Histone deacetylase HD2 interacts with ERF1 and is involved in longan fruit senescence

Phosphorylation of MdWRKY70L by MdMPK6/02G mediates reactive oxygen accumulation to regulate apple fruit senescence

Apple (Malus domestica Borkh.) is a globally significant crop and a vital dietary component worldwide. During ripening, apples exhibit a longitudinal gradient, ripening first at the stalk cavity and extending towards the calyx concave. When the fruit is harvested at the right time or later, the stalk cavity of many varieties often shows over-ripening, that is, premature senescence such as peel browning, which diminishes fruit quality. This study examines the natural senescence process in 6-year-old 'Ruixue' apples by screening transcriptome data to uncover senescence-related genes and validate their molecular functions. Our analysis of antioxidant capacity and reactive oxygen species (ROS) in different peel regions revealed that malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide anion (O 2 - ⋅ ) levels increased with senescence, where ROS-scavenging enzyme activity was notably reduced, especially in the stalk cavity (compared with the fruits in the stalk cavity at 120 days, the activities of SOD, POD, and CAT in stalk cavity of fruits at 205 days were significantly decreased in 65.4%, 82.7%, and 91.1%, respectively). Transcriptome clustering and enrichment analyses across developmental stages revealed MdWRKY70L, MdSAG101, and MdZAT12 as key regulators of peel senescence. MdWRKY70L could interact with MdSAG101/MdZAT12 both in vivo and in vitro, thereby mediating ROS accumulation in the peel and accelerating the fruit senescence process. Further in vitro and in vivo studies demonstrated that MdWRKY70L is phosphorylated at Ser199 by MdMPK6/02G, enhancing MdWRKY70L protein stability and promoting peel senescence. These findings offer insights for developing strategies to delay fruit senescence and improve postharvest quality control.

Involvement of ethylene production and polyamines in rind pitting of 'Fino' lemon fruit

Rind disorders in early cultivars of lemon fruits cause serious economic losses at market since these lemons are very sensitive to develop rind pitting during postharvest. Therefore, the aim of this study was to determine the involvement of ethylene and polyamines (PAs) in rind pitting of 'Fino' lemons grown with an intensive fertigation (IF) and standard fertigation (SF). Results after degreening treatment showed that lemons harvested from the IF system had ca. 48 %, 3.5-fold, 2.5-fold and 28 % more respiration rate, ethylene production, free and total 1-aminocyclopropane-1-carboxylic acid (ACC), respectively, than SF lemons. Furthermore, the concentrations of spermidine and spermine were ca. 30 % lower in IF lemons compared to SF ones, without differences in putrescine levels. After 7 days of storage at 8 °C, the highest values of rind pitting incidence and severity of damage were found in IF lemons. It was observed that lemons with rind pitting harvested from the IF system had the highest concentration of free-ACC and total-ACC, whereas the spermine content was ca. 3-fold higher in fruits without rind pitting independently of the fertigation system. Thus, the results showed that ethylene can be considered as a marker for the lemon fruit susceptibility to suffer rind pitting, while PAs have a protective role.

Ethylene biosynthesis and signal transduction during ripening and softening in non-climacteric fruits: an overview

In recent years, the ethylene-mediated ripening and softening of non-climacteric fruits have been widely mentioned. In this paper, recent research into the ethylene-mediated ripening and softening of non-climacteric fruits is summarized, including the involvement of ethylene biosynthesis and signal transduction. In addition, detailed studies on how ethylene interacts with other hormones to regulate the ripening and softening of non-climacteric fruits are also reviewed. These findings reveal that many regulators of ethylene biosynthesis and signal transduction are linked with the ripening and softening of non-climacteric fruits. Meanwhile, the perspectives of future research on the regulation of ethylene in non-climacteric fruit are also proposed. The overview of the progress of ethylene on the ripening and softening of non-climacteric fruit will aid in the identification and characterization of key genes associated with ethylene perception and signal transduction during non-climacteric fruit ripening and softening.

MaNAC029 modulates ethylene biosynthesis and fruit quality and undergoes MaXB3-mediated proteasomal degradation during banana ripening

INTRODUCTIONS

Ethylene regulates ripening by activating various metabolic pathways that controlcolor, aroma, flavor, texture, and consequently, the quality of fruits. However, the modulation of ethylene biosynthesis and quality formation during banana fruit ripening remains unclear.

OBJECTIVES

The present study aimed to identify the regulatory module that regulates ethylene and fruit quality-related metabolisms during banana fruit ripening.

METHODS

We used RNA-seq to compare unripe and ripe banana fruits and identified a ripening-induced NAC transcription factor, MaNAC029. We further performed DNA affinity purification sequencing to identify the MaNAC029's target genes involved in ethylene biosynthesis and fruit quality formation, and electrophoretic mobility shift assay, chromatin immunoprecipitation with real-time polymerase chain reaction and dual luciferase assays to explore the underlying regulatory mechanisms. Immunoprecipitation combined with mass spectrometry, yeast two-hybrid assay, and bimolecular fluorescence complementation assay were used to screen and verify the proteins interacting with MaNAC029. Finally, the function of MaNAC029 and its interacting protein associated with ethylene biosynthesis and quality formation was verified through transient overexpression experiments in banana fruits.

RESULTS

The study identified a nucleus-localized, ripening-induced NAC transcription factor MaNAC029. It transcriptionally activated genes associated with ethylene biosynthesis and a variety of cellular metabolisms related to fruit quality formation (cell wall degradation, starch degradation, aroma compound synthesis, and chlorophyll catabolism) by directly modulating their promoter activity during ripening. Overexpression of MaNAC029 in banana fruits activated ethylene biosynthesis and accelerated fruit ripening and quality formation. Notably, the E3 ligase MaXB3 interacted with and ubiquitinated MaNAC029 protein, facilitating MaNAC029 proteasomal degradation. Consistent with this finding, MaXB3 overexpression attenuated MaNAC029-enhanced ethylene biosynthesis and quality formation.

CONCLUSION

Our findings demonstrate that a MaXB3-MaNAC029 module regulates ethylene biosynthesis and a series of cellular metabolisms related to fruit quality formation during banana ripening. These results expand the understanding of the transcriptional and post-translational mechanisms of fruit ripening and quality formation.

Genome-Wide Identification of Histone Deacetylases and Their Roles Related with Light Response in Tartary Buckwheat (Fagopyrum tataricum)

Histone deacetylases (HDACs), known as histone acetylation erasers, function crucially in plant growth and development. Although there are abundant reports focusing on HDACs of Arabidopsis and illustrating their important roles, the knowledge of HDAC genes in Tartary buckwheat (Polygonales Polygonaceae Fagopyrum tataricum (L.) Gaertn) is still scarce. In the study, a total of 14 HDAC genes were identified and divided into three main groups: Reduced Potassium Dependency-3/His-52 tone Deacetylase 1 (RPD3/HDA1), Silent Information Regulator 2 (SIR2), and the plant-53 specific HD2. Domain and motif composition analysis showed there were conserved domains and motifs in members from the same subfamilies. The 14 FtHDACs were distributed asymmetrically on 7 chromosomes, with three segmental events and one tandem duplication event identified. The prediction of the cis-element in promoters suggested that FtHDACs probably acted in numerous biological processes including plant growth, development, and response to environmental signals. Furthermore, expression analysis based on RNA-seq data displayed that all FtHDAC genes were universally and distinctly expressed in diverse tissues and fruit development stages. In addition, we found divergent alterations in FtHDACs transcript abundance in response to different light conditions according to RNA-seq and RT-qPCR data, indicating that five FtHDACs might be involved in light response. Our findings could provide fundamental information for the HDAC gene family and supply several targets for future function analysis of FtHDACs related with light response of Tartary buckwheat.

A petunia transcription factor, PhOBF1, regulates flower senescence by modulating gibberellin biosynthesis

Flower senescence is commonly enhanced by the endogenous hormone ethylene and suppressed by the gibberellins (GAs) in plants. However, the detailed mechanisms for the antagonism of these hormones during flower senescence remain elusive. In this study, we characterized one up-regulated gene PhOBF1, belonging to the basic leucine zipper transcription factor family, in senescing petals of petunia (Petunia hybrida). Exogenous treatments with ethylene and GA3 provoked a dramatic increase in PhOBF1 transcripts. Compared with wild-type plants, PhOBF1-RNAi transgenic petunia plants exhibited shortened flower longevity, while overexpression of PhOBF1 resulted in delayed flower senescence. Transcript abundances of two senescence-related genes PhSAG12 and PhSAG29 were higher in PhOBF1-silenced plants but lower in PhOBF1-overexpressing plants. Silencing and overexpression of PhOBF1 affected expression levels of a few genes involved in the GA biosynthesis and signaling pathways, as well as accumulation levels of bioactive GAs GA1 and GA3. Application of GA3 restored the accelerated petal senescence to normal levels in PhOBF1-RNAi transgenic petunia lines, and reduced ethylene release and transcription of three ethylene biosynthetic genes PhACO1, PhACS1, and PhACS2. Moreover, PhOBF1 was observed to specifically bind to the PhGA20ox3 promoter containing a G-box motif. Transient silencing of PhGA20ox3 in petunia plants through tobacco rattle virus-based virus-induced gene silencing method led to accelerated corolla senescence. Our results suggest that PhOBF1 functions as a negative regulator of ethylene-mediated flower senescence by modulating the GA production.

Genome-wide identification and expression analysis of the HD2 protein family and its response to drought and salt stress in Gossypium species

Histone deacetylase 2 (HD2) proteins play an important role in the regulation of gene expression. This helps with the growth and development of plants and also plays a crucial role in responses to biotic and abiotic stress es. HD2s comprise a C₂H₂-type Zn²⁺ finger at their C-terminal and an HD2 label, deacetylation and phosphorylation sites, and NLS motifs at their N-terminal. In this study, a total of 27 HD2 members were identified, using Hidden Markov model profiles, in two diploid cotton genomes (Gossypium raimondii and Gossypium arboretum) and two tetraploid cotton genomes (Gossypium hirsutum and Gossypium barbadense). These cotton HD2 members were classified into 10 major phylogenetic groups (I-X), of which group III was found to be the largest with 13 cotton HD2 members. An evolutionary investigation showed that the expansion of HD2 members primarily occurred as a result of segmental duplication in paralogous gene pairs. Further qRT-PCR validation of nine putative genes using RNA-Seq data suggested that GhHDT3D.2 exhibits significantly higher levels of expression at 12h, 24h, 48h, and 72h of exposure to both drought and salt stress conditions compared to a control measure at 0h. Furthermore, gene ontology, pathways, and co-expression network study of GhHDT3D.2 gene affirmed their significance in drought and salt stress responses.

The difference of the cell wall metabolism between ‘Fuyan’ and ‘Dongbi’ longans and its relationship with the pulp breakdown

The aims of present works were to explore the difference in pulp breakdown of 'Fuyan' and 'Dongbi' longans and its relationship with cell wall metabolism. Comparison with 'Fuyan' longan fruit, postharvest 'Dongbi' longan fruit showed lower pulp breakdown index, lower activities of PE, PG, cellulase, β-Gal, XET, and lower expression levels of their corresponding genes. In addition, higher levels of cell wall polysaccharides including ISP, CSP, cellulose and hemicellulose were exhibited in 'Dongbi' longan pulp. These findings implied that, the reduced activities of enzymes and the down-regulated expressions of genes-involved in cell wall disassembly were shown in 'Dongbi' longan pulp, which might reduce the dissolution of polysaccharides and maintain a higher structural integrity in 'Dongbi' longan pulp cell wall, and consequently the mitigated pulp breakdown was displayed in 'Dongbi' longan during storage.

Plant-specific HDT family histone deacetylases are nucleoplasmins

Histone acetyltransferase (HAT)- and histone deacetylase (HDAC)-mediated histone acetylation and deacetylation regulate nucleosome dynamics and gene expression. HDACs are classified into different families, with HD-tuins or HDTs being specific to plants. HDTs show some sequence similarity to nucleoplasmins, the histone chaperones that aid in binding, storing, and loading H2A/H2B dimers to assemble nucleosomes. Here, we solved the crystal structure of the N-terminal domain (NTD) of all four HDTs (HDT1, HDT2, HDT3, and HDT4) from Arabidopsis (Arabidopsis thaliana). The NTDs form a nucleoplasmin fold, exist as pentamers in solution, and are resistant to protease treatment, high temperature, salt, and urea conditions. Structurally, HDTs do not form a decamer, unlike certain classical nucleoplasmins. The HDT-NTD requires an additional A2 acidic tract C-terminal to the nucleoplasmin domain for interaction with histone H3/H4 and H2A/H2B oligomers. We also report the in-solution structures of HDT2 pentamers in complex with histone oligomers. Our study provides a detailed structural and in vitro functional characterization of HDTs, revealing them to be nucleoplasmin family histone chaperones. The experimental confirmation that HDTs are nucleoplasmins may spark new interest in this enigmatic family of proteins.

HD2A and HD2C co-regulate drought stress response by modulating stomatal closure and root growth in Arabidopsis

Histone deacetylase 2 (HD2) is a unique family of histone deacetylases (HDACs) in plants. Despite evidence that certain HD2 family HDACs play an important role in plant growth and stress response, the coordination of HD2s in these processes remains largely unknown. We found that HD2-type, HD2A and HD2C coordinate to play a role in drought stress response in Arabidopsis. We showed that the hd2a.hd2c double mutant (Mac16) exhibit decreased drought survival and increased water loss as compared to the single mutants, hd2a and hd2c. Gene expression analysis showed that the ABI1 and ABI2 genes were upregulated and SLAC1 was downregulated which led to the modified stomatal functioning in the Mac16 as compared to the single mutants. Overexpression of HD2A and HD2C showed enhanced drought survival and decreased water loss. We also showed that the GA2ox1 and GA2ox2 genes, which are involved in the catabolism of bioactive gibberellic acids, were upregulated in the Mac16 as compared to the single mutants, which led to a decreased root growth in the Mac16. Furthermore, we showed that HD2A and HD2C can physically interact and increased genome-wide H3K9 acetylation was observed in the Mac16, compared to the single mutants. Overall, our investigation revealed that HD2A and HD2C coordinate to play a cumulative role in drought stress response and root growth in Arabidopsis.

Short-Term Gaseous Treatments Improve Rachis Browning in Red and White Table Grapes Stored at Low Temperature: Molecular Mechanisms Underlying Its Beneficial Effect

Short-term gaseous treatments improve rachis quality during table grape postharvest, but little is known about the mechanisms involved. In this work, we observed that the application of a 3-day CO2 treatment at 0 °C improved rachis browning of Superior Seedless and Red Globe bunches, affecting the non-enzymatic antioxidant system by reducing the total phenolic content, the antioxidant activity and the expression of different stilbene synthase genes. Lipid peroxidation levels revealed lower oxidative stress in CO2-treated rachis of both cultivars linked to the activation of the enzymatic antioxidant system. Furthermore, whereas a positive correlation was denoted between rachis browning and the accumulation of key ABA regulatory genes in Red Globe bunches, this effect was restricted to ACS1, a key synthetic ethylene gene, in Superior Seedless clusters. This work also corroborated the important role of ethylene-responsive factors in the beneficial effect of the gaseous treatment, not only in the berries but also in the rachis. Finally, the application of the gaseous treatment avoided the induction of cell wall-degrading enzyme-related genes in both cultivars, which could favor the maintenance of rachis quality. This work provides new insight into specific responses modulated by the gaseous treatment focused on mitigating rachis browning independently of the cultivar.

Molecular and Genetic Events Determining the Softening of Fleshy Fruits: A Comprehensive Review

Fruit softening that occurs during fruit ripening and postharvest storage determines the fruit quality, shelf life and commercial value and makes fruits more attractive for seed dispersal. In addition, over-softening results in fruit eventual decay, render fruit susceptible to invasion by opportunistic pathogens. Many studies have been conducted to reveal how fruit softens and how to control softening. However, softening is a complex and delicate life process, including physiological, biochemical and metabolic changes, which are closely related to each other and are affected by environmental conditions such as temperature, humidity and light. In this review, the current knowledge regarding fruit softening mechanisms is summarized from cell wall metabolism (cell wall structure changes and cell-wall-degrading enzymes), plant hormones (ETH, ABA, IAA and BR et al.), transcription factors (MADS-Box, AP2/ERF, NAC, MYB and BZR) and epigenetics (DNA methylation, histone demethylation and histone acetylation) and a diagram of the regulatory relationship between these factors is provided. It will provide reference for the cultivation of anti-softening fruits.

Genome-Wide Analysis of the ERF Family and Identification of Potential Genes Involved in Fruit Ripening in Octoploid Strawberry

Ethylene response factors (ERFs) belonging to the APETALA2/ERF superfamily acted at the end of the ethylene signaling pathway, and they were found to play important roles in plant growth and development. However, the information of ERF genes in strawberry and their involvement in fruit ripening have been limited. Here, a total of 235 ERF members were identified from 426 AP2/ERF genes at octoploid strawberry genome level and classified into six subgroups according to their sequence characteristics and phylogenetic relationship. Conserved motif and gene structure analysis supported the evolutionary conservation of FaERFs. Syntenic analysis showed that four types of duplication events occurred during the expansion of FaERF gene family. Of these, WGD/segmental duplication played a major role. Transcriptomic data of FaERF genes during fruit ripening and in response to abscisic acid screened one activator (FaERF316) and one repressor (FaERF118) that were involved in fruit ripening. Transcriptional regulation analysis showed some transcription factors related to ripening such as ABI4, TCP15, and GLK1 could bind to FaERF316 or FaERF118 promoters, while protein-protein interaction analysis displayed some proteins associated with plant growth and development could interact with FaERF118 or FaERF316. These results suggested that FaERF118 and FaERF316 were potential genes to regulate strawberry ripening. In summary, the present study provides the comprehensive and systematic information on FaERF family evolution and gains insights into FaERF's potential regulatory mechanism in strawberry ripening.

Comprehensive Genome-Wide Analysis of Histone Acetylation Genes in Roses and Expression Analyses in Response to Heat Stress

Roses have high economic values as garden plants and for cut-flower and cosmetics industries. The growth and development of rose plants is affected by exposure to high temperature. Histone acetylation plays an important role in plant development and responses to various stresses. It is a dynamic and reversible process mediated by histone deacetylases (HDAC) and histone acetyltransferases (HAT). However, information on HDAC and HAT genes of roses is scarce. Here, 23 HDAC genes and 10 HAT genes were identified in the Rosa chinensis ‘Old Blush’ genome. Their gene structures, conserved motifs, physicochemical properties, phylogeny, and synteny were assessed. Analyses of the expression of HDAC and HAT genes using available RNAseq data showed that these genes exhibit different expression patterns in different organs of the three analyzed rose cultivars. After heat stress, while the expression of most HDAC genes tend to be down-regulated, that of HAT genes was up-regulated when rose plants were grown at high-temperature conditions. These data suggest that rose likely respond to high-temperature exposure via modification in histone acetylation, and, thus, paves the way to more studies in order to elucidate in roses the molecular mechanisms underlying rose plants development and flowering.

MdMADS6 Recruits Histone Deacetylase MdHDA19 to Repress the Expression of the Carotenoid Synthesis-Related Gene MdCCD1 during Fruit Ripening

Fruit ripening is regulated by epigenetic modifications and transcription factors, which may function independently or as protein complexes. Our previous study showed that the apple histone deacetylase19 (MdHDA19) suppresses fruit ripening through the deacetylation of histones in related genes. Here, a MADS-box transcription factor (MdMADS6) was identified using a yeast two-hybrid (Y2H) assay as a candidate protein that interacts with MdHDA19 during apple fruit ripening. Furthermore, Y2H, bimolecular fluorescence complementation (BiFC) and pull-down assays were used to confirm the interaction between MdHDA19 and MdMADS6. Agrobacterium-mediated transient transformation and yeast one-hybrid assays showed that MdMADS6 promoted carotenoid accumulation in apple fruit by acting on the downstream target genes related to carotenoid biosynthesis. In summary, we conclude that, in the early stages of fruit development, the expression of MdMADS6 was maintained at lower levels, where it interacted with MdHDA19 to form a protein complex that inhibited the expression of the downstream genes. At the late stages of fruit development, active expression of MdMADS6 dissociated the protein complex of MdMADS6 and MdHDA19 and consequently promoted the expression of carotenoid biosynthesis genes as well as carotenoid accumulation.

Epigenetic Mechanisms of Senescence in Plants

Senescence is a major developmental transition in plants that requires a massive reprogramming of gene expression and includes various layers of regulations. Senescence is either an age-dependent or a stress-induced process, and is under the control of complex regulatory networks that interact with each other. It has been shown that besides genetic reprogramming, which is an important aspect of plant senescence, transcription factors and higher-level mechanisms, such as epigenetic and small RNA-mediated regulators, are also key factors of senescence-related genes. Epigenetic mechanisms are an important layer of this multilevel regulatory system that change the activity of transcription factors (TFs) and play an important role in modulating the expression of senescence-related gene. They include chromatin remodeling, DNA methylation, histone modification, and the RNA-mediated control of transcription factors and genes. This review provides an overview of the known epigenetic regulation of plant senescence, which has mostly been studied in the form of leaf senescence, and it also covers what has been reported about whole-plant senescence.

Characterization of histone deacetylases and their roles in response to abiotic and PAMPs stresses in Sorghum bicolor

BACKGROUND

Histone deacetylases (HDACs) play an important role in the regulation of gene expression, which is indispensable in plant growth, development, and responses to environmental stresses. In Arabidopsis and rice, the molecular functions of HDACs have been well-described. However, systematic analysis of the HDAC gene family and gene expression in response to biotic and abiotic stresses has not been reported for sorghum.

RESULTS

We conducted a systematic analysis of the sorghum HDAC gene family and identified 19 SbHDACs mainly distributed on eight chromosomes. Phylogenetic tree analysis of SbHDACs showed that the gene family was divided into three subfamilies: RPD3/HDA1, SIR2, and HD2. Tissue-specific expression results showed that SbHDACs displayed different expression patterns in different tissues, indicating that these genes may perform different functions in growth and development. The expression pattern of SbHDACs under different stresses (high and low temperature, drought, osmotic and salt) and pathogen-associated molecular model (PAMPs) elf18, chitin, and flg22) indicated that SbHDAC genes may participate in adversity responses and biological stress defenses. Overexpression of SbHDA1, SbHDA3, SbHDT2 and SbSRT2 in Escherichia coli promoted the growth of recombinant cells under abiotic stress. Interestingly, we also showed that the sorghum acetylation level was enhanced when plants were under cold, heat, drought, osmotic and salt stresses. The findings will help us to understand the HDAC gene family in sorghum, and illuminate the molecular mechanism of the responses to abiotic and biotic stresses.

CONCLUSION

We have identified and classified 19 HDAC genes in sorghum. Our data provides insights into the evolution of the HDAC gene family and further support the hypothesis that these genes are important for the plant responses to abiotic and biotic stresses.

Histone deacetylase SbHDT701 in Sorghum bicolor reveals functions in response to stress factors by enhancing acetylation

Histone acetylation plays important roles in eukaryotic chromatin modification and gene expression regulation. Acetylation levels are modulated by histone deacetylases (HDACs), which function as key epigenetic factors that regulate gene expression in response to various stresses. HDT701, a member of the HD2 subfamily of HDACs, plays crucial roles in plant responses to abiotic stress and pathogen infection. Here, we analysed the expression pattern of SbHDT701 in sorghum. Real-time fluorescence quantitative PCR (RT-qPCR) results showed that expression of SbHDT701 was tissue-specific, and up-regulated under drought (d-mannitol) and salt (NaCl) stresses. We also determined the optimal expression conditions for SbHDT701 protein accumulation, and successfully expressed and purified SbHDT701 protein. Besides, overexpression of SbHDT701 in could promote the growth of recombinant cells under abiotic stress. SbHDT701 expression in Escherichia coli also increased acetylation modification levels following treatment with 750 mM NaCl, and 100 mM or 300 mM d-mannitol. In summary, the sorghum HDAC SbHDT701 mediates stress responses by enhancing acetylation modification levels.

HD2-type histone deacetylases: unique regulators of plant development and stress responses

Plants have developed sophisticated and complex epigenetic regulation-based mechanisms to maintain stable growth and development under diverse environmental conditions. Histone deacetylases (HDACs) are important epigenetic regulators in eukaryotes that are involved in the deacetylation of lysine residues of histone H3 and H4 proteins. Plants have developed a unique HDAC family, HD2, in addition to the RPD3 and Sir2 families, which are also present in other eukaryotes. HD2s are well conserved plant-specific HDACs, which were first identified as nucleolar phosphoproteins in maize. The HD2 family plays important roles not only in fundamental developmental processes, including seed germination, root and leaf development, floral transition, and seed development but also in regulating plant responses to biotic and abiotic stresses. Some of the HD2 members coordinate with each other to function. The HD2 family proteins also show functional association with RPD3-type HDACs and other transcription factors as a part of repression complexes in gene regulatory networks involved in environmental stress responses. This review aims to analyse and summarise recent research progress in the HD2 family, and to describe their role in plant growth and development and in response to different environmental stresses.

Transcriptome-wide identification and expression profiling of the ERF gene family suggest roles as transcriptional activators and repressors of fruit ripening in durian

The involvement of the phytohormone ethylene as the main trigger of climacteric fruit ripening is well documented. However, our knowledge regarding the role of ethylene response factor (ERF) transcription factor in the transcriptional regulation of ethylene biosynthesis during fruit ripening remains limited. Here, comprehensive transcriptome analysis and expression profiling revealed 63 ERFs in durian pulps, termed DzERF1-DzERF63, of which 34 exhibited ripening-associated expression patterns at three stages (unripe, midripe, and ripe) during fruit ripening. Hierarchical clustering analysis classified 34 ripening-associated DzERFs into three distinct clades, among which, clade I consisted of downregulated DzERFs and clade III included those upregulated during ripening. Phylogenetic analysis predicted the functions of some DzERFs based on orthologs of previously characterized ERFs. Among downregulated DzERFs, DzERF6 functional prediction revealed its role as a negative regulator of ripening via ethylene biosynthetic gene repression, whereas among upregulated genes, DzERF9 was predicted to positively regulate ethylene biosynthesis. Correlation network analysis of 34 ripening-associated DzERFs with potential target genes revealed a strong negative correlation between DzERF6 and ethylene biosynthetic genes and a strong positive correlation between DzERF9 and ethylene biosynthesis. DzERF6 and DzERF9 showed differential expression patterns in association with different ripening treatments (natural, ethylene-induced, and 1-methylcyclopropene-delayed ripening). DzERF6 was downregulated, whereas DzERF9 was upregulated, during ripening and after ethylene treatment. The auxin-repressed and auxin-induced expression of DzERF6 and DzERF9, respectively, confirmed its dose-dependent responsiveness to exogenous auxin. We suggest ethylene- and auxin-mediated roles of DzERF6 and DzERF9 during fruit ripening, possibly through transcriptional regulation of ethylene biosynthetic genes.

Multiomics analyses unveil the involvement of microRNAs in pear fruit senescence under high- or low-temperature conditions

Senescence leads to declines in fruit quality and shortening of shelf life. It is known that low temperatures (LTs) efficiently delay fruit senescence and that high temperatures (HTs) accelerate senescence. However, the molecular mechanism by which temperature affects senescence is unclear. Herein, through multiomics analyses of fruits subjected to postharvest HT, LT, and room temperature treatments, a total of 56 metabolic compounds and 700 mRNAs were identified to be associated with fruit senescence under HT or LT conditions. These compounds could be divided into antisenescent (I→III) and prosenescent (IV→VI) types. HT affected the expression of 202 mRNAs to enhance the biosynthesis of prosenescent compounds of types V and VI and to inhibit the accumulation of antisenescent compounds of types II and III. LT affected the expression of 530 mRNAs to promote the accumulation of antisenescent compounds of types I and II and to impede the biosynthesis of prosenescent compounds of types IV and V. Moreover, 16 microRNAs were isolated in response to HT or LT conditions and interacted with the mRNAs associated with fruit senescence under HT or LT conditions. Transient transformation of pear fruit showed that one of these microRNAs, Novel_188, can mediate fruit senescence by interacting with its target Pbr027651.1. Thus, both HT and LT conditions can affect fruit senescence by affecting microRNA-mRNA interactions, but the molecular networks are different in pear fruit.

Genome-wide identification of the HDAC family proteins and functional characterization of CsHD2C, a HD2-type histone deacetylase gene in tea plant (Camellia sinensis L. O. Kuntze)

The histone deacetylases (HDACs) are involved in growth, development and stress responses in many plants. However, the functions of HDACs in tea plant (Camellia sinensis L. O. Kuntze) and other woody plants remain unclear. Here, 18 CsHDAC genes were identified by genome-wide analysis in tea plant. The phylogenetic analysis demonstrated that the CsHDAC proteins were divided into three subfamilies, namely, the RPD3/HDA1 subfamily (8 members), the SIR2 subfamily (4 members) and the plant specific HD2 subfamily (6 members). The expression patterns showed that most members of CsHDACs family were regulated by different abiotic stress. High correlation was found between the expression of the CsHDACs and the accumulation of theanine, catechin, EGCG and other metabolites in tea plant. Most of the CsHDAC proteins were negative regulators. We further studied a specific gene CsHD2C (NCBI-ID: KY364373) in tea plant, which is the homolog of AtHD2C, encoded a protein of 306 aa. CsHD2C was highly expressed in leaves, young buds and stems. The transcription of CsHD2C was inhibited by ABA, NaCl and low temperature. It was found localized in the nucleus when fused with a YFP reporter gene. Overexpression of CsHD2C can rescue the phenotype related to different abiotic stresses in the mutant of AtHD2C in Arabidopsis. The stress-responsive genes RD29A, RD29B, ABI1 and ABI2 were also investigated to understand the regulating role of CsHD2C under abiotic stresses. We also found that CsHD2C could renew the change of acetylation level for histone H4 and the RNAP-II occupancy accumulation in the promoter of abiotic stress responses gene in the hd2c Arabidopsis mutant. Together, our results suggested that CsHD2C may act as a positive regulator in abiotic stress responses in tea plant.

Revealing Further Insights on Chilling Injury of Postharvest Bananas by Untargeted Lipidomics

Chilling injury is especially prominent in postharvest bananas stored at low temperature below 13 °C. To elucidate better the relationship between cell membrane lipids and chilling injury, an untargeted lipidomics approach using ultra-performance liquid chromatography-mass spectrometry was conducted. Banana fruit were stored at 6 °C for 0 (control) and 4 days and then sampled for lipid analysis. After 4 days of storage, banana peel exhibited a marked chilling injury symptom. Furthermore, 45 lipid compounds, including glycerophospholipids, saccharolipids, and glycerolipids, were identified with significant changes in peel tissues of bananas stored for 4 days compared with the control fruit. In addition, higher ratio of digalactosyldiacylglycerol (DGDG) to monogalactosyldiacylglycerol (MGDG) and higher levels of phosphatidic acid (PA) and saturated fatty acids but lower levels of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and unsaturated fatty acids were observed in banana fruit with chilling injury in contrast to the control fruit. Meanwhile, higher activities of phospholipase D (PLD) and lipoxygenase (LOX) were associated with significantly upregulated gene expressions of MaPLD1 and MaLOX2 and higher malondialdehyde (MDA) content in chilling injury-related bananas. In conclusion, our study indicated that membrane lipid degradation resulted from reduced PC and PE, but accumulated PA, while membrane lipid peroxidation resulted from the elevated saturation of fatty acids, resulting in membrane damage which subsequently accelerated the chilling injury occurrence of banana fruit during storage at low temperature.

Redox Components: Key Regulators of Epigenetic Modifications in Plants

Epigenetic modifications including DNA methylation, histone modifications, and chromatin remodeling are crucial regulators of chromatin architecture and gene expression in plants. Their dynamics are significantly influenced by oxidants, such as reactive oxygen species (ROS) and nitric oxide (NO), and antioxidants, like pyridine nucleotides and glutathione in plants. These redox intermediates regulate the activities and expression of many enzymes involved in DNA methylation, histone methylation and acetylation, and chromatin remodeling, consequently controlling plant growth and development, and responses to diverse environmental stresses. In recent years, much progress has been made in understanding the functional mechanisms of epigenetic modifications and the roles of redox mediators in controlling gene expression in plants. However, the integrated view of the mechanisms for redox regulation of the epigenetic marks is limited. In this review, we summarize recent advances on the roles and mechanisms of redox components in regulating multiple epigenetic modifications, with a focus of the functions of ROS, NO, and multiple antioxidants in plants.

Overexpression of ThSAP30BP from Tamarix hispida improves salt tolerance

Histone deacetylases (HDACs) play an important regulatory role in plant response to biotic and abiotic stresses. They improve plant stress resistance by increasing the degree of histone acetylation associated with stress-responsive genes. SAP30BP, a human transcriptional regulatory protein, can increase histone deacetylase activity by regulating the deacetylation levels of lysines 9 and 14 in histone H3. In this study, a ThSAP30BP gene was cloned and characterized from Tamarix hispida (a kind of woody halophyte). The expression patterns of ThSAP30BP under different abiotic stresses and hormone treatments were detected by qRT-PCR. The results showed that ThSAP30BP was significantly upregulated at most time points under various stress treatments, suggesting that ThSAP30BP may be related to the abiotic stress response of T. hispida. To further analyze the salt stress resistance function of the ThSAP30BP gene, the plant overexpression vector pROKII-ThSAP30BP was instantaneously constructed and transformed into T. hispida. Meanwhile, the empty vector pROKII was also transformed as a control. The activities of SOD and POD, the contents of H₂O₂ and MDA, the relative conductance and the staining of NBT, DAB and Evans blue were analyzed and compared under salt stress. The results showed that the overexpression of ThSAP30BP in T. hispida reduced the accumulation of ROS in plants and the cell death rate under salt stress. These results suggested that ThSAP30BP may play an important physiological role in salt tolerance of T. hispida.

Histone deacetylase gene PtHDT902 modifies adventitious root formation and negatively regulates salt stress tolerance in poplar

Histone deacetylases (HDACs) regulate gene transcription, and play a critical role in plant growth, development and stress responses. HD2 proteins are plant specific histone deacetylases. In woody plants, functions of HD2s are not known. In this study, we cloned an HD2 gene PtHDT902 from Populus trichocarpa and investigated its sequence, expression, subcellular localization, and functions in root development and salt stress responses. Our findings indicated that PtHDT902 was a nuclear protein and its expression was regulated by abiotic stresses. The over-expression of PtHDT902 in both Arabidopsis and poplar increased the expression levels of gibberellin (GA) biosynthetic genes. The expression of PtHDT902 in Arabidopsis enhanced primary root growth, and its over-expression in poplar inhibited adventitious root formation. These phenotypes resulted from over-expression of PtHDT902 were consistent with the GA-overproduction phenotypes. In addition, the poplar plants over-expressing PtHDT902 exhibited lower tolerance to salt than non-transgenic plants. These findings indicated that PtHDT902 worked as an important regulator in adventitious root formation and salt stress tolerance in poplar.

The expanding roles of APETALA2/Ethylene Responsive Factors and their potential applications in crop improvement

Understanding the molecular basis of the gene-regulatory networks underlying agronomic traits or plant responses to abiotic/biotic stresses is very important for crop improvement. In this context, transcription factors, which either singularly or in conjugation directly control the expression of many target genes, are suitable candidates for improving agronomic traits via genetic engineering. In this regard, members of one of the largest class of plant-specific APETALA2/Ethylene Response Factor (AP2/ERF) superfamily, which is implicated in various aspects of development and plant stress adaptation responses, are considered high-value targets for crop improvement. Besides their long-known regulatory roles in mediating plant responses to abiotic stresses such as drought and submergence, the novel roles of AP2/ERFs during fruit ripening or secondary metabolites production have also recently emerged. The astounding functional plasticity of AP2/ERF members is considered to be achieved by their interplay with other regulatory networks and signalling pathways. In this review, we have integrated the recently accumulated evidence from functional genomics studies and described their newly emerged functions in plants. The key structural features of AP2/ERF proteins and the modes of their action are briefly summarized. The importance of AP2/ERFs in plant development and stress responses and a summary of the event of their successful applications in crop improvement programs are also provided. Altogether, we envisage that the synthesized information presented in this review will be useful to design effective strategies for improving agronomic traits in crop plants.

Histone Deacetylase CpHDA3 Is Functionally Associated with CpERF9 in Suppression of CpPME1/2 and CpPG5 Genes during Papaya Fruit Ripening

Histone deacetylase (HDAC) performs important functions in plant growth and development, including fruit ripening. As a complex biological process, fruit ripening involves the histone acetylation modification of ripening-associated genes. Histone deacetylase genes (HDACs) have been well studied in Arabidopsis and rice, but the biological functions of HDACs in papaya are poorly understood. In the present work, three CpHDACs, belonging to the RPD3/HDA1 subfamily, were identified from papaya and named as CpHDA1, CpHDA2, and CpHDA3. CpHDA1 and CpHDA2 were induced by propylene, while CpHDA3 was propylene-repressed. Moreover, CpHDA3 protein could physically interact with CpERF9 and enhance the transcriptional repression activities of CpERF9 to downstream genes CpPME1, CpPME2 and CpPG5. Histone acetylation levels of CpPME1 and CpPG5 were increased during fruit ripening. Taken together, these results suggested that CpERF9 recruits CpHDA3 to form a histone deacetylase repressor complex to mediate pectin methylesterase and polygalacturonase genes expression during papaya fruit ripening and softening.

Fibroin Delays Chilling Injury of Postharvest Banana Fruit via Enhanced Antioxidant Capability during Cold Storage

storage Banana fruit after harvest is susceptible to chilling injury, which is featured by peel browning during cold, and it easily loses its nutrition and economic values. This study investigated the role of fibroin treatment in delaying peel browning in association with the antioxidant capability of postharvest banana fruit during cold storage. Compared to the control fruit, fibroin-treated fruit contained higher amounts of Pro and Cys during overall storage as well as higher glutathione (GSH) during the middle of storage. Conversely, fibroin-treated fruit exhibited a lower peel browning index and reactive oxygen species (ROS) level during overall storage as well as lower contents of hexadecanoic acid and octadecanoic acid by the end of storage compared to control fruit. In addition, fibroin-treated banana fruit showed higher activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) in relation to upregulation SOD, CAT, and GR as well as peroxiredoxins (MT3 and GRX) during the middle of storage. These results highlighted the role of fibroin treatment in reducing peel browning by enhancing the antioxidant capability of harvested banana fruit during cold storage.

Evolutionary diversification of type-2 HDAC structure, function and regulation in Nicotiana tabacum

Type-2 HDACs (HD2s) are plant-specific histone deacetylases that play diverse roles during development and in responses to biotic and abiotic stresses. In this study we characterized the six tobacco genes encoding HD2s that mainly differ by the presence or the absence of a typical zinc finger in their C-terminal part. Of particular interest, these HD2 genes exhibit a highly conserved intron/exon structure. We then further investigated the phylogenetic relationships among the HD2 gene family, and proposed a model of the genetic events that led to the organization of the HD2 family in Solanaceae. Absolute quantification of HD2 mRNAs in N. tabacum and in its precursors, N. tomentosiformis and N. sylvestris, did not reveal any pseudogenization of any of the HD2 genes, but rather specific regulation of HD2 expression in these three species. Functional complementation approaches in Arabidopsis thaliana demonstrated that the four zinc finger-containing HD2 proteins exhibit the same biological function in response to salt stress, whereas the two HD2 proteins without zinc finger have different biological function.

Integration of multi-omics techniques and physiological phenotyping within a holistic phenomics approach to study senescence in model and crop plants

The study of senescence in plants is complicated by diverse levels of temporal and spatial dynamics as well as the impact of external biotic and abiotic factors and crop plant management. Whereas the molecular mechanisms involved in developmentally regulated leaf senescence are very well understood, in particular in the annual model plant species Arabidopsis, senescence of other organs such as the flower, fruit, and root is much less studied as well as senescence in perennials such as trees. This review addresses the need for the integration of multi-omics techniques and physiological phenotyping into holistic phenomics approaches to dissect the complex phenomenon of senescence. That became feasible through major advances in the establishment of various, complementary 'omics' technologies. Such an interdisciplinary approach will also need to consider knowledge from the animal field, in particular in relation to novel regulators such as small, non-coding RNAs, epigenetic control and telomere length. Such a characterization of phenotypes via the acquisition of high-dimensional datasets within a systems biology approach will allow us to systematically characterize the various programmes governing senescence beyond leaf senescence in Arabidopsis and to elucidate the underlying molecular processes. Such a multi-omics approach is expected to also spur the application of results from model plants to agriculture and their verification for sustainable and environmentally friendly improvement of crop plant stress resilience and productivity and contribute to improvements based on postharvest physiology for the food industry and the benefit of its customers.

Transcriptome analysis during ripening of table grape berry cv. Thompson Seedless

Ripening is one of the key processes associated with the development of major organoleptic characteristics of the fruit. This process has been extensively characterized in climacteric fruit, in contrast with non-climacteric fruit such as grape, where the process is less understood. With the aim of studying changes in gene expression during ripening of non-climacteric fruit, an Illumina based RNA-Seq transcriptome analysis was performed on four developmental stages, between veraison and harvest, on table grapes berries cv Thompson Seedless. Functional analysis showed a transcriptional increase in genes related with degradation processes of chlorophyll, lipids, macromolecules recycling and nucleosomes organization; accompanied by a decrease in genes related with chloroplasts integrity and amino acid synthesis pathways. It was possible to identify several processes described during leaf senescence, particularly close to harvest. Before this point, the results suggest a high transcriptional activity associated with the regulation of gene expression, cytoskeletal organization and cell wall metabolism, which can be related to growth of berries and firmness loss characteristic to this stage of development. This high metabolic activity could be associated with an increase in the transcription of genes related with glycolysis and respiration, unexpected for a non-climacteric fruit ripening.

Cork Oak Young and Traumatic Periderms Show PCD Typical Chromatin Patterns but Different Chromatin-Modifying Genes Expression

Plants are subjected to adverse conditions being outer protective tissues fundamental to their survival. Tree stems are enveloped by a periderm made of cork cells, resulting from the activity of the meristem phellogen. DNA methylation and histone modifications have important roles in the regulation of plant cell differentiation. However, studies on its involvement in cork differentiation are scarce despite periderm importance. Cork oak periderm development was used as a model to study the formation and differentiation of secondary protective tissues, and their behavior after traumatic wounding (traumatic periderm). Nuclei structural changes, dynamics of DNA methylation, and posttranslational histone modifications were assessed in young and traumatic periderms, after cork harvesting. Lenticular phellogen producing atypical non-suberized cells that disaggregate and form pores was also studied, due to high impact for cork industrial uses. Immunolocalization of active and repressive marks, transcription analysis of the corresponding genes, and correlations between gene expression and cork porosity were investigated. During young periderm development, a reduction in nuclei area along with high levels of DNA methylation occurred throughout epidermis disruption. As cork cells became more differentiated, whole nuclei progressive chromatin condensation with accumulation in the nuclear periphery and increasing DNA methylation was observed. Lenticular cells nuclei were highly fragmented with faint 5-mC labeling. Phellogen nuclei were less methylated than in cork cells, and in lenticular phellogen were even lower. No significant differences were detected in H3K4me3 and H3K18ac signals between cork cells layers, although an increase in H3K4me3 signals was found from the phellogen to cork cells. Distinct gene expression patterns in young and traumatic periderms suggest that cork differentiation might be under specific silencing regulatory pathways. Significant correlations were found between QsMET1, QsMET2, and QsSUVH4 gene expression and cork porosity. This work evidences that DNA methylation and histone modifications play a role in cork differentiation and epidermis induced tension-stress. It also provides the first insights into chromatin dynamics during cork and lenticular cells differentiation pointing to a distinct type of remodeling associated with cell death.

Silencing of histone deacetylase SlHDT3 delays fruit ripening and suppresses carotenoid accumulation in tomato

The acetylation levels of histones on lysine residues are regulated by histone acetyltransferases and histone deacetylases, which play an important but understudied role in the control of gene expression in plants. There is an increasing research focus on histone deacetylation in crops, but to date, there is little information regarding tomato. With the aim of characterizing the tomato HD2 family of histone deacetylases, an RNA interference (RNAi) expression vector of SlHDT3 was constructed and transformed into tomato plants. The time of fruit ripening was delayed and the shelf life of the fruit was prolonged in SlHDT3 RNAi lines. The accumulation of carotenoid was decreased by altering of the carotenoid pathway flux. Ethylene content was also reduced and expression of ethylene biosynthetic genes (ACS2, ACS4 and ACO1, ACO3) and ripening-associated genes (RIN, E4, E8, PG, Pti4 and LOXB) was significantly down-regulated in SlHDT3 RNAi lines. The expression of genes involved in fruit cell wall metabolism (HEX, MAN, TBG4, XTH5 and XYL) was inhibited compared with wild type. These results indicate that SlHDT3 functions as a positive regulator of fruit ripening by affecting ethylene synthesis and carotenoid accumulation and that SlHDT3 lies upstream of SlMADS-RIN in the fruit ripening regulatory network.

Metabolomic and Proteomic Analysis of Maize Embryonic Callus induced from immature embryo

The low ratio of embryonic callus (EC) induction has inhibited the rapid development of maize genetic engineering. Still, little is known to explain the genotype-dependence of EC induction. Here, we performed a large-scale, quantitative analysis of the maize EC metabolome and proteome at three typical induction stages in two inbred lines with a range of EC induction capabilities. Comparison of the metabolomes and proteomes suggests that the differential molecular responses begin at an early stage of development and continue throughout the process of EC formation. The two inbred lines show different responses under various conditions, such as metal ion binding, cell enlargement, stem cell formation, meristematic activity maintenance, somatic embryogenesis, cell wall synthesis, and hormone signal transduction. Furthermore, the differences in hormone (auxin, cytokinin, gibberellin, salicylic acid, jasmonic acid, brassinosteroid and ethylene) synthesis and transduction ability could partially explain the higher EC induction ratio in the inbred line 18-599R. During EC formation, repression of the "histone deacetylase 2 and ERF transcription factors" complex in 18-599R activated the expression of downstream genes, which further promoted EC induction. Together, our data provide new insights into the molecular regulatory mechanism responsible for efficient EC induction in maize.

The transcriptional regulatory network mediated by banana (Musa acuminata) dehydration-responsive element binding (MaDREB) transcription factors in fruit ripening

Fruit ripening is a complex, genetically programmed process involving the action of critical transcription factors (TFs). Despite the established significance of dehydration-responsive element binding (DREB) TFs in plant abiotic stress responses, the involvement of DREBs in fruit ripening is yet to be determined. Here, we identified four genes encoding ripening-regulated DREB TFs in banana (Musa acuminata), MaDREB1, MaDREB2, MaDREB3, and MaDREB4, and demonstrated that they play regulatory roles in fruit ripening. We showed that MaDREB1-MaDREB4 are nucleus-localized, induced by ethylene and encompass transcriptional activation activities. We performed a genome-wide chromatin immunoprecipitation and high-throughput sequencing (ChIP-Seq) experiment for MaDREB2 and identified 697 genomic regions as potential targets of MaDREB2. MaDREB2 binds to hundreds of loci with diverse functions and its binding sites are distributed in the promoter regions proximal to the transcriptional start site (TSS). Most of the MaDREB2-binding targets contain the conserved (A/G)CC(G/C)AC motif and MaDREB2 appears to directly regulate the expression of a number of genes involved in fruit ripening. In combination with transcriptome profiling (RNA sequencing) data, our results indicate that MaDREB2 may serve as both transcriptional activator and repressor during banana fruit ripening. In conclusion, our study suggests a hierarchical regulatory model of fruit ripening in banana and that the MaDREB TFs may act as transcriptional regulators in the regulatory network.

Rosaceae Fruit Development, Ripening and Post-harvest: An Epigenetic Perspective

Rosaceae is a family with an extraordinary spectrum of fruit types, including fleshy peach, apple, and strawberry that provide unique contributions to a healthy diet for consumers, and represent an excellent model for studying fruit patterning and development. In recent years, many efforts have been made to unravel regulatory mechanism underlying the hormonal, transcriptomic, proteomic and metabolomic changes occurring during Rosaceae fruit development. More recently, several studies on fleshy (tomato) and dry (Arabidopsis) fruit model have contributed to a better understanding of epigenetic mechanisms underlying important heritable crop traits, such as ripening and stress response. In this context and summing up the results obtained so far, this review aims to collect the available information on epigenetic mechanisms that may provide an additional level in gene transcription regulation, thus influencing and driving the entire Rosaceae fruit developmental process. The whole body of information suggests that Rosaceae fruit could become also a model for studying the epigenetic basis of economically important phenotypes, allowing for their more efficient exploitation in plant breeding.

Papaya CpERF9 acts as a transcriptional repressor of cell-wall-modifying genes CpPME1/2 and CpPG5 involved in fruit ripening

KEY MESSAGE

CpERF9 controls papaya fruit ripening through transcriptional repression of cell-wall-modifying genes CpPME1/2 and CpPG5 by directly binding to their promoters. Papaya fruit ripening is an intricate and highly coordinated developmental process which is controlled by the action of ethylene and expression of numerous ethylene-responsive genes. Ethylene response factors (ERFs) representing the last regulators of ethylene-signaling pathway determine the specificities of ethylene response. However, knowledge concerning the transcriptional controlling mechanism of ERF-mediated papaya fruit ripening is limited. In the present work, a gene-encoding AP2/ERF protein with two ERF-associated amphiphilic repression (EAR) motifs, named CpERF9, was characterized from papaya fruit. CpERF9 was found to localize in nucleus, and possess transcriptional repression ability. CpERF9 expression steadily decreased during papaya fruit ripening, while several genes encoding pectin methylesterases (PMEs) and polygalacturonases (PGs), such as CpPME1/2 and CpPG5, were gradually increased, paralleling the decline of fruit firmness. Electrophoretic mobility shift assay (EMSA) demonstrated a specific binding of CpERF9 to promoters of CpPME1/2 and CpPG5, via the GCC-box motif. Transient expression of CpERF9 in tobacco repressed CpPME1/2 and CpPG5 promoter activities, which was depended on two EAR motifs of CpERF9 protein. Taken together, these findings suggest that papaya CpERF9 may act as a transcriptional repressor of several cell-wall modifying genes, such as CpPME1/2 and CpPG5, via directly binding to their promoters.

Banana Transcription Factor MaERF11 Recruits Histone Deacetylase MaHDA1 and Represses the Expression of MaACO1 and Expansins during Fruit Ripening

Phytohormone ethylene controls diverse developmental and physiological processes such as fruit ripening via modulation of ethylene signaling pathway. Our previous study identified that ETHYLENE RESPONSE FACTOR11 (MaERF11), a transcription factor in the ethylene signaling pathway, negatively regulates the ripening of banana, but the mechanism for the MaERF11-mediated transcriptional regulation remains largely unknown. Here we showed that MaERF11 has intrinsic transcriptional repression activity in planta. Electrophoretic mobility shift assay and chromatin immunoprecipitation analyses demonstrated that MaERF11 binds to promoters of three ripening-related Expansin genes, MaEXP2, MaEXP7 and MaEXP8, as well as an ethylene biosynthetic gene MaACO1, via the GCC-box motif. Furthermore, expression patterns of MaACO1, MaEXP2, MaEXP7, and MaEXP8 genes are correlated with the changes of histone H3 and H4 acetylation level during fruit ripening. Moreover, we found that MaERF11 physically interacts with a histone deacetylase, MaHDA1, which has histone deacetylase activity, and the interaction significantly strengthens the MaERF11-mediated transcriptional repression of MaACO1 and Expansins Taken together, these findings suggest that MaERF11 may recruit MaHDA1 to its target genes and repress their expression via histone deacetylation.

Proteomic Analysis of Differentially Expressed Proteins Involved in Peel Senescence in Harvested Mandarin Fruit

Mandarin (Citrus reticulata), a non-climacteric fruit, is an economically important fruit worldwide. The mechanism underlying senescence of non-climacteric fruit is poorly understood. In this study, a gel-based proteomic study followed by LC-ESI-MS/MS analysis was carried out to investigate the proteomic changes involved in peel senescence in harvested mandarin "Shatangju" fruit stored for 18 days. Over the course of the storage period, the fruit gradually senesced, accompanied by a decreased respiration rate and increased chlorophyll degradation and disruption of membrane integrity. Sixty-three proteins spots that showed significant differences in abundance were identified. The up-regulated proteins were mainly associated with cell wall degradation, lipid degradation, protein degradation, senescence-related transcription factors, and transcription-related proteins. In contrast, most proteins associated with ATP synthesis and scavenging of reactive oxygen species were significantly down-regulated during peel senescence. Three thioredoxin proteins and three Ca(2+) signaling-related proteins were significantly up-regulated during peel senescence. It is suggested that mandarin peel senescence is associated with energy supply efficiency, decreased antioxidant capability, and increased protein and lipid degradation. In addition, activation of Ca(2+) signaling and transcription factors might be involved in cell wall degradation and primary or secondary metabolism.

Genome-Wide Identification of the Transcription Factors Involved in Citrus Fruit Ripening from the Transcriptomes of a Late-Ripening Sweet Orange Mutant and Its Wild Type

Fruit ripening is a genetically programmed process. Transcription factors (TFs) play key roles in plant development and ripening by temporarily and spatially regulating the transcription of their target genes. In this study, a total of 159 TFs were identified from a spontaneous late-ripening mutant 'Fengwan' (C. sinensis L. Osbeck) sweet orange (MT) and its wild-type counterpart ('Fengjie 72–1', WT) along the ripening period via the Transcription Factor Prediction of PlantTFDB 3.0. Fifty-two differentially expressed TFs were identified between MT and WT; 92 and 120 differentially expressed TFs were identified in WT and MT, respectively. The Venn diagram analysis showed that 16 differentially expressed TFs were identified between MT and WT and during the ripening of WT and MT. These TFs were primarily assigned to the families of C2H2, Dof, bHLH, ERF, MYB, NAC and LBD. Particularly, the number of TFs of the ERF family was the greatest between MT and WT. According to the results of the WGCNA analysis, a weighted correlation network analysis tool, several important TFs correlated to abscisic acid (ABA), citric acid, fructose, glucose and sucrose were identified, such as RD26, NTT, GATA7 and MYB21/62/77. Hierarchical cluster analysis and the expression analysis conducted at five fruit ripening stages further validated the pivotal TFs that potentially function during orange fruit development and ripening.

Ethylene response factors in Arabidopsis immunity

Pathogen attack leads to transcriptional changes and metabolic modifications allowing the establishment of appropriate plant defences. Transcription factors (TFs) are key players in plant innate immunity. Notably, ethylene response factor (ERF) TFs are integrators of hormonal pathways and are directly responsible for the transcriptional regulation of several jasmonate (JA)/ethylene (ET)-responsive defence genes. Transcriptional activation or repression by ERFs is achieved through the binding to JA/ET-responsive gene promoters. In this review, we describe the regulation and mode of action at a molecular level of ERFs involved in Arabidopsis thaliana immunity. In particular, we focus on defence activators such as ERF1, ORA59, ERF6, and the recently described ERF96.

AtHD2D Gene Plays a Role in Plant Growth, Development, and Response to Abiotic Stresses in Arabidopsis thaliana

The histone deacetylases play important roles in the regulation of gene expression and the subsequent control of a number of important biological processes, including those involved in the response to environmental stress. A specific group of histone deacetylase genes, HD2, is present in plants. In Arabidopsis, HD2s include HD2A, HD2B, HD2C, and HD2D. Previous research showed that HD2A, HD2B, and HD2C are more related in terms of expression and function, but not HD2D. In this report, we studied different aspects of AtHD2D in Arabidopsis with respect to plant response to drought and other abiotic stresses. Bioinformatics analysis indicates that HD2D is distantly related to other HD2 genes. Transient expression in Nicotiana benthamiana and stable expression in Arabidopsis of AtHD2D fused with gfp showed that AtHD2D was expressed in the nucleus. Overexpression of AtHD2D resulted in developmental changes including fewer main roots, more lateral roots, and a higher root:shoot ratio. Seed germination and plant flowering time were delayed in transgenic plants expressing AtHD2D, but these plants exhibited higher degrees of tolerance to abiotic stresses, including drought, salt, and cold stresses. Physiological studies indicated that the malondialdehyde (MDA) content was high in wild-type plants but in plants overexpressing HD2D the MDA level increased slowly in response to stress conditions of drought, cold, and salt stress. Furthermore, electrolyte leakage in leaf cells of wild type plants increased but remained stable in transgenic plants. Our results indicate that AtHD2D is unique among HD2 genes and it plays a role in plant growth and development regulation and these changes can modulate plant stress responses.

EjAP2-1, an AP2/ERF gene, is a novel regulator of fruit lignification induced by chilling injury, via interaction with EjMYB transcription factors

Lignin biosynthesis is regulated by many transcription factors, such as those of the MYB and NAC families. However, the roles of AP2/ERF transcription factors in lignin biosynthesis have been rarely investigated. Eighteen EjAP2/ERF genes were isolated from loquat fruit (Eriobotrya japonica), which undergoes postharvest lignification during low temperature storage. Among these, expression of EjAP2-1, a transcriptional repressor, was negatively correlated with fruit lignification. The dual-luciferase assay indicated that EjAP2-1 could trans-repress activities of promoters of lignin biosynthesis genes from both Arabidopsis and loquat. However, EjAP2-1 did not interact with the target promoters (Ej4CL1). Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated protein-protein interactions between EjAP2-1 and lignin biosynthesis-related EjMYB1 and EjMYB2. Furthermore, repression effects on the Ej4CL1 promoter were observed with the combination of EjAP2-1 and EjMYB1 or EjMYB2, while EjAP2-1 with the EAR motif mutated (mEjAP2-1) lost such repression, although mEjAP2-1 still interacted with EjMYB protein. Based on these results, it is proposed that EjAP2-1 is an indirect transcriptional repressor on lignin biosynthesis, and the repression effects were manifested by EAR motifs and were conducted via protein-protein interaction with EjMYBs.

Application of α-aminoisobutyric acid and β-aminoisobutyric acid inhibits pericarp browning of harvested longan fruit

BACKGROUND

Pericarp browning is a critical problem resulting in reduced commercial value and shelf life of longan fruit.

RESULTS

Two non-protein amino acids, α-aminoisobutyric acid (AIB) and β-aminoisobutyric acid (BAIB) at 100 and 1 mM were applied to longan fruit prior to storage for up to 8 days at 25 °C respectively. Contents of the major five phenolics (gallic acid, catechin, corilagin, epicatechin and gallocatechin gallate) were assayed by high-performance liquid chromatography (HPLC). Physiological properties related to pericarp browning of longan fruit were investigated during storage. Respiration rate, membrane permeability, malondialdehyde (MDA) content, and activities of polyphenol oxidase (PPO) and peroxidase (POD) were down-regulated by AIB or BAIB treatments, with significantly lower pericarp browning index and higher proportion of edible fruit than the control. Moreover, exogenous application of AIB and BAIB maintained higher contents of catechin, corilagin, epicatechin and gallocatechin gallate, but lower content of gallic acid compared to the control in the pericarp of longan fruit during storage, which was associated with the oxidation of browning substrate.

CONCLUSIONS

Pericarp browning was inhibited and storage life of longan fruit was extended effectively by AIB and BAIB treatments with AIB treatment being more significant than BAIB. The findings may provide a new strategy for controlling pericarp browning of harvested longan fruit.

The Potato ERF Transcription Factor StERF3 Negatively Regulates Resistance to Phytophthora infestans and Salt Tolerance in Potato

Ethylene response factors (ERFs) are unique to the plant kingdom and play crucial roles in plant response to various biotic and abiotic stresses. We show here that a potato StERF3, which contains an ERF-associated amphiphilic repression (EAR) motif in its C-terminal region, negatively regulates resistance to Phytophthora infestans and salt tolerance in potato. The StERF3 promoter responds to induction by salicylic acid, ABA ethylene and NaCl, as well as P. infestans, the causal agent of potato late blight disease. StERF3 could bind to the GCC box element of the HIS3 promoter and activate transcription of HIS3 in yeast cells. Importantly, silencing of StERF3 in potato produced an enhanced foliage resistance to P. infestans and elevated plant tolerance to NaCl stress accompanied by the activation of defense-related genes (PR1, NPR1 and WRKY1). In contrast, StERF3-overexpressing plants showed reduced expression of these defense-related genes and enhanced susceptibility to P. infestans, suggesting that StERF3 functions as a negative regulator of downstream defense- and/or stress-related genes in potato. StERF3 is localized to the nucleus. Interestingly, yeast two-hybrid assay and a bimolecular fluorescence complementation (BiFC) test clarified that StERF3 could interact with other proteins in the cytoplasm which may lead to its re-localization between the nucleus and cytoplasm, revealing a novel means of StERF3 regulation. Taken together, these data provide new insights into the mechanism underlying how StERF3 negatively regulates late blight resistance and abiotic tolerance in potato and may have a potential use in engineering late blight resistance in potato.

Type-II histone deacetylases: elusive plant nuclear signal transducers

Since the beginning of the 21st century, numerous studies have concluded that the plant cell nucleus is one of the cellular compartments that define the specificity of the cellular response to an external stimulus or to a specific developmental stage. To that purpose, the nucleus contains all the enzymatic machinery required to carry out a wide variety of nuclear protein post-translational modifications (PTMs), which play an important role in signal transduction pathways leading to the modulation of specific sets of genes. PTMs include protein (de)acetylation which is controlled by the antagonistic activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Regarding protein deacetylation, plants are of particular interest: in addition to the RPD3-HDA1 and Sir2 HDAC families that they share with other eukaryotic organisms, plants have developed a specific family called type-II HDACs (HD2s). Interestingly, these HD2s are well conserved in plants and control fundamental biological processes such as seed germination, flowering or the response to pathogens. The aim of this review was to summarize current knowledge regarding this fascinating, but still poorly understood nuclear protein family.