Genome-wide identification and characterization of WOX genes in Cucumis sativus

Insights into cucumber (Cucumis sativus) genetics: Genome-wide discovery and computational analysis of the Calreticulin Domain-Encoding gene (CDEG) family

Cucumber is an essential vegetable crop throughout the world. Cucumber development is vital for accomplishing both quality and productivity requirements. Meanwhile, numerous factors have resulted in substantial cucumber losses. However, the calreticulin domain-encoding genes (CDEGs) in cucumber were not well-characterized and had little function. In the genome-wide association study (GWAS), we recognized and characterized the CDEGs in Cucumis sativus (cucumber). Through a comprehensive study of C. sativus, our research has unveiled the presence of three unique genes, denoted as CsCRTb, CsCRT3, and CsCNX1, unevenly distributed on three chromosomes in the genome of C. sativus. In accordance to the phylogenetic investigation, these genes may be categorized into three subfamilies. Based on the resemblance with AtCDE genes, we reorganized the all CsCDE genes in accordance with international nomenclature. The expression analysis and cis-acting components revealed that each of CsCDE gene promoter region enclosed number of cis-elements connected with hormone and stress response. According to subcellular localization studies demonstrated that, they were found in deferent locations of the cell such as endoplasmic reticulum, plasma membrane, golgi apparatus, and vacuole, according to subcellular localization studies. Chromosomal distribution analysis and synteny analysis demonstrated the probability of segmental or tandem duplications within the cucumber CDEG gene family. Additionally, miRNAs displayed diverse modes of action, including mRNA cleavage and translational inhibition. We used the RNA seq data to analyze the expression of CDEG genes in response to cold stress and also improved cold tolerance, which was brought on by treating cucumber plants to an exogenous chitosan oligosaccharide spray. Our investigation revealed that these genes responded to this stress in a variety of ways, demonstrating that they may adapt quickly to environmental changes in cucumber plants. This study provides a base for further understanding in reference to CDE gene family and reveals that genes play significant functions in cucumber stress responses.

A Comprehensive Identification and Expression Analysis of the WUSCHEL Homeobox-Containing Protein Family Reveals Their Special Role in Development and Abiotic Stress Response in Zea mays L

Maize is an important food and cash crop worldwide. The WUSCHEL (WUS)-related homeobox (WOX) transcription factor (TF) family plays a significant role in the development process and the response to abiotic stress of plants. However, few studies have been reported on the function of WOX genes in maize. This work, utilizing the latest maize B73 reference genome, results in the identification of 22 putative ZmWOX gene family members. Except for chromosome 5, the 22 ZmWOX genes were homogeneously distributed on the other nine chromosomes and showed three tandem duplication and 10 segmental duplication events. Based on phylogenetic characteristics, ZmWOXs are divided into three clades (e.g., WUS, intermediate, and ancient groups), and the majority of ZmWOXs in same group display similar gene and protein structures. Cross-species collinearity results indicated that some WOX genes might be evolutionarily conservative. The promoter region of ZmWOX family members is enriched in light, plant growth/hormone, and abiotic stress-responsive elements. Tissue-specific expression evaluation showed that ZmWOX genes might play a significant role in the occurrence of maize reproductive organs. Transcriptome data and RT-qPCR analysis further showed that six ZmWOX genes (e.g., ZmWOX1, 4, 6, 13, 16, and 18) were positively or negatively modulated by temperature, salt, and waterlogging stresses. Moreover, two ZmWOXs, ZmWOX1 and ZmWOX18, both were upregulated by abiotic stress. ZmWOX18 was localized in the nucleus and had transactivation activities, while ZmWOX1 was localized in both the cytoplasm and nucleus, without transactivation activity. Overall, this work offers new perspectives on the evolutionary relationships of ZmWOX genes and might provide a resource for further detecting the biological functions of ZmWOXs.

Pan-genome Analysis of WOX Gene Family and Function Exploration of CsWOX9 in Cucumber

Cucumber is an economically important vegetable crop, and the warts (composed of spines and Tubercules) of cucumber fruit are an important quality trait that influences its commercial value. WOX transcription factors are known to have pivotal roles in regulating various aspects of plant growth and development, but their studies in cucumber are limited. Here, genome-wide identification of cucumber WOX genes was performed using the pan-genome analysis of 12 cucumber varieties. Our findings revealed diverse CsWOX genes in different cucumber varieties, with variations observed in protein sequences and lengths, gene structure, and conserved protein domains, possibly resulting from the divergent evolution of CsWOX genes as they adapt to diverse cultivation and environmental conditions. Expression profiles of the CsWOX genes demonstrated that CsWOX9 was significantly expressed in unexpanded ovaries, especially in the epidermis. Additionally, analysis of the CsWOX9 promoter revealed two binding sites for the C2H2 zinc finger protein. We successfully executed a yeast one-hybrid assay (Y1H) and a dual-luciferase (LUC) transaction assay to demonstrate that CsWOX9 can be transcriptionally activated by the C2H2 zinc finger protein Tu, which is crucial for fruit Tubercule formation in cucumber. Overall, our results indicated that CsWOX9 is a key component of the molecular network that regulates wart formation in cucumber fruits, and provide further insight into the function of CsWOX genes in cucumber.

Identification of WUSCHEL-related homeobox gene and truncated small peptides in transformation efficiency improvement in Eucalyptus

BACKGROUND

The WUSCHEL-related Homeobox (WOX) genes, which encode plant-specific homeobox (HB) transcription factors, play crucial roles in regulating plant growth and development. However, the functions of WOX genes are little known in Eucalyptus, one of the fastest-growing tree resources with considerable widespread cultivation worldwide.

RESULTS

A total of nine WOX genes named EgWOX1-EgWOX9 were retrieved and designated from Eucalyptus grandis. From the three divided clades marked as Modern/WUS, Intermediate and Ancient, the largest group Modern/WUS (6 EgWOXs) contains a specific domain with 8 amino acids: TLQLFPLR. The collinearity, cis-regulatory elements, protein-protein interaction network and gene expression analysis reveal that the WUS proteins in E. grandis involve in regulating meristems development and regeneration. Furthermore, by externally adding of truncated peptides isolated from WUS specific domain, the transformation efficiency in E. urophylla × E. grandis DH32-29 was significant enhanced. The transcriptomics data further reveals that the use of small peptides activates metabolism pathways such as starch and sucrose metabolism, phenylpropanoid biosynthesis and flavonoid biosynthesis.

CONCLUSIONS

Peptides isolated from WUS protein can be utilized to enhance the transformation efficiency in Eucalyptus, thereby contributing to the high-efficiency breeding of Eucalyptus.

NnWOX1-1, NnWOX4-3, and NnWOX5-1 of lotus (Nelumbo nucifera Gaertn)promote root formation and enhance stress tolerance in transgenic Arabidopsis thaliana

BACKGROUND

Adventitious roots (ARs) represent an important organ system for water and nutrient uptake in lotus plants because of degeneration of the principal root. The WUSCHEL-related homeobox (WOX) gene regulates plant development and growth by affecting the expression of several other genes. In this study, three WOX genes, NnWOX1-1, NnWOX4-3, and NnWOX5-1, were isolated and their functions were assessed in Arabidopsis plants.

RESULTS

The full lengths of NnWOX1-1, NnWOX4-3, and NnWOX5-1 were 1038, 645, and 558 bp, encoding 362, 214, and 185 amino acid residues, respectively. Phylogenetic analysis classified NnWOX1-1 and NnWOX4-3 encoding proteins into one group, and NnWOX5-1 and MnWOX5 encoding proteins exhibited strong genetic relationships. The three genes were induced by sucrose and indoleacetic acid (IAA) and exhibited organ-specific expression characteristics. In addition to improving root growth and salt tolerance, NnWOX1-1 and NnWOX4-3 promoted stem development in transgenic Arabidopsis plants. A total of 751, 594, and 541 genes, including 19, 19, and 13 respective genes related to ethylene and IAA metabolism and responses, were enhanced in NnWOX1-1, NnWOX4-3, and NnWOX5-1 transgenic plants, respectively. Further analysis showed that ethylene production rates in transgenic plants increased, whereas IAA, peroxidase, and lignin content did not significantly change. Exogenous application of ethephon on lotus seedlings promoted AR formation and dramatically increased the fresh and dry weights of the plants.

CONCLUSIONS

NnWOX1-1, NnWOX4-3, and NnWOX5-1 influence root formation, stem development, and stress adaptation in transgenic Arabidopsis plants by affecting the transcription of multiple genes. Among these, changes in gene expression involving ethylene metabolism and responses likely critically affect the development of Arabidopsis plants. In addition, ethylene may represent an important factor affecting AR formation in lotus seedlings.

Comprehensive in silico analysis of the underutilized crop tef (Eragrostis tef (Zucc.) Trotter) genome reveals drought tolerance signatures

BACKGROUND

Tef (Eragrostis tef) is a C4 plant known for its tiny, nutritious, and gluten-free grains. It contains higher levels of protein, vitamins, and essential minerals like calcium (Ca), iron (Fe), copper (Cu), and zinc (Zn) than common cereals. Tef is cultivated in diverse ecological zones under diverse climatic conditions. Studies have shown that tef has great diversity in withstanding environmental challenges such as drought. Drought is a major abiotic stress severely affecting crop productivity and becoming a bottleneck to global food security. Here, we used in silico-based functional genomic analysis to identify drought-responsive genes in tef and validated their expression using quantitative RT-PCR.

RESULTS

We identified about 729 drought-responsive genes so far reported in six crop plants, including rice, wheat, maize, barley, sorghum, pearl millet, and the model plant Arabidopsis, and reported 20 genes having high-level of GO terms related to drought, and significantly enriched in several biological and molecular function categories. These genes were found to play diverse roles, including water and fluid transport, resistance to high salt, cold, and drought stress, abscisic acid (ABA) signaling, de novo DNA methylation, and transcriptional regulation in tef and other crops. Our analysis revealed substantial differences in the conserved domains of some tef genes from well-studied rice orthologs. We further analyzed the expression of sixteen tef orthologs using quantitative RT-PCR in response to PEG-induced osmotic stress.

CONCLUSIONS

The findings showed differential regulation of some drought-responsive genes in shoots, roots, or both tissues. Hence, the genes identified in this study may be promising candidates for trait improvement in crops via transgenic or gene-editing technologies.

Characterization and expression profiles of WUSCHEL-related homeobox (WOX) gene family in cultivated alfalfa (Medicago sativa L.)

The WUSCHEL-related homeobox (WOX) family members are plant-specific transcriptional factors, which function in meristem maintenance, embryogenesis, lateral organ development, as well as abiotic stress tolerance. In this study, 14 MsWOX transcription factors were identified and comprehensively analyzed in the cultivated alfalfa cv. Zhongmu No.1. Overall, 14 putative MsWOX members containing conserved structural regions were clustered into three clades according to phylogenetic analysis. Specific expression patterns of MsWOXs in different tissues at different levels indicated that the MsWOX genes play various roles in alfalfa. MsWUS, MsWOX3, MsWOX9, and MsWOX13-1 from the three subclades were localized in the nucleus, among which, MsWUS and MsWOX13-1 exhibited strong self-activations in yeast. In addition, various cis-acting elements related to hormone responses, plant growth, and stress responses were identified in the 3.0 kb promoter regions of MsWOXs. Expression detection of separated shoots and roots under hormones including auxin, cytokinin, GA, and ABA, as well as drought and cold stresses, showed that MsWOX genes respond to different hormones and abiotic stress treatments. Furthermore, transcript abundance of MsWOX3, and MsWOX13-2 were significantly increased after rhizobia inoculation. This study presented comprehensive data on MsWOX transcription factors and provided valuable insights into further studies of their roles in developmental processes and abiotic stress responses in alfalfa.

Genome-Wide Identification and Characterization Analysis of WUSCHEL-Related Homeobox Family in Melon (Cucumis melo L.)

WUSCHEL-related homeobox (WOX) proteins are very important in controlling plant development and stress responses. However, the WOX family members and their role in response to abiotic stresses are largely unknown in melon (Cucumis melo L.). In this study, 11 WOX (CmWOX) transcript factors with conserved WUS and homeobox motif were identified and characterized, and subdivided into modern clade, ancient clade and intermediate clade based on bioinformatic and phylogenetic analysis. Evolutionary analysis revealed that the CmWOX family showed protein variations in Arabidopsis, tomato, cucumber, melon and rice. Alignment of protein sequences uncovered that all CmWOXs had the typical homeodomain, which consisted of conserved amino acids. Cis-element analysis showed that CmWOX genes may response to abiotic stress. RNA-seq and qRT-PCR results further revealed that the expression of partially CmWOX genes are associated with cold and drought. CmWOX13a and CmWOX13b were constitutively expressed under abiotic stresses, CmWOX4 may play a role in abiotic processes during plant development. Taken together, this study offers new perspectives on the CmWOX family's interaction and provides the framework for research on the molecular functions of CmWOX genes.

Genome-wide identification and molecular characterization of CRK gene family in cucumber (Cucumis sativus L.) under cold stress and sclerotium rolfsii infection

BACKGROUND

The plant cysteine-rich receptor-like kinases (CRKs) are a large family having multiple roles, including defense responses under both biotic and abiotic stress. However, the CRK family in cucumbers (Cucumis sativus L.) has been explored to a limited extent. In this study, a genome-wide characterization of the CRK family has been performed to investigate the structural and functional attributes of the cucumber CRKs under cold and fungal pathogen stress.

RESULTS

A total of 15 C. sativus CRKs (CsCRKs) have been characterized in the cucumber genome. Chromosome mapping of the CsCRKs revealed that 15 genes are distributed in cucumber chromosomes. Additionally, the gene duplication analysis of the CsCRKs yielded information on their divergence and expansion in cucumbers. Phylogenetic analysis divided the CsCRKs into two clades along with other plant CRKs. Functional predictions of the CsCRKs suggested their role in signaling and defense response in cucumbers. The expression analysis of the CsCRKs by using transcriptome data and via qRT-PCR indicated their involvement in both biotic and abiotic stress responses. Under the cucumber neck rot pathogen, Sclerotium rolfsii infection, multiple CsCRKs exhibited induced expressions at early, late, and both stages. Finally, the protein interaction network prediction results identified some key possible interacting partners of the CsCRKs in regulating cucumber physiological processes.

CONCLUSIONS

The results of this study identified and characterized the CRK gene family in cucumbers. Functional predictions and validation via expression analysis confirmed the involvement of the CsCRKs in cucumber defense response, especially against S. rolfsii. Moreover, current findings provide better insights into the cucumber CRKs and their involvement in defense responses.

Induction of Somatic Embryogenesis in Plants: Different Players and Focus on WUSCHEL and WUS-RELATED HOMEOBOX (WOX) Transcription Factors

In plants, other cells can express totipotency in addition to the zygote, thus resulting in embryo differentiation; this appears evident in apomictic and epiphyllous plants. According to Haberlandt's theory, all plant cells can regenerate a complete plant if the nucleus and the membrane system are intact. In fact, under in vitro conditions, ectopic embryos and adventitious shoots can develop from many organs of the mature plant body. We are beginning to understand how determination processes are regulated and how cell specialization occurs. However, we still need to unravel the mechanisms whereby a cell interprets its position, decides its fate, and communicates it to others. The induction of somatic embryogenesis might be based on a plant growth regulator signal (auxin) to determine an appropriate cellular environment and other factors, including stress and ectopic expression of embryo or meristem identity transcription factors (TFs). Still, we are far from having a complete view of the regulatory genes, their target genes, and their action hierarchy. As in animals, epigenetic reprogramming also plays an essential role in re-establishing the competence of differentiated cells to undergo somatic embryogenesis. Herein, we describe the functions of WUSCHEL-RELATED HOMEOBOX (WOX) transcription factors in regulating the differentiation-dedifferentiation cell process and in the developmental phase of in vitro regenerated adventitious structures.

Genome-Wide Identification and Expression Analysis of the NAC Gene Family in Kandelia obovata, a Typical Mangrove Plant

The NAC (NAM, ATAF1/2, and CUC2) gene family, one of the largest transcription factor families in plants, acts as positive or negative regulators in plant response and adaption to various environmental stresses, including cold stress. Multiple reports on the functional characterization of NAC genes in Arabidopsis thaliana and other plants are available. However, the function of the NAC genes in the typical woody mangrove (Kandelia obovata) remains poorly understood. Here, a comprehensive analysis of NAC genes in K. obovata was performed with a pluri-disciplinary approach including bioinformatic and molecular analyses. We retrieved a contracted NAC family with 68 genes from the K. obovata genome, which were unevenly distributed in the chromosomes and classified into ten classes. These KoNAC genes were differentially and preferentially expressed in different organs, among which, twelve up-regulated and one down-regulated KoNAC genes were identified. Several stress-related cis-regulatory elements, such as LTR (low-temperature response), STRE (stress response element), ABRE (abscisic acid response element), and WUN (wound-responsive element), were identified in the promoter regions of these 13 KoNAC genes. The expression patterns of five selected KoNAC genes (KoNAC6, KoNAC15, KoNAC20, KoNAC38, and KoNAC51) were confirmed by qRT-PCR under cold treatment. These results strongly implied the putative important roles of KoNAC genes in response to chilling and other stresses. Collectively, our findings provide valuable information for further investigations on the function of KoNAC genes.

Research Progress on the Leaf Morphology, Fruit Development and Plant Architecture of the Cucumber

Cucumber (Cucumis sativus L.) is an annual climbing herb that belongs to the Cucurbitaceae family and is one of the most important economic crops in the world. The breeding of cucumber varieties with excellent agronomic characteristics has gained more attention in recent years. The size and shape of the leaves or fruit and the plant architecture are important agronomic traits that influence crop management and productivity, thus determining the crop yields and consumer preferences. The growth of the plant is precisely regulated by both environmental stimuli and internal signals. Although significant progress has been made in understanding the plant morphological regulation of Arabidopsis, rice, and maize, our understanding of the control mechanisms of the growth and development of cucumber is still limited. This paper reviews the regulation of phytohormones in plant growth and expounds the latest progress in research regarding the genetic regulation pathways in leaf development, fruit size and shape, branching, and plant type in cucumber, so as to provide a theoretical basis for improving cucumber productivity and cultivation efficiency.

Genome-Wide Identification and Comparative Analysis of WOX Genes in Four Euphorbiaceae Species and Their Expression Patterns in Jatropha curcas

The WUSCHEL-related homeobox (WOX) proteins are widely distributed in plants and play important regulatory roles in growth and development processes such as embryonic development and organ development. Here, series of bioinformatics methods were utilized to unravel the structural basis and genetic hierarchy of WOX genes, followed by regulation of the WOX genes in four Euphorbiaceae species. A genome-wide survey identified 59 WOX genes in Hevea brasiliensis (H. brasiliensis: 20 genes), Jatropha curcas (J. curcas: 10 genes), Manihot esculenta (M. esculenta: 18 genes), and Ricinus communis (R. communis: 11 genes). The phylogenetic analysis revealed that these WOX members could be clustered into three close proximal clades, such as namely ancient, intermediate and modern/WUS clades. In addition, gene structures and conserved motif analyses further validated that the WOX genes were conserved within each phylogenetic clade. These results suggested the relationships among WOX members in the four Euphorbiaceae species. We found that WOX genes in H. brasiliensis and M. esculenta exhibit close genetic relationship with J. curcas and R. communis. Additionally, the presence of various cis-acting regulatory elements in the promoter of J. curcas WOX genes (JcWOXs) reflected distinct functions. These speculations were further validated with the differential expression profiles of various JcWOXs in seeds, reflecting the importance of two JcWOX genes (JcWOX6 and JcWOX13) during plant growth and development. Our quantitative real-time PCR (qRT-PCR) analysis demonstrated that the JcWOX11 gene plays an indispensable role in regulating plant callus. Taken together, the present study reports the comprehensive characteristics and relationships of WOX genes in four Euphorbiaceae species, providing new insights into their characterization.

PtrWOX13A Promotes Wood Formation and Bioactive Gibberellins Biosynthesis in Populus trichocarpa

WUSCHEL-related homeobox (WOX) genes are plant-specific transcription factors (TFs) involved in multiple processes of plant development. However, there have hitherto no studies on the WOX TFs involved in secondary cell wall (SCW) formation been reported. In this study, we identified a Populus trichocarpa WOX gene, PtrWOX13A, which was predominantly expressed in SCW, and then characterized its functions through generating PtrWOX13A overexpression poplar transgenic lines; these lines exhibited not only significantly enhanced growth potential, but also remarkably increased SCW thicknesses, fiber lengths, and lignin and hemicellulose contents. However, no obvious change in cellulose content was observed. We revealed that PtrWOX13A directly activated its target genes through binding to two cis-elements, ATTGATTG and TTAATSS, in their promoter regions. The fact that PtrWOX13A responded to the exogenous GAs implies that it is responsive to GA homeostasis caused by GA inactivation and activation genes (e.g., PtrGA20ox4, PtrGA2ox1, and PtrGA3ox1), which were regulated by PtrWOX13A directly or indirectly. Since the master switch gene of SCW formation, PtrWND6A, and lignin biosynthesis regulator, MYB28, significantly increased in PtrWOX13A transgenic lines, we proposed that PtrWOX13A, as a higher hierarchy TF, participated in SCW formation through controlling the genes that are components of the known hierarchical transcription regulation network of poplar SCW formation, and simultaneously triggering a gibberellin-mediated signaling cascade. The discovery of PtrWOX13A predominantly expressed in SCW and its regulatory functions in the poplar wood formation has important implications for improving the wood quality of trees via genetic engineering.

The genome-wide characterization of WOX gene family in Phaseolus vulgaris L. during salt stress

The WUSCHEL-Related Homeobox (WOX) family is a type of homeobox transcription factor superfamily and its members perform many functions ranging from plant embryonic growth to organ formation in plants. Although the WOX proteins have been identified and characterized in many plant species, genome-wide identification and characterization of WOX proteins in the Phaseolus vulgaris genome has been performed for the first time in this study. Accordingly, 18 WOX proteins were identified using bioinformatics tools and biochemical/physicochemical properties of these proteins were investigated. Phvul-WOX genes were found to be categorized into three major phylogenetic groups according to the phylogenetic analysis and a total of five segmental duplication events were detected after duplication analysis. Moreover, the Phvul-WOX genes were found to be expressed in different plant tissues at different levels and some stress-related miRNAs have been found to target the Phvul-WOX genes based on miRNA analysis. Additionaly, MDA content, total protein level and catalase enzyme activity analyses were conducted in two P. vulgaris cultivars namely Yakutiye cv. and Zulbiye cv. subjected to 150 mM salt stress. Next, these cultivars were used for screening the expression levels of Phvul-WOX-1, Phvul-WOX-9, Phvul-WOX-11, Phvul-WOX-15 and Phvul-WOX-16 genes in response to salt stress. The insights gained from this study may be of assistance to the researchers who work in this area.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01208-1.

In silico identification, characterization expression profile of WUSCHEL-Related Homeobox (WOX) gene family in two species of kiwifruit

The WUSCHEL (WUS)-related homeobox (WOX) gene family is a class of plant-specific transcriptional factors and plays a crucial role in forming the shoot apical meristem and embryonic development, stem cell maintenance, and various other developmental processes. However, systematic identification and characterization of the kiwifruit WOX gene family have not been studied. This study identified 17 and 10 WOX genes in A. chinensis (Ac) and A. eriantha (Ae) genomes, respectively. Phylogenetic analysis classified kiwifruit WOX genes from two species into three clades. Analysis of phylogenetics, synteny patterns, and selection pressure inferred that WOX gene families in Ac and Ae had undergone different evolutionary patterns after whole-genome duplication (WGD) events, causing differences in WOX gene number and distribution. Ten conserved motifs were identified in the kiwifruit WOX genes, and motif architectures of WOXs belonging to different clades highly diverged. The cis-element analysis and expression profiles investigation indicated the functional differentiation of WOX genes and identified the potential WOXs in response to stresses. Our results provided insight into general characters, evolutionary patterns, and functional diversity of kiwifruit WOXs.