Brassinosteroid Regulates Root Development with Highly Redundant Genes in Hexaploid Wheat

TaGSK3 regulates wheat development and stress adaptation through BR-dependent and BR-independent pathways

The GSK3/SHAGGY-like kinase plays critical roles in plant development and response to stress, but its specific function remains largely unknown in wheat (Triticum aestivum L.). In this study, we investigated the function of TaGSK3, a GSK3/SHAGGY-like kinase, in wheat development and response to stress. Our findings demonstrated that TaGSK3 mutants had significant effects on wheat seedling development and brassinosteroid (BR) signalling. Quadruple and quintuple mutants showed amplified BR signalling, promoting seedling development, while a sextuple mutant displayed severe developmental defects but still responded to exogenous BR signals, indicating redundancy and non-BR-related functions of TaGSK3. A gain-of-function mutation in TaGSK3-3D disrupted BR signalling, resulting in compact and dwarf plant architecture. Notably, this mutation conferred significant drought and heat stress resistance of wheat, and enhanced heat tolerance independent of BR signalling, unlike knock-down mutants. Further research revealed that this mutation maintains a higher relative water content by regulating stomatal-mediated water loss and maintains a lower ROS level to reduces cell damage, enabling better growth under stress. Our study provides comprehensive insights into the role of TaGSK3 in wheat development, stress response, and BR signal transduction, offering potential for modifying TaGSK3 to improve agronomic traits and enhance stress resistance in wheat.

BR regulates wheat root salt tolerance by maintaining ROS homeostasis

MAIN CONCLUSION

Trace amounts of epibrassinolide (EpiBL) could partially rescue wheat root length inhibition in salt-stressed situation by scavenging ROS, and ectopic expression of TaDWF4 or TaBAK1 enhances root salt tolerance in Arabidopsis by balancing ROS level. Salt stress often leads to ion toxicity and oxidative stress, causing cell structure damage and root development inhibition in plants. While prior research indicated the involvement of exogenous brassinosteroid (BR) in plant responses to salt stress, the precise cytological role and the function of BR in wheat root development under salt stress remain elusive. Our study demonstrates that 100 mM NaCl solution inhibits wheat root development, but 5 nM EpiBL partially rescues root length inhibition by decreasing H2O2 content, oxygen free radical (OFR) content, along with increasing the peroxidase (POD) and catalase (CAT) activities in salt-stressed roots. The qRT-PCR experiment also shows that expression of the ROS-scavenging genes (GPX2 and CAT2) increased in roots after applying BR, especially during salt stress situation. Transcriptional analysis reveals decreased expression of BR synthesis and root meristem development genes under salt stress in wheat roots. Differential expression gene (DEG) enrichment analysis highlights the significant impact of salt stress on various biological processes, particularly "hydrogen peroxide catabolic process" and "response to oxidative stress". Additionally, the BR biosynthesis pathway is enriched under salt stress conditions. Therefore, we investigated the involvement of wheat BR synthesis gene TaDWF4 and BR signaling gene TaBAK1 in salt stress responses in roots. Our results demonstrate that ectopic expression of TaDWF4 or TaBAK1 enhances salt tolerance in Arabidopsis by balancing ROS (Reactive oxygen species) levels in roots.

Wheat type one protein phosphatase promotes salt and osmotic stress tolerance in arabidopsis via auxin-mediated remodelling of the root system

The control of optimal root growth and plant stress responses depends largely on a variety of phytohormones among which auxin and brassinosteroids (BRs) are the most influential. We have previously reported that the durum wheat type 1 protein phosphatase TdPP1 participates in the control of root growth by modulating BR signaling. In this study, we pursue our understanding of how TdPP1 fulfills this regulatory function on root growth by evaluating the physiological and molecular responses of Arabidopsis TdPP1 over-expressing lines to abiotic stresses. Our results showed that when exposed to 300 mM Mannitol or 100 mM NaCl, the seedlings of TdPP1 over-expressors exhibit modified root architecture with higher lateral root density, and longer root hairs concomitant with a lower inhibition of the primary root growth. These lines also exhibit faster gravitropic response and a decrease in primary root growth inhibition when exposed to high concentrations of exogenous IAA. On another hand, a cross between TdPP1 overexpressors and DR5:GUS marker line was performed to monitor auxin accumulation in roots. Remarkably, the TdPP1 overexpression resulted in an enhanced auxin gradient under salt stress with a higher accumulation in primary and lateral root tips. Moreover, TdPP1 transgenics exhibit a significant induction of a subset of auxin-responsive genes under salt stress conditions. Therefore, our results reveal a role of PP1 in enhancing auxin signaling to help shape greater root plasticity thus improving plant stress resilience.

24-epibrassinolide improves cadmium tolerance and lateral root growth associated with regulating endogenous auxin and ethylene in Kentucky bluegrass

The application of phytohormones is a viable technique to increase the efficiency of phytoremediation in heavy metal-contaminated soils. The objective of this study was to determine how the application of 24-epibrassinolide (EBR), a brassinosteroid analog, could regulate root growth and tolerance to cadmium (Cd) stress in Kentucky bluegrass. As a result, the number of lateral root primordia and total root length in the Cd-treated seedlings decreased by 33.1 % and 56.5 %, respectively. After the application of EBR, Cd accumulation in roots and leaves, and the negative effect of Cd on root growth were reduced under Cd stress. Additionally, the expression of the brassinosteroid signaling gene PpBRI1 was significantly upregulated by exogenous EBR. Moreover, exogenous EBR upregulated the expression of genes encoding antioxidant enzymes and improved the activity of antioxidant enzymes, thereby reduced oxidative stress in roots. Finally, targeted hormonomics analysis highlighted the utility of the application of EBR to alleviate the effect of Cd on the reduction in auxin (IAA) content and the increase in ethylene (ACC) content. These were known to be associated with the upregulation in the expression of auxin biosynthesis gene PpYUCCA1 and downregulation in the expression of ethylene biosynthesis gene PpACO1 in the roots treated with Cd stress. Overall, the application of EBR alleviated Cd-induced oxidative stress in addition to improving root elongation and lateral root growth crosstalk with auxin and ethylene in Kentucky bluegrass subjected to Cd stress. This study further highlights the potential role of brassinosteroids in improving the efficiency of phytoremediation for Cd-contaminated soils.

The brassinosteroid biosynthesis gene TaD11-2A controls grain size and its elite haplotype improves wheat grain yields

TaD11-2A affects grain size and root length and its natural variations are associated with significant differences in yield-related traits in wheat. Brassinosteroids (BRs) control many important agronomic traits and therefore the manipulation of BR components could improve crop productivity and performance. However, the potential effects of BR-related genes on yield-related traits and stress tolerance in wheat (Triticum aestivum L.) remain poorly understood. Here, we identified TaD11 genes in wheat (rice D11 orthologs) that encoded enzymes involved in BR biosynthesis. TaD11 genes were highly expressed in roots (Zadoks scale: Z11) and grains (Z75), while expression was significantly suppressed by exogenous BR (24-epiBL). Ectopic expression of TaD11-2A rescued the abnormal panicle structure and plant height (PH) of the clustered primary branch 1 (cpb1) mutant, and also increased endogenous BR levels, resulting in improved grain yields and grain quality in rice. The tad11-2a-1 mutant displayed dwarfism, smaller grains, sensitivity to 24-epiBL, and reduced endogenous BR contents. Natural variations in TaD11-2A were associated with significant differences in yield-related traits, including PH, grain width, 1000-grain weight, and grain yield per plant, and its favorable haplotype, TaD11-2A-HapI was subjected to positive selection during wheat breeding. Additionally, TaD11-2A influenced root length and salt tolerance in rice and wheat at seedling stages. These results indicated the important role of BR TaD11 biosynthetic genes in controlling grain size and root length, and also highlighted their potential in the molecular biological analysis of wheat.

In-Silico Study of Brassinosteroid Signaling Genes in Rice Provides Insight Into Mechanisms Which Regulate Their Expression

Brassinosteroids (BRs) regulate a diverse spectrum of processes during plant growth and development and modulate plant physiology in response to environmental fluctuations and stress factors. Thus, the BR signaling regulators have the potential to be targeted for gene editing to optimize the architecture of plants and make them more resilient to environmental stress. Our understanding of the BR signaling mechanism in monocot crop species is limited compared to our knowledge of this process accumulated in the model dicot species - Arabidopsis thaliana. A deeper understanding of the BR signaling and response during plant growth and adaptation to continually changing environmental conditions will provide insight into mechanisms that govern the coordinated expression of the BR signaling genes in rice (Oryza sativa) which is a model for cereal crops. Therefore, in this study a comprehensive and detailed in silico analysis of promoter sequences of rice BR signaling genes was performed. Moreover, expression profiles of these genes during various developmental stages and reactions to several stress conditions were analyzed. Additionally, a model of interactions between the encoded proteins was also established. The obtained results revealed that promoters of the 39 BR signaling genes are involved in various regulatory mechanisms and interdependent processes that influence growth, development, and stress response in rice. Different transcription factor-binding sites and cis-regulatory elements in the gene promoters were identified which are involved in regulation of the genes’ expression during plant development and reactions to stress conditions. The in-silico analysis of BR signaling genes in O. sativa provides information about mechanisms which regulate the coordinated expression of these genes during rice development and in response to other phytohormones and environmental factors. Since rice is both an important crop and the model species for other cereals, this information may be important for understanding the regulatory mechanisms that modulate the BR signaling in monocot species. It can also provide new ways for the plant genetic engineering technology by providing novel potential targets, either cis-elements or transcriptional factors, to create elite genotypes with desirable traits.

Plant Salinity Stress Response and Nano-Enabled Plant Salt Tolerance

The area of salinized land is gradually expanding cross the globe. Salt stress seriously reduces the yield and quality of crops and endangers food supply to meet the demand of the increased population. The mechanisms underlying nano-enabled plant tolerance were discussed, including (1) maintaining ROS homeostasis, (2) improving plant's ability to exclude Na+ and to retain K+, (3) improving the production of nitric oxide, (4) increasing α-amylase activities to increase soluble sugar content, and (5) decreasing lipoxygenase activities to reduce membrane oxidative damage. The possible commonly employed mechanisms such as alleviating oxidative stress damage and maintaining ion homeostasis were highlighted. Further, the possible role of phytohormones and the molecular mechanisms in nano-enabled plant salt tolerance were discussed. Overall, this review paper aims to help the researchers from different field such as plant science and nanoscience to better understand possible new approaches to address salinity issues in agriculture.

Genome-wide identification of Gramineae histone modification genes and their potential roles in regulating wheat and maize growth and stress responses

BACKGROUND

In plants, histone modification (HM) genes participate in various developmental and defense processes. Gramineae plants (e.g., Triticum aestivum, Hordeum vulgare, Sorghum bicolor, Setaria italica, Setaria viridis, and Zea mays) are important crop species worldwide. However, little information on HM genes is in Gramineae species.

RESULTS

Here, we identified 245 TaHMs, 72 HvHMs, 84 SbHMs, 93 SvHMs, 90 SiHMs, and 90 ZmHMs in the above six Gramineae species, respectively. Detailed information on their chromosome locations, conserved domains, phylogenetic trees, synteny, promoter elements, and gene structures were determined. Among the HMs, most motifs were conserved, but several unique motifs were also identified. Our results also suggested that gene and genome duplications potentially impacted the evolution and expansion of HMs in wheat. The number of orthologous gene pairs between rice (Oryza sativa) and each Gramineae species was much greater than that between Arabidopsis and each Gramineae species, indicating that the dicotyledons shared common ancestors. Moreover, all identified HM gene pairs likely underwent purifying selection based on to their non-synonymous (Ka)/synonymous (Ks) nucleotide substitutions. Using published transcriptome data, changes in TaHM gene expression in developing wheat grains treated with brassinosteroid, brassinazole, or activated charcoal were investigated. In addition, the transcription models of ZmHMs in developing maize seeds and after gibberellin treatment were also identified. We also examined plant stress responses and found that heat, drought, salt, insect feeding, nitrogen, and cadmium stress influenced many TaHMs, and drought altered the expression of several ZmHMs. Thus, these findings indicate their important functions in plant growth and stress adaptations.

CONCLUSIONS

Based on a comprehensive analysis of Gramineae HMs, we found that TaHMs play potential roles in grain development, brassinosteroid- and brassinazole-mediated root growth, activated charcoal-mediated root and leaf growth, and biotic and abiotic adaptations. Furthermore, ZmHMs likely participate in seed development, gibberellin-mediated leaf growth, and drought adaptation.

Wheat Type One Protein Phosphatase Participates in the Brassinosteroid Control of Root Growth via Activation of BES1

Brassinosteroids (BRs) play key roles in diverse plant growth processes through a complex signaling pathway. Components orchestrating the BR signaling pathway include receptors such as kinases, transcription factors, protein kinases and phosphatases. The proper functioning of the receptor kinase BRI1 and the transcription factors BES1/BZR1 depends on their dephosphorylation by type 2A protein phosphatases (PP2A). In this work, we report that an additional phosphatase family, type one protein phosphatases (PP1), contributes to the regulation of the BR signaling pathway. Co-immunoprecipitation and BiFC experiments performed in Arabidopsis plants overexpressing durum wheat TdPP1 showed that TdPP1 interacts with dephosphorylated BES1, but not with the BRI1 receptor. Higher levels of dephosphorylated, active BES1 were observed in these transgenic lines upon BR treatment, indicating that TdPP1 modifies the BR signaling pathway by activating BES1. Moreover, ectopic expression of durum wheat TdPP1 lead to an enhanced growth of primary roots in comparison to wild-type plants in presence of BR. This phenotype corroborates with a down-regulation of the BR-regulated genes CPD and DWF4. These data suggest a role of PP1 in fine-tuning BR-driven responses, most likely via the control of the phosphorylation status of BES1.

Transcriptomic Study for Identification of Major Nitrogen Stress Responsive Genes in Australian Bread Wheat Cultivars

High nitrogen use efficiency (NUE) in bread wheat is pivotal to sustain high productivity. Knowledge about the physiological and transcriptomic changes that regulate NUE, in particular how plants cope with nitrogen (N) stress during flowering and the grain filling period, is crucial in achieving high NUE. Nitrogen response is differentially manifested in different tissues and shows significant genetic variability. A comparative transcriptome study was carried out using RNA-seq analysis to investigate the effect of nitrogen levels on gene expression at 0 days post anthesis (0 DPA) and 10 DPA in second leaf and grain tissues of three Australian wheat (Triticum aestivum) varieties that were known to have varying NUEs. A total of 12,344 differentially expressed genes (DEGs) were identified under nitrogen stress where down-regulated DEGs were predominantly associated with carbohydrate metabolic process, photosynthesis, light-harvesting, and defense response, whereas the up-regulated DEGs were associated with nucleotide metabolism, proteolysis, and transmembrane transport under nitrogen stress. Protein–protein interaction and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis further revealed that highly interacted down-regulated DEGs were involved in light-harvesting and photosynthesis, and up-regulated DEGs were mostly involved in steroid biosynthesis under N stress. The common down-regulated genes across the cultivars included photosystem II 10 kDa polypeptide family proteins, plant protein 1589 of uncharacterized protein function, etc., whereas common up-regulated genes included glutamate carboxypeptidase 2, placenta-specific8 (PLAC8) family protein, and a sulfate transporter. On the other hand, high NUE cultivar Mace responded to nitrogen stress by down-regulation of a stress-related gene annotated as beta-1,3-endoglucanase and pathogenesis-related protein (PR-4, PR-1) and up-regulation of MYB/SANT domain-containing RADIALIS (RAD)-like transcription factors. The medium NUE cultivar Spitfire and low NUE cultivar Volcani demonstrated strong down-regulation of Photosystem II 10 kDa polypeptide family protein and predominant up-regulation of 11S globulin seed storage protein 2 and protein transport protein Sec61 subunit gamma. In grain tissue, most of the DEGs were related to nitrogen metabolism and proteolysis. The DEGs with high abundance in high NUE cultivar can be good candidates to develop nitrogen stress-tolerant variety with improved NUE.