Glycogen synthase kinases in model and crop plants - From negative regulators of brassinosteroid signaling to multifaceted hubs of various signaling pathways and modulators of plant reproduction and yield

The brassinosteroid-mediated Camellia sinensis synthase kinase1 and Camellia sinensis sumo conjugation enzyme1 module positively regulates the cold tolerance of tea plant

Plant glycogen synthase kinase 3 (GSK3) is involved in germinal development and stress response. In the present study, 15 GSK3 members were identified in tea plants and categorised into four subfamilies. During brassinosteroid (BR)-mediated cold stress, the expression levels of the Camellia sinensis synthase kinase1(CsSK1) gene was significantly down-regulated. This gene is highly homologous to the gene encoding BRASSINOSTEROID INSENSITIVE (BIN2) in Arabidopsis (Arabidopsis thaliana). These results suggest that CsSK1 is a candidate gene involved in BR-mediated cold stress in tea plants. Overexpression of the CsSK1 gene in A. thaliana reduced the survival rate of plants at low temperatures, thereby weakening cold tolerance. However, after silencing the CsSK1 in tea plants, cold tolerance was enhanced. In this study, we determined that the protein Camellia sinensis sumo conjugation enzyme1 (CsSCE1) interacts with CsSK1. Silencing of CsSCE1 weakened the cold tolerance of tea plants, indicating that CsSCE1 positively regulates plant cold resistance. Additionally, silencing of CsSCE1 enhanced the expression of CsSK1; similarly, the expression of CsSCE1 increased after CsSK1 was silenced. In summary, CsSK1 interacts with CsSCE1 and plays a negative regulatory role in cold tolerance in tea plants. This study provides new insights into the role of BRs in the regulation of cold tolerance in plants.

Genetic manipulations of brassinosteroid-related genes improve various agronomic traits and yield in cereals enabling new biotechnological revolution: Achievements and perspectives

Brassinosteroids (BRs) are steroid phytohormones which regulate various developmental and physiological processes throughout plant life cycle, from seed development and germination, up to modulation of reproduction and senescence. Importantly, mutants defective in the BR biosynthesis or response show various degree of plant height reduction (dwarfism or semi-dwarfism). This agronomic trait is of particular importance considering that in contrast to tall cereal varieties, semi-dwarf cereal plants are more tolerant to lodging which occurs during unfavorable weather conditions and constitutes a serious threat to plant reproduction and yield. Moreover, it was shown that the BR deficiency or insensitivity lead to erect stature of cereal plants what enables increase in planting density and yield. The valuable combinations of these traits make the BR-related mutants exceptional alternatives in breeding programs. Noteworthy, BRs play a noticeable role in regulation of grain/kernel shape and size. Therefore, these crucial agronomic traits may be manipulated specifically in BR-dependent manner. Importantly, the semi-dwarf mutants have been successfully introduced into cereal breeding programs in the past, and new semi-dwarf mutants developed through application of gene editing approach have been recently reported as promising alternatives for development of novel, high-yielding cereal cultivars. This review presents a comprehensive description of genetic manipulations of the BR-related genes aimed at improvements of various agronomic traits in the major cereal crops - rice, wheat, maize, and barley. These improvements may be achieved through application of panicle- or grain-specific promoters, overexpression or gain-of-function approaches, gene silencing, and targeted gene editing.

Take a deep BReath: Manipulating brassinosteroid homeostasis helps cereals adapt to environmental stress

Global climate change leads to the increased occurrence of environmental stress (including drought and heat stress) during the vegetative and reproductive stages of cereal crop development. Thus, more attention should be given to developing new cereal cultivars with improved tolerance to environmental stress. However, during the development of new stress-tolerant cereal cultivars, the balance between improved stress responses (which occur at the expense of growth) and plant yield needs to be maintained. Thus, the urgent need for developing new cereal germplasm with improved stress tolerance could be fulfilled using semidwarf cereal mutants defective in brassinosteroid (BR) biosynthesis or signaling. BRs are steroid phytohormones that regulate various developmental and physiological processes throughout the plant life cycle. Mutants defective in BR biosynthesis or responses show reduced plant height (dwarfism or semi-dwarfism). Importantly, numerous reports indicate that genetic modification or biotechnological manipulation of BR biosynthesis or signaling genes in cereals such as rice (Oryza sativa), maize (Zea mays), wheat (Triticum aestivum), and barley (Hordeum vulgare), which are of crucial importance for global agriculture, may facilitate the development of cereal germplasm with improved stress tolerance. This review presents a comprehensive overview of the genetic manipulation of BR homeostasis in the above-mentioned cereal crops aimed at improving plant responses to various environmental stresses, such as drought, salinity, oxidative stress, thermal stress, and biotic stresses. We highlight target BR-related genes and the effects of genetic manipulation (gene editing, overexpression, and silencing or microRNA-mediated regulation) on plant adaptability to various stresses and provide future perspectives.

Genome-Wide Association Study and Prediction of Tassel Weight of Tropical Maize Germplasm in Multi-Parent Population

Tassel weight (TW) is a crucial agronomic trait that significantly affects pollen supply and grain yield development in maize breeding. To improve maize yield and develop new varieties, a comprehensive understanding of the genetic mechanisms underlying tassel weight is essential. In this study, tropical maize inbred lines, namely CML312, CML373, CML444, and YML46, were selected as female parents and crossed with the elite maize inbred line Ye107, which served as the common male parent, to develop a multi-parent population comprising four F8 recombinant inbred line (RIL) subpopulations. Using 6616 high-quality single nucleotide polymorphism (SNP) markers, we conducted genome-wide association analysis (GWAS) and genomic selection (GS) on 642 F8 RILs in four subpopulations across three different environments. Through GWAS, we identified 16 SNPs that were significantly associated with TW, encompassing two stable loci expressed across multiple environments. Furthermore, within the candidate regions of these SNPs, we discovered four novel candidate genes related to TW, namely Zm00001d044362, Zm00001d011048, Zm00001d011049, and Zm00001d031173 distributed on chromosomes 1, 3, and 8, which have not been previously reported. These genes are involved in processes such as signal transduction, growth and development, protein splicing, and pollen development, all of which play crucial roles in inflorescence meristem development, directly affecting TW. The co-localized SNP, S8_137379725, on chromosome 8 was situated within a 16.569 kb long terminal repeat retrotransposon (LTR-RT), located 22.819 kb upstream and 26.428 kb downstream of the candidate genes (Zm00001d011048 and Zm00001d011049). When comparing three distinct GS models, the BayesB model demonstrated the highest accuracy in predicting TW. This study establishes the theoretical foundation for future research into the genetic mechanisms underlying maize TW and the efficient breeding of high-yielding varieties with desired tassel weight through GS.

Analyses of genes encoding the Glycogen Synthase Kinases in rice and Arabidopsis reveal mechanisms which regulate their expression during development and responses to abiotic stresses

Plant Glycogen Synthase Kinases (GSKs) enable a crosstalk among the brassinosteroid signaling and phytohormonal- and stress-response pathways to regulate various physiological processes. Initial information about regulation of the GSK proteins' activity was obtained, however, mechanisms that modulate expression of the GSK genes during plant development and stress responses remain largely unknown. Taking into account the importance of the GSK proteins, combined with the lack of in-depth knowledge about modulation of their expression, research in this area may provide a significant insight into mechanisms regulating these aspects of plant biology. In the current study, a detailed analysis of the GSK promoters in rice and Arabidopsis was performed, including identification of the CpG/CpNpG islands, tandem repeats, cis-acting regulatory elements, conserved motifs, and transcription factor-binding sites. Moreover, characterization of expression profiles of the GSK genes in different tissues, organs and under various abiotic stress conditions was perfomed. Additionally, protein-protein interactions between products of the GSK genes were predicted. Results of this study provided intriguing information about these aspects and insight into various regulatory mechanisms that influence non-redundant and diverse functions of the GSK genes during development and stress responses.Therefore, they may constitute a reference for future research in other plant species.

Kinase POGSK-3β modulates fungal plant polysaccharide-degrading enzyme production and development

The filamentous fungus Penicillium oxalicum secretes integrative plant polysaccharide-degrading enzymes (PPDEs) applicable to biotechnology. Glycogen synthase kinase-3β (GSK-3β) mediates various cellular processes in eukaryotic cells, but the regulatory mechanisms of PPDE biosynthesis in filamentous fungi remain poorly understood. In this study, POGSK-3β (POX_c04478), a homolog of GSK-3β in P. oxalicum, was characterised using biochemical, microbiological and omics approaches. Knockdown of POGSK-3β in P. oxalicum using a copper-responsive promoter replacement system led to 53.5 - 63.6%, 79.0 - 92.8% and 76.8 - 94.7% decreases in the production of filter paper cellulase, soluble starch-degrading enzyme and raw starch-degrading enzyme, respectively, compared with the parental strain ΔKu70. POGSK-3β promoted mycelial growth and conidiation. Transcriptomic profiling and real-time quantitative reverse transcription PCR analyses revealed that POGSK-3β dynamically regulated the expression of genes encoding major PPDEs, as well as fungal development-associated genes. The results broadened our understanding of the regulatory functions of GKS-3β and provided a promising target for genetic engineering to improve PPDE production in filamentous fungi. KEY POINTS: • The roles of glycogen synthase kinase-3β were investigated in P. oxalicum. • POGSK-3β regulated PPDE production, mycelial growth and conidiation. • POGSK-3β controlled the expression of major PPDE genes and regulatory genes.

Regulatory network of GSK3-like kinases and their role in plant stress response

Glycogen synthase kinase 3 (GSK3) family members are evolutionally conserved Ser/Thr protein kinases in mammals and plants. In plants, the GSK3s function as signaling hubs to integrate the perception and transduction of diverse signals required for plant development. Despite their role in the regulation of plant growth and development, emerging research has shed light on their multilayer function in plant stress responses. Here we review recent advances in the regulatory network of GSK3s and the involvement of GSK3s in plant adaptation to various abiotic and biotic stresses. We also discuss the molecular mechanisms underlying how plants cope with environmental stresses through GSK3s-hormones crosstalk, a pivotal biochemical pathway in plant stress responses. We believe that our overview of the versatile physiological functions of GSK3s and underlined molecular mechanism of GSK3s in plant stress response will not only opens further research on this important topic but also provide opportunities for developing stress-resilient crops through the use of genetic engineering technology.

Plant Defense and Viral Counter-Defense during Plant-Geminivirus Interactions

Geminiviruses are the largest family of plant viruses that cause severe diseases and devastating yield losses of economically important crops worldwide. In response to geminivirus infection, plants have evolved ingenious defense mechanisms to diminish or eliminate invading viral pathogens. However, increasing evidence shows that geminiviruses can interfere with plant defense response and create a suitable cell environment by hijacking host plant machinery to achieve successful infections. In this review, we discuss recent findings about plant defense and viral counter-defense during plant-geminivirus interactions.