Genome-Wide Organization and Expression Profiling of the SBP-Box Gene Family in Chinese Jujube (Ziziphus jujuba Mill.)

Genome-wide identification and analysis of the evolution and expression pattern of the SBP gene family in two Chimonanthus species

BACKGROUND

Chimonanthus praecox and Chimonanthus salicifolius are closely related species that diverged approximately six million years ago. While both C. praecox and C. salicifolius could withstand brief periods of low temperatures of - 15 °C. Their flowering times are different, C. praecox blooms in early spring, whereas C. salicifolius blooms in autumn. The SBP-box (SQUAMOSA promoter-binding protein) is a plant-specific gene family that plays a crucial vital role in regulating plant flowering. Although extensively studied in various plants, the SBP gene family remains uncharacterized in Calycanthaceae.

METHODS AND RESULTS

We conducted genome-wide identification of SBP genes in both C. praecox and C. salicifolius and comprehensively characterized the chromosomal localization, gene structure, conserved motifs, and domains of the identified SBP genes. In total, 15 and 18 SBP genes were identified in C. praecox and C. salicifolius, respectively. According to phylogenetic analysis, the SBP genes from Arabidopsis, C. praecox, and C. salicifolius were clustered into eight groups. Analysis of the gene structure and conserved protein motifs showed that SBP proteins of the same subfamily have similar motif structures. The expression patterns of SBP genes were analyzed using transcriptome data. The results revealed that more than half of the genes exhibited lower expression levels in leaves than in flowers, suggesting their potential involvement in the flower development process and may be linked to the winter and autumn flowering of C. praecox and C. salicifolius.

CONCLUSION

Thirty-three SBPs were identified in C. praecox and C. salicifolius. The evolutionary characteristics and expression patterns were examined in this study. These results provide valuable information to elucidate the evolutionary relationships of the SBP family and help determine the functional characteristics of the SBP genes in subsequent studies.

In-silico identification and characterization of O-methyltransferase gene family in peanut (Arachis hypogaea L.) reveals their putative roles in development and stress tolerance

Cultivated peanut (Arachis hypogaea) is a leading protein and oil-providing crop and food source in many countries. At the same time, it is affected by a number of biotic and abiotic stresses. O-methyltransferases (OMTs) play important roles in secondary metabolism, biotic and abiotic stress tolerance. However, the OMT genes have not been comprehensively analyzed in peanut. In this study, we performed a genome-wide investigation of A. hypogaea OMT genes (AhOMTs). Gene structure, motifs distribution, phylogenetic history, genome collinearity and duplication of AhOMTs were studied in detail. Promoter cis-elements, protein-protein interactions, and micro-RNAs targeting AhOMTs were also predicted. We also comprehensively studied their expression in different tissues and under different stresses. We identified 116 OMT genes in the genome of cultivated peanut. Phylogenetically, AhOMTs were divided into three groups. Tandem and segmental duplication events played a role in the evolution of AhOMTs, and purifying selection pressure drove the duplication process. AhOMT promoters were enriched in several key cis-elements involved in growth and development, hormones, light, and defense-related activities. Micro-RNAs from 12 different families targeted 35 AhOMTs. GO enrichment analysis indicated that AhOMTs are highly enriched in transferase and catalytic activities, cellular metabolic and biosynthesis processes. Transcriptome datasets revealed that AhOMTs possessed varying expression levels in different tissues and under hormones, water, and temperature stress. Expression profiling based on qRT-PCR results also supported the transcriptome results. This study provides the theoretical basis for further work on the biological roles of AhOMT genes for developmental and stress responses.

Genome-Wide Identification of the SQUAMOSA Promoter-Binding Protein-like (SPL) Transcription Factor Family in Sweet Cherry Fruit

Plant-specific SQUAMOSA promoter-binding protein-like (SPL) transcription factors play important regulatory roles during plant growth and development, fruit ripening, inflorescence branching, and biotic and abiotic stresses. However, there have been no identification or systematic studies of the SPL gene family in the sweet cherry. In this study, 12 SPL genes were identified in the sweet cherry reference genome, which were distributed over 6 chromosomes and classified into six groups according to phylogenetic relationships with other SPL gene families. Nine PavSPLs were highly expressed at green fruit stages and dramatically decreased at the onset of fruit ripening, which implied that they were important regulators during fruit development and ripening. The expression patterns of PavSPL genes under ABA, GA, and MeJA treatments showed that the PavSPLs were involved in the process of fruit ripening. A subcellular localization experiment proved that PavSPL4 and PavSPL7 proteins were localized in the nucleus. The genome-wide identification of the SPL gene family provided new insights while establishing an important foundation for sweet cherry studies.

Molecular characterization of SPL gene family during flower morphogenesis and regulation in blueberry

The SPL gene is a plant-specific transcription factor involved in the regulation of plant growth and development, which have been identified in woody plants. The process of floral bud differentiation affects the timing of flowering and fruit set and regulates plant growth, however, the mechanism of regulation of flower development by SPL genes is less studied. In this study, 56 VcSPL genes were identified in the tetraploid blueberry. The VcSPL gene family was classified into six subfamilies, and analysis of cis-elements showed that VcSPL genes were regulated by light, phytohormones (abscisic acid, MeJA), and low temperature. In the evolutionary analysis, segmental replication may play an important role in VcSPL gene amplification. Interestingly, we also studied diploid blueberry (Bilberry), in which 24 SPL genes were identified, and 36 homologous pairs were found, suggesting a high degree of convergence in the syntenic relationship between blueberry (Vaccinium corymbosum L) and bilberry (Vaccinium darrowii). Based on the expression profile, VcSPL genes were expressed at high levels in flowers, shoots, and roots, indicating a diversity of gene functions. Then we selected 20 differentially-expressed SPL genes to further investigate the role of VcSPL in floral induction and initiation. It showed that the genes VcSPL40, VcSPL35, VcSPL45, and VcSPL53 may play a crucial role in the blueberry floral transition phase (from vegetative growth to flower initiation). These results provided important information for understanding and exploring the role of VcSPLs in flower morphogenesis and plant growth.

Transcriptome Analysis of Chinese Cabbage Provides Insights into the Basis of Understanding the Lignin Affected by Low Temperature

Chinese cabbage, which is a cold season crop, can still be damaged at an overly low temperature. It is crucial to study the mechanism of the resistance to low temperature of Chinese cabbage. In this study, the Chinese cabbage 'XBJ' was used as the material, and nine different low temperatures and control samples were treated. Using RNA-seq and lignin content determination, we analyzed 27 samples, and the stained sections of them were observed. A total of 8845 genes were screened for the WGCNA analysis, yielding 17 modules. The GO and KEGG analyses of the modules was highly associated with a low-temperature treatment. The pathways such as 'starch and sucrose metabolism' and 'plant hormone signal transduction' were enriched in modules related to low temperature. Interestingly, L-15DAT-associated MEcoral2 was found to have 14 genes related to the 'lignin biosynthetic process' in the GO annotation. The combination of the determination of the lignin content and the treatment of the stained sections showed that the lignin content of the low-temperatures samples were indeed higher than that of the control. We further explored the expression changes of the lignin synthesis pathway and various genes and found that low temperature affects the expression changes of most genes in the lignin synthesis pathway, leading to the speculation that the lignin changes at low temperature are a defense mechanism against low temperatures. The 29 BrCOMT gene sequence derived from the RNA-seq was non-conserved, and eight BrCOMT genes were differentially expressed. This study provides a new insight into how lignin is affected by low temperature.

Genome-Wide Characterization and Expression Analysis of the SBP-Box Gene Family in Sweet Orange (Citrus sinensis)

SBP-box is an important plant-specific transcription factor family and is involved in diverse biological processes. Here, we identified a total of 15 SBP-BOX genes in the important fruit crop sweet orange (Citrus sinensis) and characterized their gene structures, conserved domain and motif, chromosomal location, and cis-acting regulatory elements. SBP genes were classified into four subfamilies based on the amino acid sequence homology, and the classification is equally strongly supported by the gene and protein structures. Our analysis revealed that segmental duplication events were the main driving force in the evolution of CsSBP genes, and gene pairs might undergo extensive purifying selection. Further synteny analysis of the SBP members among sweet orange and other plant species provides valuable information for clarifying the CsSBP family evolutionary relationship. According to publicly available RNA-seq data and qRT-PCR analysis from various sweet orange tissues, CsSBP genes may be expressed in different tissues and developmental stages. Gene expression analysis showed variable expression profiles of CsSBP genes under various abiotic stresses, such as high and low-temperature, salt, and wound treatments, demonstrating the potential role of SBP members in sweet orange response to abiotic stress. Noticeably, all CsSBP genes were also downregulated in sweet orange upon the infection of an important fungal pathogen Diaporthe citri. Our results provide valuable information for exploring the role of SBP-Box in sweet orange.

The transcriptomic response to heat stress of a jujube (Ziziphus jujuba Mill.) cultivar is featured with changed expression of long noncoding RNAs

Long non-coding RNA (lncRNA) of plant species undergoes dynamic regulation and acts in developmental and stress regulation. Presently, there is little information regarding the identification of lncRNAs in jujube (Ziziphus jujuba Mill.), and it is uncertain whether the lncRNAs could respond to heat stress (HS) or not. In our previous study, a cultivar (Hqing1-HR) of Z. jujuba were treated by HS (45°C) for 0, 1, 3, 5 and 7 days, and it was found that HS globally changed the gene expression by RNA sequencing (RNA-seq) experiments and informatics analyses. In the current study, 8260 lncRNAs were identified successfully from the previous RNA-seq data, and it indicated that lncRNAs expression was also altered globally, suggesting that the lncRNAs might play vital roles in response to HS. Furthermore, bioinformatics analyses of potential target mRNAs of lncRNAs with cis-acting mechanism were performed, and it showed that multiple differentially expressed (DE) mRNAs co-located with DElncRNAs were highly enriched in pathways associated with response to stress and regulation of metabolic process. Taken together, these findings not only provide a comprehensive identification of lncRNAs but also useful clues for molecular mechanism response to HS in jujube.

CaSBP11 Participates in the Defense Response of Pepper to Phytophthora capsici through Regulating the Expression of Defense-Related Genes

Squamosa promoter binding protein (SBP)-box genes are plant-specific transcription factors involved in plant growth and development, morphogenesis and biotic and abiotic stress responses. However, these genes have been understudied in pepper, especially with respect to defense responses to Phytophthora capsici infection. CaSBP11 is a SBP-box family gene in pepper that was identified in our previous research. Silencing CaSBP11 enhanced the defense response of pepper plants to Phytophthora capsici. Without treatment, the expression of defense-related genes (CaBPR1, CaPO1, CaSAR8.2 and CaDEF1) increased in CaSBP11-silenced plants. However, the expression levels of these genes were inhibited under transient CaSBP11 expression. CaSBP11 overexpression in transgenic Nicotiana benthamiana decreased defense responses, while in Arabidopsis, it induced or inhibited the expression of genes in the salicylic acid and jasmonic acid signaling pathways. CaSBP11 overexpression in sid2-2 mutants induced AtNPR1, AtNPR3, AtNPR4, AtPAD4, AtEDS1, AtEDS5, AtMPK4 and AtNDR1 expression, while AtSARD1 and AtTGA6 expression was inhibited. CaSBP11 overexpression in coi1-21 and coi1-22 mutants, respectively, inhibited AtPDF1.2 expression and induced AtPR1 expression. These results indicate CaSBP11 has a negative regulatory effect on defense responses to Phytophthora capsici. Moreover, it may participate in the defense response of pepper to Phytophthora capsici by regulating defense-related genes and the salicylic and jasmonic acid-mediated disease resistance signaling pathways.

Genome-wide identification, characterization, and expression patterns analysis of the SBP-box gene family in wheat (Triticum aestivum L.)

SQUAMOSA promoter-binding protein (SBP)-box genes encode a family of plant-specific transcription factors that play roles in plant growth and development. The characteristics of SBP-box genes in rice (Oryza sativa) and Arabidopsis have been reported, but their potential roles in wheat (Triticum aestivum) are not fully understood. In this study, 48 SBP-box genes (TaSBPs) were identified; they were located in all wheat chromosomes except for 4B and 4D. Six TaSBPs were identified as tandem duplication genes that formed three tandem duplication pairs, while 22 were segmentally duplicated genes that formed 16 segmental duplication pairs. Subcellular localization prediction showed TaSBPs were located in nucleus. Among the 48 TaSBPs, 24 were predicted to be putative targets of TamiR156. Phylogenetic analysis showed that TaSBPs, AtSBPs, and OsSBPs that shared similar functions were clustered into the same subgroups. The phylogenetic relationships between the TaSBPs were supported by the identification of highly conserved motifs and gene structures. Four types of cis-elements––transcription-related, development-related, hormone-related, and abiotic stress-related elements––were found in the TaSBP promoters. Expression profiles indicated most TaSBPs participate in flower development and abiotic stress responses. This study establishes a foundation for further investigation of TaSBP genes and provides novel insights into their biological functions.

Megasporogenesis, microsporogenesis, and female and male gametophyte development in Ziziphus jujuba Mill

Jujube (Ziziphus jujuba Mill.) is an important fruit tree species in China. In this study, we studied the megasporogenesis, microsporogenesis, and female and male gametophyte development of two major jujube cultivars, "Dongzao" and "Mayazao," using the squash technique, improved paraffin section technology, and optical microscopy. Our investigation revealed that both "Dongzao" and "Mayazao" have bilocular ovaries, basal placenta, and anatropous, bitegmic, crassinucellate ovules. The tetrads formed by meiosis of megaspore mother cells are arranged in a straight line or a tetrahedron. Embryo sac development is of the Polygonum type. The flower buds contain five anthers, each having four pollen sacs. The anther wall, which is of the fundamental form, is composed of epidermis, endothecium, one or two middle layers, and glandular tapetum. Mature pollen grains are two-celled and three-colporate. Both "Dongzao" and "Mayazao" can form normal mature pollen grains. Our study, which has revealed the basic phenomena and progression of megasporogenesis, microsporogenesis, and female and male gametophyte development in jujube, has generated important data for further research on jujube cytology and reproductive biology. Finally, our explorations of the cytological mechanism of male sterility in "Dongzao" also have provided a cytological basis for crossbreeding.

Genome-Wide Identification of WRKY Transcription Factors in Chinese jujube (Ziziphus jujuba Mill.) and Their Involvement in Fruit Developing, Ripening, and Abiotic Stress

Chinese jujube (Ziziphus jujuba Mill.) is an economically important fruit crop in China and mainly cultivated on land with high salinity and drought conditions in northern China. WRKY transcription factors (TFs) are involved in plant development and in responses to multiple abiotic stresses. In this study, we identified 61 and 52 putative ZjWRKY TFs in ‘Junzao’ and ‘Dongzao’ at the genome-wide level. Tissue expression profiling showed that 7 genes were constitutively expressed at high level in all tissues of ‘Junzao’. Transcriptome analysis revealed that 39 ZjWRKY genes were expressed during ‘Junzao’ jujube fruit ripening. Among these genes, the transcript abundance of 19 genes were differentially expressed between ‘Junzao’ and ‘Qingjiansuanzao’ fruit. In addition, RT-qPCR analyses revealed that 30, 14, and 18 ZjWRKY genes responded to drought, NaCl, and ABA treatments, respectively. Taken together, ZjWRKY genes expression dynamics during jujube fruit development, ripening, and their differences between jujube and wild jujube would provide insights into their possible roles regulating fruit ripening. In addition, those ZjWRKY genes responded strongly to drought and salt stress, which provide candidate ZjWRKY genes for facilitating tolerance breeding.

Genome-wide analysis of the Catalpa bungei caffeic acid O-methyltransferase (COMT) gene family: identification and expression profiles in normal, tension, and opposite wood

Caffeic acid O-methyltransferase (COMT) is an important protein that participates in lignin synthesis and is associated with the ratio of G-/S-type lignin in plants. COMTs are associated with the wood properties of forest trees; however, little known about the COMT family in Catalpa bungei, a valuable timber tree species in China . We performed a comprehensive analysis of COMT genes in the C. bungei genome by describing the gene structure and phylogenetic relationships of each family member using bioinformatics-based methods. A total of 23 putative COMT genes were identified using the conserved domain sequences and amino acid sequences of COMTs from Arabidopsis thaliana and Populus trichocarpa as probes. Phylogenetic analysis showed that 23 CbuCOMTs can be divided into three groups based on their structural characteristics; five conserved domains were found in the COMT family. Promoter analysis indicated that the CbuCOMT promoters included various cis-acting elements related to growth and development. Real-time quantitative polymerase chain reaction (PCR) analysis showed differential expression among CbuCOMTs. CbuCOMT2, 7, 8, 9, 10, 12, 13, 14, 21, and 23 were mainly expressed in xylem. Only CbuCOMT23 was significantly downregulated in tension wood and upregulated in opposite wood compared to normal wood. Our study provides new information about the CbuCOMT gene family and will facilitate functional characterisation in further research.

Genome-wide identification, characterization, and expression analysis of the expansin gene family in Chinese jujube (Ziziphus jujuba Mill.)

Main conclusion 30 expansin genes were identified in the jujube genome. Phylogenetic analysis classified expansins into 17 subgroups. Closely related expansins share a conserved gene structure. ZjEXPs had different expression patterns in different tissues. Plant-specific expansins were first discovered as pH-dependent cell-wall-loosening proteins involved in diverse physiological processes. No comprehensive analysis of the expansin gene family has yet been carried out at the whole genome level in Chinese jujube (Ziziphus jujuba Mill.). In this study, 30 expansin genes were identified in the jujube genome. These genes, which were distributed with varying densities across 10 of the 12 jujube chromosomes, could be divided into four subfamilies: 19 ZjEXPAs, 3 ZjEXPBs, 1 ZjEXLA, and 7 ZjEXLBs. Phylogenetic analysis of expansin genes in Arabidopsis, rice, apple, grape, and jujube classified these genes into 17 subgroups. Members of the same subfamily and subgroup shared conserved gene structure and motif compositions. Homology analysis identified 20 homologous gene pairs between jujube and Arabidopsis. Further analysis of ZjEXP gene promoter regions uncovered various growth, development and stress-responsive cis-acting elements. Expression analysis and transcript profiling revealed that ZjEXPs had different expression patterns in different tissues at various developmental stages. ZjEXPA4 and ZjEXPA6 were highly expressed in young fruits, ZjEXPA3 and ZjEXPA5 were significantly expressed in flowers, and ZjEXPA7 was specifically expressed in young leaves. The results of this study, the first systematic analysis of the jujube expansin gene family, can serve as a strong foundation for further elucidation of the physiological functions and biological roles of jujube expansin genes.

Genome-wide characterization and expression analyses of the MYB superfamily genes during developmental stages in Chinese jujube

The MYB transcription factor (TF) superfamily, one of the largest gene superfamilies, regulates a variety of physiological processes in plants. Although many MYB superfamily genes have been identified in plants, the MYB TFs in Chinese jujube (Ziziphus jujuba Mill.) have not been fully identified and characterized. Additionally, the functions of these genes remain unclear. In total, we identified 171 MYB superfamily genes in jujube and divided them into five subfamilies containing 99 genes of the R2R3-MYB subfamily, 58 genes of the MYB-related subfamily, four genes of the R1R2R3-MYB subfamily, one gene of the 4R-MYB subfamily, and nine genes of the atypical MYB subfamily. The 99 R2R3-MYB genes of jujube were divided into 35 groups, C1–C35, and the 58 MYB-related genes were divided into the following groups: the R-R-type, CCA1-like, I-box-binding-like, TBP-like, CPC-like, and Chinese jujube-specific groups. ZjMYB genes in jujube were well supported by additional highly conserved motifs and exon/intron structures. Most R1 repeats of MYB-related proteins comprised the R2 repeat and had highly conserved EED and EEE residue groups in jujube. Three tandem duplicated gene pairs were found on 12 chromosomes in jujube. According to an expression analysis of 126 ZjMYB genes, MYB-related genes played important roles in jujube development and fruit-related biological processes. The total flavonoid content of jujube fruit decreased as ripening progressed. A total of 93 expressed genes were identified in the RNA-sequencing data from jujube fruit, and 56 ZjMYB members presented significant correlations with total flavonoid contents by correlation analysis. Five pairs of paralogous MYB genes within jujube were composed of nine jujube MYB genes. A total of 14 ZjMYB genes had the same homology to the MYB genes of Arabidopsis and peach, indicating that these 14 MYB genes and their orthologs probably existed before the ancestral divergence of the MYB superfamily. We used a synteny analysis of MYB genes between jujube and Arabidopsis to predict that the functions of the ZjMYBs involve flavonoid/phenylpropanoid metabolism, the light signaling pathway, auxin signal transduction, and responses to various abiotic stresses (cold, drought, and salt stresses). Additionally, we speculate that ZjMYB108 is an important TF involved in the flavonoid metabolic pathway. This comprehensive analysis of MYB superfamily genes in jujube lay a solid foundation for future comprehensive analyses of ZjMYB gene functions.

Identification and Expression Analyses of SBP-Box Genes Reveal Their Involvement in Abiotic Stress and Hormone Response in Tea Plant (Camellia sinensis)

The SQUAMOSA promoter binding protein (SBP)-box gene family is a plant-specific transcription factor family. This family plays a crucial role in plant growth and development. In this study, 20 SBP-box genes were identified in the tea plant genome and classified into six groups. The genes in each group shared similar exon-intron structures and motif positions. Expression pattern analyses in five different tissues demonstrated that expression in the buds and leaves was higher than that in other tissues. The cis-elements and expression patterns of the CsSBP genes suggested that the CsSBP genes play active roles in abiotic stress responses; these responses may depend on the abscisic acid (ABA), gibberellic acid (GA), and methyl jasmonate (MeJA) signaling pathways. Our work provides a comprehensive understanding of the CsSBP family and will aid in genetically improving tea plants.

Comparative genome analysis of jujube witches'-broom Phytoplasma, an obligate pathogen that causes jujube witches'-broom disease

BACKGROUND

JWB phytoplasma is a kind of insect-transmitted and uncultivable bacterial plant pathogen causeing a destructive Jujube disease. To date, no genome information about JWB phytoplasma has been published, which hindered its characterization at genomic level. To understand its pathogenicity and ecology, the genome of a JWB phytoplasma isolate jwb-nky was sequenced and compared with other phytoplasmas enabled us to explore the mechanisms of genomic rearrangement.

RESULTS

The complete genome sequence of JWB phytoplasma (jwb-nky) was determined, which consisting of one circular chromosome of 750,803 bp with a GC content of 23.3%. 694 protein-encoding genes, 2 operons for rRNA genes and 31 tRNA genes as well as 4 potential mobile units (PMUs) containing clusters of DNA repeats were identified. Based on PHIbaes analysis, a large number of genes were genome-specific and approximately 13% of JWB phytoplasma genes were predicted to be associated with virulence. Although transporters for maltose, dipeptides/oligopeptides, spermidine/putrescine, cobalt, Mn/Zn and methionine were identified, KEGG pathway analysis revealed the reduced metabolic capabilities of JWB phytoplasma. Comparative genome analyses between JWB phytoplasma and other phytoplasmas shows the occurrence of large-scale gene rearrangements. The low synteny with other phytoplasmas indicated that the expansion of multiple gene families/duplication probably occurred separately after differentiation.

CONCLUSIONS

In this study, the complete genome sequence of a JWB phytoplasma isolate jwb-nky that causing JWB disease was reported for the first time and a number of species-specific genes were identified in the genome. The study enhanced our understandings about genomic basis and the pathogenicity mechanism of this pathogen, which will aid in the development of improved strategies for efficient management of JWB diseases.

Genome-Wide Screening and Characterization of the Dof Gene Family in Physic Nut (Jatropha curcas L.)

Physic nut (Jatropha curcas L.) is a species of flowering plant with great potential for biofuel production and as an emerging model organism for functional genomic analysis, particularly in the Euphorbiaceae family. DNA binding with one finger (Dof) transcription factors play critical roles in numerous biological processes in plants. Nevertheless, the knowledge about members, and the evolutionary and functional characteristics of the Dof gene family in physic nut is insufficient. Therefore, we performed a genome-wide screening and characterization of the Dof gene family within the physic nut draft genome. In total, 24 JcDof genes (encoding 33 JcDof proteins) were identified. All the JcDof genes were divided into three major groups based on phylogenetic inference, which was further validated by the subsequent gene structure and motif analysis. Genome comparison revealed that segmental duplication may have played crucial roles in the expansion of the JcDof gene family, and gene expansion was mainly subjected to positive selection. The expression profile demonstrated the broad involvement of JcDof genes in response to various abiotic stresses, hormonal treatments and functional divergence. This study provides valuable information for better understanding the evolution of JcDof genes, and lays a foundation for future functional exploration of JcDof genes.