpression plants, suggesting OFP1 participates in the inhibition of plant growth by high BR or elevated BR signaling. Furthermore, we revealed that OFP1 directly interacts with GSK2 kinase, and inhibition of the kinase activity significantly promotes OFP1 protein accumulation in plant. Taken together, we identified OFP1 as an additional regulator of BR responses and revealed how BRs promote OFP1 at both transcription and protein levels to modulate plant architecture and grain morphology in rice.