Overexpression of AtDOF4.7, an Arabidopsis DOF family transcription factor, induces floral organ abscission deficiency in Arabidopsis

Abscission in plants: from mechanism to applications

Abscission refers to the natural separation of plant structures from their parent plants, regulated by external environmental signals or internal factors such as stress and aging. It is an advantageous process as it enables plants to shed unwanted organs, thereby regulating nutrient allocation and ensuring the dispersal of fruits and seeds from the parent. However, in agriculture and horticulture, abscission can severely reduce crop quality and yield. In this review, we summarize the recent advances in plant abscission from the perspectives of developmental and molecular biology, emphasizing the diverse regulatory networks across different plant lineages, from model plants to crops. The sophisticated process of plant abscission involves several overlapping steps, including the differentiation of the abscission zone, activation of abscission, tissue detachment, and formation of a protective layer. Finally, we discuss the potential applications of physiological modifications and genetic manipulations of plant abscission in sustainable agriculture in the future.

Genome assembly of autotetraploid Actinidia arguta highlights adaptive evolution and enables dissection of important economic traits

Actinidia arguta, the most widely distributed Actinidia species and the second cultivated species in the genus, can be distinguished from the currently cultivated Actinidia chinensis on the basis of its small and smooth fruit, rapid softening, and excellent cold tolerance. Adaptive evolution of tetraploid Actinidia species and the genetic basis of their important agronomic traits are still unclear. Here, we generated a chromosome-scale genome assembly of an autotetraploid male A. arguta accession. The genome assembly was 2.77 Gb in length with a contig N50 of 9.97 Mb and was anchored onto 116 pseudo-chromosomes. Resequencing and clustering of 101 geographically representative accessions showed that they could be divided into two geographic groups, Southern and Northern, which first diverged 12.9 million years ago. A. arguta underwent two prominent expansions and one demographic bottleneck from the mid-Pleistocene climate transition to the late Pleistocene. Population genomics studies using paleoclimate data enabled us to discern the evolution of the species' adaptation to different historical environments. Three genes (AaCEL1, AaPME1, and AaDOF1) related to flesh softening were identified by multi-omics analysis, and their ability to accelerate flesh softening was verified through transient expression assays. A set of genes that characteristically regulate sexual dimorphism located on the sex chromosome (Chr3) or autosomal chromosomes showed biased expression during stamen or carpel development. This chromosome-level assembly of the autotetraploid A. arguta genome and the genes related to important agronomic traits will facilitate future functional genomics research and improvement of A. arguta.

Identification of PavHB16 gene in Prunus avium and validation of its function in Arabidopsis thaliana

Sweet cherry (Prunus avium L.) is one of the most economically important fruits in the world. However, severe fruit abscission has brought significant challenges to the cherry industry. To better understand the molecular regulation mechanisms underlying excessive fruit abscission in sweet cherry, the fruit abscission characteristics, the anatomical characteristics of the abscission zone (AZ), as well as a homeodomain-Leucine Zipper gene family member PavHB16 function were analyzed. The results showed that the sweet cherry exhibited two fruit abscission peak stages, with the "Brooks" cultivar demonstrating the highest fruit-dropping rate (97.14%). During these two fruit abscission peak stages, both the retention pedicel and the abscising pedicel formed AZs. but the AZ in the abscising pedicel was more pronounced. In addition, a transcription factor, PavHB16, was identified from sweet cherry. The evolutionary analysis showed that there was high homology between PavHB16 and AtHB12 in Arabidopsis. Moreover, the PavHB16 protein was localized in the nucleus. Overexpression of PavHB16 in Arabidopsis accelerated petal shedding. In the PavHB16-overexpressed lines, the AZ cells in the pedicel became smaller and denser, and the expression of genes involved in cell wall remodeling, such as cellulase 3 gene (AtCEL3), polygalacturonase 1 (AtPG1), and expandin 24(AtEXPA24) were upregulated. The results suggest that PavHB16 may promote the expression of genes related to cell wall remodeling, ultimately facilitating fruit abscission. In summary, this study cloned the sweet cherry PavHB16 gene and confirmed its function in regulating sweet cherry fruit abscission, which provided new data for further study on the fruit abscission mechanism.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01443-8.

The zinc finger protein 3 of Arabidopsis thaliana regulates vegetative growth and root hair development

Introduction

Zinc finger protein 3 (ZFP3) and closely related C2H2 zinc finger proteins have been identified as regulators of abscisic acid signals and photomorphogenic responses during germination. Whether ZFP3 and related ZFP factors regulate plant development is, however, not known.

Results

ZFP3 overexpression reduced plant growth, limited cell expansion in leaves, and compromised root hair development. The T-DNA insertion zfp3 mutant and transgenic lines with silenced ZFP1, ZFP3, ZFP4, and ZFP7 genes were similar to wild-type plants or had only minor differences in plant growth and morphology, probably due to functional redundancy. RNAseq transcript profiling identified ZFP3-controlled gene sets, including targets of ABA signaling with reduced transcript abundance. The largest gene set that was downregulated by ZFP3 encoded regulatory and structural proteins in cell wall biogenesis, cell differentiation, and root hair formation. Chromatin immunoprecipitation confirmed ZFP3 binding to several target promoters.

Discussion

Our results suggest that ZFP3 and related ZnF proteins can modulate cellular differentiation and plant vegetative development by regulating the expression of genes implicated in cell wall biogenesis.

Phytohormones and candidate genes synergistically regulate fruitlet abscission in Areca catechu L

BACKGROUND

The fruit population of most plants is under the control of a process named "physiological drop" to selectively abort some developing fruitlets. However, frequent fruitlet abscission severely restricts the yield of Areca catechu. To reveal the physiological and molecular variations in this process, we detected the variation of phytohormone levels in abscised and non-abscised fruitlets in A. catechu.

RESULTS

The levels of gibberellin acid, jasmonic acid, salicylic acid, abscisic acid and zeatin were elevated, while the indole-3-acetic acid and indole-3-carboxaldehyde levels were declined in the "about-to-abscise" part (AB) of abscission zone (AZ) compared to the "non-abscised" part (CK). Then the differentially expressed genes (DEGs) between AB and CK were screened based on transcriptome data. DEGs involved in phytohormone synthesis, response and transportation were identified as key genes. Genes related to cell wall biosynthesis, degradation, loosening and modification, and critical processes during fruit abscission were identified as role players. In addition, genes encoding transcription factors, such as NAC, ERF, WRKY, MADS and Zinc Finger proteins, showed differentially expressed patterns between AB and CK, were also identified as candidates.

CONCLUSIONS

These results unraveled a phytohormone signaling cross talk and key genes involved in the fruitlet abscission process in A. catechu. This study not only provides a theoretical basis for fruitlet abscission in A. catechu, but also identified many candidate genes or potential molecular markers for further breeding of fruit trees.

GhDof1.7, a Dof Transcription Factor, Plays Positive Regulatory Role under Salinity Stress in Upland Cotton

Salt stress is a major abiotic stressor that can severely limit plant growth, distribution, and crop yield. DNA-binding with one finger (Dof) is a plant-specific transcription factor that plays a crucial role in plant growth, development, and stress response. In this study, the function of a Dof transcription factor, GhDof1.7, was investigated in upland cotton. The GhDof1.7 gene has a coding sequence length of 759 base pairs, encoding 252 amino acids, and is mainly expressed in roots, stems, leaves, and inflorescences. Salt and abscisic acid (ABA) treatments significantly induced the expression of GhDof1.7. The presence of GhDof1.7 in Arabidopsis may have resulted in potential improvements in salt tolerance, as suggested by a decrease in H2O2 content and an increase in catalase (CAT) and superoxide dismutase (SOD) activities. The GhDof1.7 protein was found to interact with GhCAR4 (C2-domain ABA-related 4), and the silencing of either GhDof1.7 or GhCAR4 resulted in reduced salt tolerance in cotton plants. These findings demonstrate that GhDof1.7 plays a crucial role in improving the salt tolerance of upland cotton and provide insight into the regulation of abiotic stress response by Dof transcription factors.

Brt9SIDA/IDALs as peptide signals mediate diverse biological pathways in plants

As signal molecules, plant peptides play key roles in intercellular communication during growth and development, as well as stress responses. The 14-amino-acid (aa) INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) peptide was originally identified to play an essential role in the floral organ abscission of Arabidopsis. It is synthesized from its precursor, a small protein containing 77-aa residues with an N-terminal signal peptide sequence. Recently, the IDA/IDA-like (IDLs) genes are isolated in several angiosperms and are highly conserved in land plants. In addition, IDA/IDLs are not only involved in organ abscission but also function in multiple biological processes, including biotic and abiotic stress responses. Here, we summarize the post-translational modification and proteolytic processing, the evolutionary conservation, and the potential regulatory function of IDA/IDLs, and also present future perspectives to investigate the IDA/IDLs signaling pathway. We anticipate that this detailed knowledge will help to improve the understanding of the molecular mechanism of plant peptide signaling.

A LcDOF5.6-LcRbohD regulatory module controls the reactive oxygen species-mediated fruitlet abscission in litchi

Reactive oxygen species (ROS) have been emerging as a key regulator in plant organ abscission. However, the mechanism underlying the regulation of ROS homeostasis in the abscission zone (AZ) is not completely established. Here, we report that a DOF (DNA binding with one finger) transcription factor LcDOF5.6 can suppress the litchi fruitlet abscission through repressing the ROS accumulation in fruitlet AZ (FAZ). The expression of LcRbohD, a homolog of the Arabidopsis RBOHs that are critical for ROS production, was significantly increased during the litchi fruitlet abscission, in parallel with an increased accumulation of ROS in FAZ. In contrast, silencing of LcRbohD reduced the ROS accumulation in FAZ and decreased the fruitlet abscission in litchi. Using in vitro and in vivo assays, we revealed that LcDOF5.6 was shown to inhibit the expression of LcRbohD via direct binding to its promoter. Consistently, silencing of LcDOF5.6 increased the expression of LcRbohD, concurrently with higher ROS accumulation in FAZ and increased fruitlet abscission. Furthermore, the expression of key genes (LcIDL1, LcHSL2, LcACO2, LcACS1, and LcEIL3) in INFLORESCENCE DEFICIENT IN ABSCISSION signaling and ethylene pathways were altered in LcRbohD-silenced and LcDOF5.6-silenced FAZ cells. Taken together, our results demonstrate an important role of the LcDOF5.6-LcRbohD module during litchi fruitlet abscission. Our findings provide new insights into the molecular regulatory network of organ abscission.

GmDof41 regulated by the DREB1-type protein improves drought and salt tolerance by regulating the DREB2-type protein in soybean

Despite their essential and multiple roles in biological processes, the molecular mechanism of Dof transcription factors (TFs) for responding to abiotic stresses is rarely reported in plants. We identified a soybean Dof gene GmDof41 which was involved in the responses to drought, salt, and exogenous ABA stresses. Overexpression of GmDof41 in soybean transgenic hairy roots attenuated H2O2 accumulation and regulated proline homeostasis, resulting in the drought and salt tolerance. Yeast one-hybrid and electrophoretic mobility shift assay (EMSA) illustrated that GmDof41 was regulated by the DREB1-type protein GmDREB1B;1 that could improve drought and salt tolerance in plants. Further studies illustrated GmDof41 can directly bind to the promoter of GmDREB2A which encodes a DREB2-type protein and affects abiotic stress tolerance in plants. Collectively, our results suggested that GmDof41 positively regulated drought and salt tolerance by correlating with GmDREB1B;1 and GmDREB2A. This study provides an important basis for further exploring the abiotic stress-tolerance mechanism of Dof TFs in soybean.

DOF transcription factors: Specific regulators of plant biological processes

Plant biological processes, such as growth and metabolism, hormone signal transduction, and stress responses, are affected by gene transcriptional regulation. As gene expression regulators, transcription factors activate or inhibit target gene transcription by directly binding to downstream promoter elements. DOF (DNA binding with One Finger) is a classic transcription factor family exclusive to plants that is characterized by its single zinc finger structure. With breakthroughs in taxonomic studies of different species in recent years, many DOF members have been reported to play vital roles throughout the plant life cycle. They are not only involved in regulating hormone signals and various biotic or abiotic stress responses but are also reported to regulate many plant biological processes, such as dormancy, tissue differentiation, carbon and nitrogen assimilation, and carbohydrate metabolism. Nevertheless, some outstanding issues remain. This article mainly reviews the origin and evolution, protein structure, and functions of DOF members reported in studies published in many fields to clarify the direction for future research on DOF transcription factors.

Exploration of the genomic atlas of Dof transcription factor family across genus Oryza provides novel insights on rice breeding in changing climate

DNA-binding with one finger (Dof) transcription factors have been demonstrated to regulate various stresses and developmental processes in plants. Their identification and comparative evolutionary analyses in cultivated and wild species of genus oryza were yet to be explored. In this context, we report a comprehensive genomics atlas of DNA-binding with one finger (Dof) family genes in 13 diverse rice genomes (five cultivated and eight rice wild-relatives) through a genome-wide scanning approach. A galore of 238 Dof genes, identified across the genus Oryza, are categorized into seven distinct subgroups by comparative phylogenetic analysis with the model plant Arabidopsis. Conserved motifs and gene structure analyses unveiled the prevalence of species- and subgroups-specific structural and functional diversity that is expediating with the evolutionary period. Our results indicate that Dof genes might have undergone strong purifying selections and segmental duplications to expand their gene family members in corresponding Oryza genomes. We speculate that miR2927 potentially targets the Dof domain to regulate gene expression under different climatic conditions, which are supported by in-silico and wet-lab experiments-based expression profiles. In a nutshell, we report several superior haplotypes significantly associated with early flowering in a treasure trove of 3,010 sequenced rice accessions and have validated these haplotypes with two years of field evaluation-based flowering data of a representative subpanel. Finally, we have provided some insights on the resolution of Oryza species phylogeny discordance and divergence highlighting the mosaic evolutionary history of the genus Oryza. Overall, this study reports a complete genomic landscape of the Dof family in cultivated and wild Oryza species that could greatly facilitate in fast-track development of early maturing and climate-resilient rice cultivars through modern haplotype-led breeding.

Genome-Wide Identification of the DOF Gene Family Involved in Fruitlet Abscission in Areca catechu L

Fruitlet abscission frequently occurs in Areca catechu L. and causes considerable production loss. However, the inducement mechanism of fruitlet abscission remains mysterious. In this study, we observed that the cell architecture in the abscission zone (AZ) was distinct with surrounding tissues, and varied obviously before and after abscission. Transcriptome analysis of the “about-to-abscise” and “non-abscised” AZs were performed in A. catechu, and the genes encoding the plant-specific DOF (DNA-binding with one finger) transcription factors showed a uniform up-regulation in AZ, suggesting a role of the DOF transcription in A. catechu fruitlet abscission. In total, 36 members of the DOF gene family distributed in 13 chromosomes were identified from the A. catechu genome. The 36 AcDOF genes were classified into nine subgroups based on phylogenic analysis. Six of them showed an AZ-specific expression pattern, and their expression levels varied according to the abscission process. In total, nine types of phytohormone response cis-elements and five types of abiotic stress related cis-elements were identified in the promoter regions of the AcDOF genes. In addition, histochemical staining showed that lignin accumulation of vascular bundles in AZ was significantly lower than that in pedicel and mesocarp, indicating the specific characteristics of the cell architecture in AZ. Our data suggests that the DOF transcription factors might play a role in fruitlet abscission regulation in A. catechu.

Genome-wide identification, phylogenetic and expression pattern analysis of Dof transcription factors in blueberry (Vaccinium corymbosum L.)

Background

DNA binding with one finger (Dof) proteins are plant-specific transcription factor (TF) that plays a significant role in various biological processes such as plant growth and development, hormone regulation, and resistance to abiotic stress. The Dof genes have been identified and reported in multiple plants, but so far, the whole genome identification and analysis of Dof transcription factors in blueberry (Vaccinium corymbosum L.) have not been reported yet.

Methods

Using the Vaccinium genome, we have identified 51 VcDof genes in blueberry. We have further analyzed their physicochemical properties, phylogenetic relationships, gene structure, collinear analysis, selective evolutionary pressure, cis-acting promoter elements, and tissue and abiotic stress expression patterns.

Results

Fifty-one VcDof genes were divided into eight subfamilies, and the genes in each subfamily contained similar gene structure and motif ordering. A total of 24 pairs of colinear genes were screened; VcDof genes expanded mainly due to whole-genome duplication, which was subjected to strong purifying selection pressure during the evolution. The promoter of VcDof genes contains three types of cis-acting elements for plant growth and development, phytohormone and stress defense responsiveness. Expression profiles of VcDof genes in different tissues and fruit developmental stages of blueberry indicated that VcDof2 and VcDof45 might play a specific role in anthesis and fruit growth and development. Expression profiles of VcDof genes in different stress indicated that VcDof1, VcDof11, and VcDof15 were highly sensitive to abiotic stress. This study provides a theoretical basis for further clarifying the biological function of Dof genes in blueberry.

Selection and functional identification of Dof genes expressed in response to nitrogen in Populus simonii × Populus nigra

In plants, Dof transcription factors are involved in regulating the expression of a series of genes related to N uptake and utilization. Therefore, the present study investigated how DNA-binding with one finger (Dof) genes are expressed in response to nitrogen (N) form and concentration to clarify the role of Dof genes and their functions in promoting N assimilation and utilization in poplar. The basic characteristics and expression patterns of Dof genes in poplar were analyzed by the use of bioinformatics methods. Dof genes expressed in response to N were screened, after which the related genes were cloned and transformed into Arabidopsis thaliana; the physiological indexes and the expression of related genes were subsequently determined. The function of Dof genes was then verified in Arabidopsis thaliana plants grown in the presence of different N forms and concentrations. Forty-four Dof genes were identified, most of which were expressed in the roots and young leaves, and some of the Dof genes were expressed under ammonia- and nitrate-N treatments. Three genes related to N induction were cloned, their proteins were found to localize in the nucleus, and PnDof30 was successfully transformed into Arabidopsis thaliana for functional verification. On comparing Arabidopsis thaliana with WT Arabidopsis thaliana plants, Arabidopsis thaliana plants overexpressing the Dof gene grew better under low N levels; the contents of soluble proteins and chlorophyll significantly increased, while the soluble sugar content significantly decreased. The expressions of several AMT, NRT, and GS genes were upregulated, while the expressions of several others were downregulated, and the expression of PEPC and PK genes significantly increased. In addition, the activity of PEPC, PK, GS, and NR enzymes significantly increased. The results showed that overexpression of PnDof30 significantly increased the level of carbon and N metabolism and improved the growth of transgenic Arabidopsis thaliana plants under low-N conditions. The study revealed the biological significance of poplar Dof transcription factors in N response and regulation of related downstream gene expression and provided some meaningful clues to explain the huge difference between poplar and Arabidopsis thaliana transformed by exogenous Dof gene, which could promote the comprehensive understanding of the molecular mechanism of efficient N uptake and utilization in trees.

The association of HpDof1.7 and HpDof5.4 with soluble sugar accumulation in pitaya fruit by transcriptionally activating sugar metabolic genes

Soluble sugar is one of the important factors affecting fruit flavor and quality. Here, we report the identification of two Dof (DNA-binding with one finger) transcription factors termed HpDof1.7 and HpDof5.4, and their roles in influencing sugar accumulation in pitayas. HpDof1.7 and HpDof5.4 shared a similar expression pattern with sugar metabolism-related genes HpSuSy1 and HpINV2, and sugar transporter genes HpTMT2 and HpSWEET14 during pitayas maturation, and their expression pattern was also consistent with the accumulation of glucose and fructose, which were the predominant sugars in pitayas. HpDof1.7 and HpDof5.4 were both typical nucleus-localized proteins with trans-activation ability. Gel mobility shift assay revealed that HpDof1.7 and HpDof5.4 were bound to promoters of HpSuSy1, HpINV2, HpTMT2 and HpSWEET14. Finally, transient expression assays in tobacco leaves showed that HpDof1.7 and HpDof5.4 increased the activities of HpSuSy1, HpINV2, HpTMT2 and HpSWEET14 promoters, thus facilitating sugar accumulation by transcriptionally enhancing sugar metabolic pathway genes. Our findings provide a new perspective on the regulatory mechanisms of Dof transcription factors in sugar accumulation and pitaya fruit quality formation.

Two Dof transcription factors promote flavonoid synthesis in kumquat fruit by activating C-glucosyltransferase

Although DNA binding with one finger (Dof) constitutes a crucial plant-specific family of transcription factors (TFs) that plays important roles in a wide range of biological processes, the molecular mechanisms underlying Dof regulation of flavonoid biosynthesis in plants remain largely unknown. Here, we characterized 28 Dof genes (FhDof1-FhDof28) from the 'Hongkong' kumquat (Fortunella hindsii) cultivar genome. Promoter analysis and transcriptome profiling revealed that four FhDofs - FhDof4, FhDof9, FhDof15, and FhDof16 - may be involved in flavonoid biosynthesis through binding to the flavonoid C-glycosyltransferase (FhCGT) promoter. We cloned homologous genes of four FhDofs, designated as FcDof4, FcDof9, FcDof15, FcDof16, and a homologous gene of FhCGT, designated as FcCGT, from the widely cultivated 'HuaPi' kumquat (F. crassifolia). Quantitative reverse transcription-polymerase chain reaction analysis revealed that FcDof4 and FcDof16 were significantly correlated with FcCGT expression during development stages in the 'HuaPi' fruit (Pearson's correlation coefficient > 0.7) and were localized to the nucleus. Results of yeast one-hybrid, electrophoretic mobility shift, and dual-luciferase assays indicated that the two FcDofs trigger FcCGT expression by specifically binding to its promoters. Moreover, transient overexpression of FcDof4 and FcDof16 enhances the transcription of structural genes in the flavonoid biosynthetic pathway and increases C-glycosylflavonoid content. Our results provide strong evidence that the TFs FcDof4 and FcDof16 promote flavonoid synthesis in kumquat fruit by activating FcCGT expression.

Genome-wide analysis of Dof transcription factors and their response to cold stress in rice (Oryza sativa L.)

Background

Rice (Oryza sativa L.) is a food crop for humans worldwide. However, temperature has an effect during the vegetative and reproductive stages. In high-latitude regions where rice is cultivated, cold stress is a major cause of yield loss and plant death. Research has identified a group of plant-specific transcription factors, DNA binding with one zinc fingers (DOFs), with a diverse range of functions, including stress signaling and stress response during plant growth. The aim of this study was to identify Dof genes in two rice subspecies, indica and japonica, and screen for Dof genes that may be involved in cold tolerance during plant growth.

Results

A total of 30 rice Dofs (OsDofs) were identified using bioinformatics and genome-wide analyses and phylogenetically analyzed. The 30 OsDOFs were classified into six subfamilies, and 24 motifs were identified based on protein sequence alignment. The chromosome locations of OsDofs were determined and nine gene duplication events were identified. A joint phylogenetic analysis was performed on DOF protein sequences obtained from four monocotyledon species to examine the evolutionary relationship of DOF proteins. Expression profiling of OsDofs from two japonica cultivars (Longdao5, which is cold-tolerant, and Longjing11, which is cold-sensitive) revealed that OsDof1 and OsDof19 are cold-inducible genes. We examined the seed setting rates in OsDof1- and OsDof19-overexpression and RNAi lines and found that OsDof1 showed a response to cold stress.

Conclusions

Our investigation identified OsDof1 as a potential target for genetic breeding of rice with enhanced cold tolerance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08104-0.

Identification of Novel Mutations in Arabidopsis thaliana DOF 4.2 Coding Gene

Purpose: DOF (DNA-binding with One Finger) proteins are plant-specific transcription factors which mediate numerous biological processes. The purpose of the current study is to report new naturally occurring mutations in the gene encoding for one of the members of DOF proteins named DOF 4.2.

Methods: The expression of zinc finger domain of DOF 4.2 (DOF 4.2-ZF) was investigated by first synthesis of cDNA library using different parts of Arabidopsis thaliana plant. Then the coding sequence for zinc finger domain of DOF 4.2 protein was prepared using nested PCR experiment and cloned into pGEX-6P-1 expression vector. Finally, the prepared construct was used for protein expression. Furthermore, molecular dynamics (MD) simulation was carried out to predict DNA binding affinity of DOF 4.2-ZF using AMBER package.

Results: For the first time a new variant of DOF 4.2-ZF protein with three mutations was detected. One of the mutations is silent while the other two mutations lead to amino acid replacement (S18G) as well as introduction of a stop codon ultimately resulting in a truncated protein production. In order to investigate whether the truncated form is able to recognize DNA binding motif, MD simulations were carried out and the results showed that the chance of binding of DOF 4.2-ZF protein to cognate DNA in its truncated form is very low.

Conclusion: The findings demonstrated that the observed mutations adversely affect the DNA binding ability of the truncated form of DOF4.2 if it is expressed in the mutant variant of A. thaliana used in this study.

Genome-wide binding analysis of the tomato transcription factor SlDof1 reveals its regulatory impacts on fruit ripening

The DNA binding with one finger (Dof) proteins are plant-specific transcription factors involved in a variety of biological processes. However, little is known about their functions in fruit ripening, a flowering-plant-specific process that is required for seed maturation and dispersal. Here, we found that the tomato Dof transcription factor SlDof1, is necessary for normal fruit ripening. Knockdown of SlDof1 expression by RNA interference delayed ripening-related processes, including lycopene synthesis and ethylene production. Transcriptome profiling indicated that SlDof1 influences the expression of hundreds of genes, and a chromatin immunoprecipitation sequencing revealed a large number of SlDof1 binding sites. A total of 312 genes were identified as direct targets of SlDof1, among which 162 were negatively regulated by SlDof1 and 150 were positively regulated. The SlDof1 target genes were involved in a variety of metabolic pathways, and follow-up analyses verified that SlDof1 directly regulates some well-known ripening-related genes including ACS2 and PG2A as well as transcriptional repressor genes such as SlIAA27. Our findings provide insights into the transcriptional regulatory networks underlying fruit ripening and highlight a gene potentially useful for genetic engineering to control ripening.

Genomic editing of intronic enhancers unveils their role in fine-tuning tissue-specific gene expression in Arabidopsis thaliana

Enhancers located in introns are abundant and play a major role in the regulation of gene expression in mammalian species. By contrast, the functions of intronic enhancers in plants have largely been unexplored and only a handful of plant intronic enhancers have been reported. We performed a genome-wide prediction of intronic enhancers in Arabidopsis thaliana using open chromatin signatures based on DNase I sequencing. We identified 941 candidate intronic enhancers associated with 806 genes in seedling tissue and 1,271 intronic enhancers associated with 1,069 genes in floral tissue. We validated the function of 15 of 21 (71%) of the predicted intronic enhancers in transgenic assays using a reporter gene. We also created deletion lines of three intronic enhancers associated with two different genes using CRISPR/Cas. Deletion of these enhancers, which span key transcription factor binding sites, did not abolish gene expression but caused varying levels of transcriptional repression of their cognate genes. Remarkably, the transcriptional repression of the deletion lines occurred at specific developmental stages and resulted in distinct phenotypic effects on plant morphology and development. Clearly, these three intronic enhancers are important in fine-tuning tissue- and development-specific expression of their cognate genes.

Cross-talk between transcriptome, phytohormone and HD-ZIP gene family analysis illuminates the molecular mechanism underlying fruitlet abscission in sweet cherry (Prunus avium L)

BACKGROUND

The shedding of premature sweet cherry (Prunus avium L) fruitlet has significantly impacted production, which in turn has a consequential effect on economic benefits.

RESULT

To better understand the molecular mechanism of sweet cherry fruitlet abscission, pollen viability and structure had been observed from the pollination trees. Subsequently, the morphological characters of the shedding fruitlet, the plant hormone titers of dropping carpopodium, the transcriptome of the abscising carpopodium, as well as the HD-ZIP gene family were investigated. These findings showed that the pollens giving rise to heavy fruitlet abscission were malformed in structure, and their viability was lower than the average level. The abscising fruitlet and carpopodium were characterized in red color, and embryos of abscising fruitlet were aborted, which was highly ascribed to the low pollen viability and malformation. Transcriptome analysis showed 6462 were significantly differentially expressed, of which 2456 genes were up-regulated and 4006 down-regulated in the abscising carpopodium. Among these genes, the auxin biosynthesis and signal transduction genes (α-Trp, AUX1), were down-regulated, while the 1-aminocyclopropane-1-carboxylate oxidase gene (ACO) affected in ethylene biosynthesis, was up-regulated in abscising carpopodium. About genes related to cell wall remodeling (CEL, PAL, PG EXP, XTH), were up-regulated in carpopodium abscission, which reflecting the key roles in regulating the abscission process. The results of transcriptome analysis considerably conformed with those of proteome analysis as documented previously. In comparison with those of the retention fruitlet, the auxin contents in abscising carpopodium were significantly low, which presumably increased the ethylene sensitivity of the abscission zone, conversely, the abscisic acid (ABA) accumulation was considerably higher in abscising carpopodium. Furthermore, the ratio of (TZ + IAA + GA3) / ABA also obviously lower in abscising carpopodium. Besides, the HD-ZIP gene family analysis showed that PavHB16 and PavHB18 were up-regulated in abscising organs.

CONCLUSION

Our findings combine morphology, cytology and transcriptional regulation to reveal the molecular mechanism of sweet cherry fruitlet abscission. It provides a new perspective for further study of plant organ shedding.

Transcription factor CsDOF regulates glutamine metabolism in tea plants (Camellia sinensis)

Glutamine plays a critical role in ammonium assimilation, and contributes substantially to the taste and nutritional quality of tea. To date, little research has been done on glutamine synthesis in tea plants. Here, a zinc finger protein CsDOF and a glutamine synthetase (GS)-encoding gene CsGS2 from tea plant (Camellia sinensis cv 'Shuchazao') were characterized, and their role in glutamine biosynthesis was determined using transient suppression assays in tea leaves and overexpression in Arabidopsis thaliana. The expression patterns of CsDOF and CsGS2, the GS activity and the glutamine content of photosynthetic tissues (leaf and bud) were significantly induced by shade. Suppressing the expression of CsDOF resulted in downregulated expression of CsGS2 and reduction of the leaf glutamine content. Moreover, in CsDOF-silenced plants, the expression of CsDOF and the glutamine content under shade treatment were higher than in natural light. The glutamine content and CsGS2 transcript level were also decreased in tea leaves when CsGS2 was suppressed, while they were higher under shade treatment than in natural light in CsGS2-silenced plants. In addition, the glutamine content and GS2 transcript level were increased when CsDOF and CsGS2 was overexpressed in Arabidopsis thaliana, respectively. In binding analyses, CsDOF directly bound to an AAAG motif in the promoter of CsGS2, and promotes its activity. The study shed new light on the molecular mechanism by which CsDOF activates CsGS2 gene expression and contributes to glutamine biosynthesis in tea plants.

The apple DNA-binding one zinc-finger protein MdDof54 promotes drought resistance

DNA-binding one zinc-finger (Dof) proteins constitute a family of transcription factors with a highly conserved Dof domain that contains a C2C2 zinc-finger motif. Although several studies have demonstrated that Dof proteins are involved in multiple plant processes, including development and stress resistance, the functions of these proteins in drought stress resistance are largely unknown. Here, we report the identification of the MdDof54 gene from apple and document its positive roles in apple drought resistance. After long-term drought stress, compared with nontransgenic plants, MdDof54 RNAi plants had significantly shorter heights and weaker root systems; the transgenic plants also had lower shoot and root hydraulic conductivity, as well as lower photosynthesis rates. By contrast, compared with nontransgenic plants, MdDof54-overexpressing plants had higher photosynthesis rates and shoot hydraulic conductivity under long-term drought stress. Moreover, compared with nontransgenic plants, MdDof54-overexpressing plants had higher survival percentages under short-term drought stress, whereas MdDof54 RNAi plants had lower survival percentages. MdDof54 RNAi plants showed significant downregulation of 99 genes and significant upregulation of 992 genes in response to drought, and 366 of these genes were responsive to drought. We used DAP-seq and ChIP-seq analyses to demonstrate that MdDof54 recognizes cis-elements that contain an AAAG motif. Taken together, our results provide new information on the functions of MdDof54 in plant drought stress resistance as well as resources for apple breeding aimed at the improvement of drought resistance.

Genome-wide identification and evolution of Dof transcription factor family in cultivated and ancestral cotton species

The DNA-binding with one finger (Dof) proteins are transcription factors involved in many biological processes in plants. To predict the evolutionary pattern, a genome-wide in-silico analysis of Dof TFs family in diploid (Gossypium arboreum and Gossypium raimondii) and allotetraploid (Gossypium hirsutum and Gossypium barbadense) cotton species were carried out. In G. arboreum, we have identified 58 non-redundant genes encoding Dof proteins renamed as GaDof (G. arboreum Dof), 55 Dof genes were identified in G. raimondii (GrDof), 89 were predicted ffrom G. hirsutum (GhDof) and the highest, 110 Dof genes were identified in G. barbadense (GbDof). The phylogenetic analysis, physical location, gene structure, conserved domain analyses were also investigated for G. arboreum, G. raimondii, and G. hirsutum. The gene expression pattern in G. hirsutum, at different growth stages, revealing the probable involvement of some GhDof genes in growth and development. These genes may improve seed germination and growth in cotton.

CDF transcription factors: plant regulators to deal with extreme environmental conditions

In terrestrial environments, water and nutrient availabilities and temperature conditions are highly variable, and especially in extreme environments limit survival, growth, and reproduction of plants. To sustain growth and maintain cell integrity under unfavourable environmental conditions, plants have developed a variety of biochemical and physiological mechanisms, orchestrated by a large set of stress-responsive genes and a complex network of transcription factors. Recently, cycling DOF factors (CDFs), a group of plant-specific transcription factors (TFs), were identified as components of the transcriptional regulatory networks involved in the control of abiotic stress responses. The majority of the members of this TF family are activated in response to a wide range of adverse environmental conditions in different plant species. CDFs regulate different aspects of plant growth and development such as photoperiodic flowering-time control and root and shoot growth. While most of the functional characterization of CDFs has been reported in Arabidopsis, recent data suggest that their diverse roles extend to other plant species. In this review, we integrate information related to structure and functions of CDFs in plants, with special emphasis on their role in plant responses to adverse environmental conditions.

Transcription factor CDF4 promotes leaf senescence and floral organ abscission by regulating abscisic acid and reactive oxygen species pathways in Arabidopsis

Leaf senescence is a highly complex developmental process that is tightly controlled by multiple layers of regulation. Abscisic acid (ABA) and reactive oxygen species (ROS) are two well-known factors that promote leaf senescence. We show here that the transcription factor CDF4 positively regulates leaf senescence. Constitutive and inducible overexpression of CDF4 accelerates leaf senescence, while knockdown of CDF4 delays it. CDF4 increases endogenous ABA levels by upregulating the transcription of the ABA biosynthesis genes 9-cis-epoxycarotenoid dioxygenase 2, 3 (NCED2, 3) and suppresses H₂ O₂ scavenging by repressing expression of the catalase2 (CAT2) gene. NCED2, 3 knockout and CAT2 overexpression partially rescue premature leaf senescence caused by CDF4 overexpression. We also show that CDF4 promotes floral organ abscission by activating the polygalacturonase PGAZAT gene. Based on these results, we propose that the levels of CDF4, ABA, and ROS undergo a gradual increase driven by their interlinking positive feedback loops during the leaf senescence and floral organ abscission processes.

The DOF Transcription Factors in Seed and Seedling Development

The DOF (DNA binding with one finger) family of plant-specific transcription factors (TF) was first identified in maize in 1995. Since then, DOF proteins have been shown to be present in the whole plant kingdom, including the unicellular alga Chlamydomonas reinhardtii. The DOF TF family is characterised by a highly conserved DNA binding domain (DOF domain), consisting of a CX₂C-X₂₁-CX₂C motif, which is able to form a zinc finger structure. Early in the study of DOF proteins, their relevance for seed biology became clear. Indeed, the PROLAMIN BINDING FACTOR (PBF), one of the first DOF proteins characterised, controls the endosperm-specific expression of the zein genes in maize. Subsequently, several DOF proteins from both monocots and dicots have been shown to be primarily involved in seed development, dormancy and germination, as well as in seedling development and other light-mediated processes. In the last two decades, the molecular network underlying these processes have been outlined, and the main molecular players and their interactions have been identified. In this review, we will focus on the DOF TFs involved in these molecular networks, and on their interaction with other proteins.

A Jasmonate-Activated MYC2-Dof2.1-MYC2 Transcriptional Loop Promotes Leaf Senescence in Arabidopsis

DNA binding-with-one-finger (Dof) proteins are plant-specific transcription factors closely associated with a variety of physiological processes. Here, we show that the Dof protein family in Arabidopsis (Arabidopsis thaliana) functions in leaf senescence. Disruption of Dof2 1, a jasmonate (JA)-inducible gene, led to a marked reduction in promotion of leaf senescence and inhibition of root development as well as dark-induced and age-dependent leaf senescence, while overexpression of Dof2 1 promoted these processes. Additionally, the dof2 1 knockout mutant showed almost no change in the transcriptome in the absence of JA; in the presence of JA, expression of many senescence-associated genes, including MYC2, which encodes a central regulator of JA responses, was induced to a lesser extent in the dof2 1 mutant than in the wild type. Furthermore, direct activation of the MYC2 promoter by Dof2.1, along with the results of epistasis analysis, indicated that Dof2.1 enhances leaf senescence mainly by promoting MYC2 expression. Interestingly, MYC2 was also identified as a transcriptional activator responsible for JA-inducible expression of Dof2 1 Based on these results, we propose that Dof2.1 acts as an enhancer of JA-induced leaf senescence through the MYC2-Dof2.1-MYC2 feedforward transcriptional loop.

Re-evaluation of the ethylene-dependent and -independent pathways in the regulation of floral and organ abscission

Abscission is a developmental process with important implications for agricultural practices. Ethylene has long been considered as a key regulator of the abscission process. The existence of an ethylene-independent abscission pathway, controlled by the complex of INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) peptide and the HAESA (HAE) and HAESA-like2 (HSL2) kinases, has been proposed, based mainly on observations that organ abscission in ethylene-insensitive mutants was delayed but not inhibited. A recent review on plant organ abscission signaling highlighted the IDA-HAE-HSL2 components as the regulators of organ abscission, while the role of auxin and ethylene in this process was hardly addressed. After a careful analysis of the relevant abscission literature, we propose that the IDA-HAE-HSL2 pathway is essential for the final stages of organ abscission, while ethylene plays a major role in its initiation and progression. We discuss the view that the IDA-HAE-HSL2 pathway is ethylene independent, and present recent evidence showing that ethylene activates the IDA-HAE-HSL2 complex. We conclude that the ability of an organ to abscise is tightly linked to cell turgidity in the abscission zone, and suggest that lack of cell turgidity might contribute to the failure of floral organ abscission in the ida mutants.

Genome-wide identification and comparative evolutionary analysis of the Dof transcription factor family in physic nut and castor bean

DNA-binding with one finger (Dof) proteins comprise a plant-specific transcription factor family involved in plant growth, development and stress responses. This study presents a genome-wide comparison of Dof family genes in physic nut (Jatropha curcas) and castor bean (Ricinus communis), two Euphorbiaceae plants that have not experienced any recent whole-genome duplication. A total of 25 or 24 Dof genes were identified from physic nut and castor genomes, respectively, where JcDof genes are distributed across nine out of 11 chromosomes. Phylogenetic analysis assigned these genes into nine groups representing four subfamilies, and 24 orthologous groups were also proposed based on comparison of physic nut, castor, Arabidopsis and rice Dofs. Conserved microsynteny was observed between physic nut and castor Dof-coding scaffolds, which allowed anchoring of 23 RcDof genes to nine physic nut chromosomes. In contrast to how no recent duplicate was present in castor, two tandem duplications and one gene loss were found in the Dof gene family of physic nut. Global transcriptome profiling revealed diverse patterns of Jc/RcDof genes over various tissues, and key Dof genes involved in flower development and stress response were also identified in physic nut. These findings provide valuable information for further studies of Dof genes in physic nut and castor.

Genomic dissection of pod shattering in common bean: mutations at non-orthologous loci at the basis of convergent phenotypic evolution under domestication of leguminous species

The complete or partial loss of shattering ability occurred independently during the domestication of several crops. Therefore, the study of this trait can provide an understanding of the link between phenotypic and molecular convergent evolution. The genetic dissection of 'pod shattering' in Phaseolus vulgaris is achieved here using a population of introgression lines and next-generation sequencing techniques. The 'occurrence' of the indehiscent phenotype (indehiscent versus dehiscent) depends on a major locus on chromosome 5. Furthermore, at least two additional genes are associated with the 'level' of shattering (number of shattering pods per plant: low versus high) and the 'mode' of shattering (non-twisting versus twisting pods), with all of these loci contributing to the phenotype by epistatic interactions. Comparative mapping indicates that the major gene identified on common bean chromosome 5 corresponds to one of the four quantitative trait loci for pod shattering in Vigna unguiculata. None of the loci identified comprised genes that are homologs of the known shattering genes in Glycine max. Therefore, although convergent domestication can be determined by mutations at orthologous loci, this was only partially true for P. vulgaris and V. unguiculata, which are two phylogenetically closely related crop species, and this was not the case for the more distant P. vulgaris and G. max. Conversely, comparative mapping suggests that the convergent evolution of the indehiscent phenotype arose through mutations in different genes from the same underlying gene networks that are involved in secondary cell-wall biosynthesis and lignin deposition patterning at the pod level.

Multifaceted Role of PheDof12-1 in the Regulation of Flowering Time and Abiotic Stress Responses in Moso Bamboo (Phyllostachys edulis)

DNA binding with one finger (Dof) proteins, forming an important transcriptional factor family, are involved in gene transcriptional regulation, development, stress responses, and flowering responses in annual plants. However, knowledge of Dofs in perennial and erratically flowering moso bamboo is limited. In view of this, a Dof gene, PheDof12-1, was isolated from moso bamboo. PheDof12-1 is located in the nucleus and has the highest expression in palea and the lowest in bract. Moreover, PheDof12-1 expression is high in flowering leaves, then declines during flower development. The transcription level of PheDof12-1 is highly induced by cold, drought, salt, and gibberellin A3 (GA₃) stresses. The functional characteristics of PheDof are researched for the first time in Arabidopsis, and the results show that transgenic Arabidopsis overexpressing PheDof12-1 shows early flowering under long-day (LD) conditions but there is no effect on flowering time under short-day (SD) conditions; the transcription levels of FT, SOC1, and AGL24 are upregulated; and FLC and SVP are downregulated. PheDof12-1 exhibits a strong diurnal rhythm, inhibited by light treatment and induced in dark. Yeast one-hybrid (Y1H) assay shows that PheDof12-1 can bind to the promoter sequence of PheCOL4. Taken together, these results indicate that PheDof12-1 might be involved in abiotic stress and flowering time, which makes it an important candidate gene for studying the molecular regulation mechanisms of moso bamboo flowering.

Quantitative Analysis of Floral Organ Abscission in Arabidopsis Via a Petal Breakstrength Assay

Petal breakstrength (pBS) is a method to study floral organ abscission by quantitating the force required to pull a petal from the receptacle. However, it is only well established in some labs and used in a subset of abscission studies. Here, we describe the mechanism and operation of the pBS meter, as well as detailed measurement and further data analysis. We show that it is a powerful tool to detect early or delayed floral organ abscission in mutant or transgenic plants, which is not easily detected by phenotypic investigation.

Identification of MdDof genes in apple and analysis of their response to biotic or abiotic stress

As a classic plant-specific transcription factor family - the Dof domain proteins - are involved in a variety of biological processes in organisms ranging from unicellular Chlamydomonas to higher plants. However, there are limited reports of MdDof (Malus domestica Borkh. DNA-binding One Zinc Finger) domain proteins in fruit trees, especially in apple. In this study we identified 54 putative Dof transcription factors in the apple genome. We analysed the gene structures, protein motifs, and chromosome locations of each of the MdDof genes. Next, we characterised all 54 MdDofs their expression patterns under different abiotic and biotic stress conditions. It was found that MdDof6,26 not only played an important role in the biotic/abiotic stress but may also be involved in many molecular functions. Further, both in flower development and pollen tube growth it was found that the relative expression of MdDof24 increased rapidly, also with gene ontology analysis it was indicated that MdDof24 was involved in the chemical reaction and flower development pathways. Taken together, our results provide useful clues as to the function of MdDof genes in apple and serve as a reference for studies of Dof zinc finger genes in other plants.

Advances in abscission signaling

Abscission is a process in plants for shedding unwanted organs such as leaves, flowers, fruits, or floral organs. Shedding of leaves in the fall is the most visually obvious display of abscission in nature. The very shape plants take is forged by the processes of growth and abscission. Mankind manipulates abscission in modern agriculture to do things such as prevent pre-harvest fruit drop prior to mechanical harvesting in orchards. Abscission occurs specifically at abscission zones that are laid down as the organ that will one day abscise is developed. A sophisticated signaling network initiates abscission when it is time to shed the unwanted organ. In this article, we review recent advances in understanding the signaling mechanisms that activate abscission. Physiological advances and roles for hormones in abscission are also addressed. Finally, we discuss current avenues for basic abscission research and potentially lucrative future directions for its application to modern agriculture.

The Tomato Hybrid Proline-rich Protein regulates the abscission zone competence to respond to ethylene signals

The Tomato Hybrid Proline-rich Protein (THyPRP) gene was specifically expressed in the tomato (Solanum lycopersicum) flower abscission zone (FAZ), and its stable antisense silencing under the control of an abscission zone (AZ)-specific promoter, Tomato Abscission Polygalacturonase4, significantly inhibited tomato pedicel abscission following flower removal. For understanding the THyPRP role in regulating pedicel abscission, a transcriptomic analysis of the FAZ of THyPRP-silenced plants was performed, using a newly developed AZ-specific tomato microarray chip. Decreased expression of THyPRP in the silenced plants was already observed before abscission induction, resulting in FAZ-specific altered gene expression of transcription factors, epigenetic modifiers, post-translational regulators, and transporters. Our data demonstrate that the effect of THyPRP silencing on pedicel abscission was not mediated by its effect on auxin balance, but by decreased ethylene biosynthesis and response. Additionally, THyPRP silencing revealed new players, which were demonstrated for the first time to be involved in regulating pedicel abscission processes. These include: gibberellin perception, Ca²⁺-Calmodulin signaling, Serpins and Small Ubiquitin-related Modifier proteins involved in post-translational modifications, Synthaxin and SNARE-like proteins, which participate in exocytosis, a process necessary for cell separation. These changes, occurring in the silenced plants early after flower removal, inhibited and/or delayed the acquisition of the competence of the FAZ cells to respond to ethylene signaling. Our results suggest that THyPRP acts as a master regulator of flower abscission in tomato, predominantly by playing a role in the regulation of the FAZ cell competence to respond to ethylene signals.

A Profusion of Molecular Scissors for Pectins: Classification, Expression, and Functions of Plant Polygalacturonases

In plants, the construction, differentiation, maturation, and degradation of the cell wall are essential for development. Pectins, which are major constituents of primary cell walls in eudicots, function in multiple developmental processes through their synthesis, modification, and degradation. Several pectin modifying enzymes regulate pectin degradation via different modes of action. Polygalacturonases (PGs), which function in the last step of pectin degradation, are a crucial class of pectin-modifying enzymes. Based on differences in their hydrolyzing activities, PGs can be divided into three main types: exo-PGs, endo-PGs, and rhamno-PGs. Their functions were initially investigated based on the expression patterns of PG genes and measurements of total PG activity in organs. In most plant species, PGs are encoded by a large, multigene family. However, due to the lack of genome sequencing data in early studies, the number of identified PG genes was initially limited. Little was initially known about the evolution and expression patterns of PG family members in different species. Furthermore, the functions of PGs in cell dynamics and developmental processes, as well as the regulatory pathways that govern these functions, are far from fully understood. In this review, we focus on how recent studies have begun to fill in these blanks. On the basis of identified PG family members in multiple species, we review their structural characteristics, classification, and molecular evolution in terms of plant phylogenetics. We also highlight the diverse expression patterns and biological functions of PGs during various developmental processes, as well as their mechanisms of action in cell dynamic processes. How PG functions are potentially regulated by hormones, transcription factors, environmental factors, pH and Ca²⁺ is discussed, indicating directions for future research into PG function and regulation.

Evolution analysis of Dof transcription factor family and their expression in response to multiple abiotic stresses in Malus domestica

As a family of transcription factors, DNA binding with one figure (Dof) proteins play important roles in various biological processes in plants. Here, a total of 60 putative apple (Malus domestica) Dof genes (MdDof) were identified and mapped to different chromosomes. Chromosomal distribution and synteny analysis indicated that the expansion of the MdDof genes came primarily from segmental and duplication events, and from whole genome duplication, which lead to more Dof members in apples than in other plants. All 60 MdDof genes were classified into thirteen groups, according to multiple sequence alignment and the phylogenetic tree constructed of Dof genes from apple, peach (Prunus persica), Arabidopsis and rice. Within each group, the members shared a similar exon/intron and motif compositions, although the sizes of the MdDof genes and encoding proteins were quite different. Several Dof genes from the apple and peach were identified to be homologues based on their close synteny relationship, which suggested that these genes bear similar functions. Half of the MdDof genes were randomly selected to determine their responses to different stresses. The majority of MdDof genes were quite sensitive to PEG, NaCl, cold and exogenous ABA treatment. Our results suggested that MdDof family members may play important roles in plant tolerance to abiotic stress.

Identification and functional prediction of stress responsive AP2/ERF transcription factors in Brassica napus by genome-wide analysis

Using homology and domain authentication, 321 putative AP2/ERF transcription factors were identified in Brassica napus, called BnAP2/ERF TFs. BnAP2/ERF TFs were classified into five major subfamilies, including DREB, ERF, AP2, RAV, and BnSoloist. This classification is based on phylogenetic analysis, motif identification, gene structure analysis, and physiochemical characterization. These TFs were annotated based on phylogenetic relationship with Brassica rapa. BnAP2/ERF TFs were located on 19 chromosomes of B. napus. Orthologs and paralogs were identified using synteny-based methods Ks calculation within B. napus genome and between B. napus with other species such as B. rapa, Brassica oleracea, and Arabidopsis thaliana indicated that BnAP2/ERF TFs were formed through duplication events occurred before B. napus formation. Kn/Ks values were between 0 and 1, suggesting the purifying selection among BnAP2/ERF TFs. Gene ontology annotation, cis-regulatory elements and functional interaction networks suggested that BnAP2/ERF TFs participate in response to stressors, including drought, high salinity, heat and cold as well as developmental processes particularly organ specification and embryogenesis. The identified cis-regulatory elements in the upstream of BnAP2/ERF TFs were responsive to abscisic acid. Analysis of the expression data derived from Illumina Hiseq 2000 RNA sequencing revealed that BnAP2/ERF genes were highly expressed in the roots comparing to flower buds, leaves, and stems. Also, the ERF subfamily was over-expressed under salt and fungal treatments. BnERF039 and BnERF245 are candidates for salt-tolerant B. napus. BnERF253-256 and BnERF260-277 are potential cytokinin response factors. BnERF227, BnERF228, BnERF234, BnERF134, BnERF132, BnERF176, and BnERF235 were suggested for resistance against Leptosphaeria maculan and Leptosphaeria biglobosa.

ZmDof30 Negatively Regulates the Promoter Activity of the Pollen-Specific Gene Zm908

The maize (Zea mays) pollen-predominant gene Zm908, a novel small-peptide gene, was reported to play critical roles in pollen germination and pollen tube growth in our previous work. In this study, we aimed to explore the regulatory mechanism of Zm908. The putative promoter of Zm908 was cloned and analyzed. The activity analysis of a series of promoter truncations in different tissues of transgenic tobacco plants indicated that the Zm908 promoter is pollen-specific and that the -126 to -68 region is crucial for pollen expression. The 5' deletion analysis of the -126 to -68 region revealed that the -126 to -102 region functions as a transcriptional suppression element. ZmDof30, which is predominantly expressed in pollen and whole anthers, was cloned and characterized. ZmDof30-GFP localized to the nuclei of maize protoplasts and possessed no transcriptional activation activity in a yeast system. ZmDof30 could bind to the AAAG elements in p184 sequence containing the -126 to +58 region of the Zm908 promoter in vitro and in vivo, and negatively regulated p184 activity in tobacco leaves. Collectively, ZmDof30 may function as a Zm908 transcriptional repressor in pollen, and these results may provide a better understanding of the regulation of the Zm908 gene. Additionally, the pollen-specific Zm908 promoter may be valuable for genetically engineering male sterility.

A Novel Soybean ERF Transcription Factor, GmERF113, Increases Resistance to Phytophthora sojae Infection in Soybean

Phytophthora root and stem rot of soybean caused by the oomycete Phytophthora sojae, is a destructive disease worldwide. Ethylene response factors (ERFs) play important roles in regulating plant biotic and abiotic stress tolerance. In this study, a new ERF gene, GmERF113, was isolated from the highly resistant soybean 'Suinong 10.' Sequence analysis suggested that the protein encoded by GmERF113 contained a conserved AP2/ERF domain of 58 amino acid and belonged to the B-4 subgroup of the ERF subfamily. Expression of GmERF113 was significantly induced by P. sojae, ethylene, and methyl jasmonate. GmERF113 protein localized to the nucleus when transiently expressed in Arabidopsis protoplasts, could bind to the GCC-box, and acted as a transcription activator. In addition, a region of the full-length GmERF113, GmERF113-II, interacted with a basic helix-loop-helix transcription factor (GmbHLH) in yeast cells. Full-length GmERF113 also interacted with GmbHLH in planta. GmERF113-overexpressing transgenic plants in susceptible cultivar 'Dongnong 50' soybean exhibited increased resistance to P. sojae and positively regulated the expression of the pathogenesis-related genes, PR1 and PR10-1. These results indicate that GmERF113 may play a crucial role in the defense of soybean against P. sojae infection.

Transcriptome-Based Analysis of Dof Family Transcription Factors and Their Responses to Abiotic Stress in Tea Plant (Camellia sinensis)

Tea plant (Camellia sinensis (L.) O. Kuntze) is affected by abiotic stress during its growth and development. DNA-binding with one finger (Dof) transcription factors (TFs) play important roles in abiotic stress tolerance of plants. In this study, a total of 29 putative Dof TFs were identified based on transcriptome of tea plant, and the conserved domains and common motifs of these CsDof TFs were predicted and analyzed. The 29 CsDof proteins were divided into 7 groups (A, B1, B2, C1, C2.1, C2.2, and D2), and the interaction networks of Dof proteins in C. sinensis were established according to the data in Arabidopsis. Gene expression was analyzed in “Yingshuang” and “Huangjinya” under four experimental stresses by qRT-PCR. CsDof genes were expressed differentially and related to different abiotic stress conditions. In total, our results might suggest that there is a potential relationship between CsDof factors and tea plant stress resistance.

Genome-wide analysis of the DNA-binding with one zinc finger (Dof) transcription factor family in bananas

DNA-binding with one finger (Dof) domain proteins are a multigene family of plant-specific transcription factors involved in numerous aspects of plant growth and development. In this study, we report a genome-wide search for Musa acuminata Dof (MaDof) genes and their expression profiles at different developmental stages and in response to various abiotic stresses. In addition, a complete overview of the Dof gene family in bananas is presented, including the gene structures, chromosomal locations, cis-regulatory elements, conserved protein domains, and phylogenetic inferences. Based on the genome-wide analysis, we identified 74 full-length protein-coding MaDof genes unevenly distributed on 11 chromosomes. Phylogenetic analysis with Dof members from diverse plant species showed that MaDof genes can be classified into four subgroups (StDof I, II, III, and IV). The detailed genomic information of the MaDof gene homologs in the present study provides opportunities for functional analyses to unravel the exact role of the genes in plant growth and development.

The transcription factor SlDof22 involved in ascorbate accumulation and salinity stress in tomato

Ascorbic acid (AsA) is an important antioxidant and its biosynthesis in plants has extensively been investigated. However, the key regulatory factors controlling the accumulation of AsA remain elusive. Here we report that tomato SlDof22, a member of the Dof family, negatively regulated AsA accumulation in tomato. RNA interference (RNAi) of SlDof22 in transgenic lines induced AsA levels, and affected the expression of genes in the D-mannose/L-galactose pathway and AsA recycling. In addition, SlSOS1 was significantly down-regulated in SlDof22 RNAi plants which resulted in reduced tolerance to salt stress. We further found that SlDof22 could bind to the promoter sequence of SlSOS1 gene by yeast one-hybrid analysis. Taken together, our data suggested that the Dof transcription factor SIDof22 involved in ascorbate accumulation and salt stress response in tomato.

The banana fruit Dof transcription factor MaDof23 acts as a repressor and interacts with MaERF9 in regulating ripening-related genes

The DNA binding with one finger (Dof) proteins, a family of plant-specific transcription factors, are involved in a variety of plant biological processes. However, little information is available on their involvement in fruit ripening. We have characterized 25 MaDof genes from banana fruit (Musa acuminata), designated as MaDof1-MaDof25 Gene expression analysis in fruit subjected to different ripening conditions revealed that MaDofs were differentially expressed during different stages of ripening. MaDof10, 23, 24, and 25 were ethylene-inducible and nuclear-localized, and their transcript levels increased during fruit ripening. Moreover, yeast two-hybrid and bimolecular fluorescence complementation analyses demonstrated a physical interaction between MaDof23 and MaERF9, a potential regulator of fruit ripening reported in a previous study. We determined that MaDof23 is a transcriptional repressor, whereas MaERF9 is a transcriptional activator. We suggest that they might act antagonistically in regulating 10 ripening-related genes, including MaEXP1/2/3/5, MaXET7, MaPG1, MaPME3, MaPL2, MaCAT, and MaPDC, which are associated with cell wall degradation and aroma formation. Taken together, our findings provide new insight into the transcriptional regulation network controlling banana fruit ripening.

Are We on the Right Track: Can Our Understanding of Abscission in Model Systems Promote or Derail Making Improvements in Less Studied Crops?

As the world population grows and resources and climate conditions change, crop improvement continues to be one of the most important challenges for agriculturalists. The yield and quality of many crops is affected by abscission or shattering, and environmental stresses often hasten or alter the abscission process. Understanding this process can not only lead to genetic improvement, but also changes in cultural practices and management that will contribute to higher yields, improved quality and greater sustainability. As plant scientists, we have learned significant amounts about this process through the study of model plants such as Arabidopsis, tomato, rice, and maize. While these model systems have provided significant valuable information, we are sometimes challenged to use this knowledge effectively as variables including the economic value of the crop, the uniformity of the crop, ploidy levels, flowering and crossing mechanisms, ethylene responses, cultural requirements, responses to changes in environment, and cellular and tissue specific morphological differences can significantly influence outcomes. The value of genomic resources for lesser-studied crops such as cranberries and grapes and the orphan crop fonio will also be considered.

The Transcription Factor AtDOF4.7 Is Involved in Ethylene- and IDA-Mediated Organ Abscission in Arabidopsis

Organ abscission is an important plant developmental process that occurs in response to environmental stress or pathogens. In Arabidopsis, ligand signals, such as ethylene or INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), can regulate organ abscission. Previously, we reported that overexpression of AtDOF4.7, a transcription factor gene, directly suppresses the expression of the abscission-related gene ARABIDOPSIS DEHISCENCE ZONE POLYGALACTURONASE 2 (ADPG2), resulting in a deficiency of floral organ abscission. However, the relationship between AtDOF4.7 and abscission pathways still needs to be investigated. In this study, we showed that ethylene regulates the expression of AtDOF4.7, and the peptide ligand, IDA negatively regulates AtDOF4.7 at the transcriptional level. Genetic evidence indicates that AtDOF4.7 and IDA are involved in a common pathway, and a MAPK cascade can phosphorylate AtDOF4.7 in vitro. Further in vivo data suggest that AtDOF4.7 protein levels may be regulated by this phosphorylation. Collectively, our results indicate that ethylene regulates AtDOF4.7 that is involved in the IDA-mediated floral organ abscission pathway.

Genome-Wide Identification and Expression Profile of Dof Transcription Factor Gene Family in Pepper (Capsicum annuum L.)

Dof (DNA-binding One Zinc Finger) transcription factor family is unique to plants and has diverse roles associated with plant-specific phenomena, such as light, phytohormone and defense responses as well as seed development and germination. Although, genome-wide analysis of this family has been performed in many species, information regarding Dof genes in the pepper, Capsicum annuum L., is extremely limited. In this study, exhaustive searches of pepper genome revealed 33 potential CaDofs that were phylogenetically clustered into four subgroups. Twenty-nine of the 33 Dof genes could be mapped on 11 chromosomes, except for chromosome 7. The intron/exon organizations and conserved motif compositions of these genes were also analyzed. Additionally, phylogenetic analysis and classification of the Dof transcription factor family in eight plant species revealed that S. lycopersicum and C. annuum as well as O. sativa and S. bicolor Dof proteins may have evolved conservatively. Moreover, comprehensive expression analysis of CaDofs using a RNA-seq atlas and quantitative real-time polymerase chain reaction (qRT-PCR) revealed that these genes exhibit a variety of expression patterns. Most of the CaDofs were expressed in at least one of the tissues tested, whereas several genes were identified as being highly responsive to heat and salt stresses. Overall, this study describes the first genome-wide analysis of the pepper Dof family, whose genes exhibited different expression patterns in all primary fruit developmental stages and tissue types, as in response to abiotic stress. In particular, some Dof genes might be used as biomarkers for heat and salt stress. The results could expand our understanding of the roles of Dof genes in pepper.