p-Azaquinodimethane: A Versatile Quinoidal Moiety for Functional Materials Discovery.

ConspectusThe past 50 years of discovery in organic electronics have been driven in large part by the donor-acceptor design principle, wherein electron-rich and electron-poor units are assembled in conjugation with each other to produce small band gap materials. While the utility of this design strategy is undoubtable, it has been largely exhausted as a frontier of new avenues to produce and tune novel functional materials to meet the needs of the ever-increasing world of organic electronics applications. Its sister strategy of joining quinoidal and aromatic groups in conjugation has, by comparison, received much less attention, to a great extent due to the categorically poor stability of quinoidal conjugated motifs.In 2017 though, the p-azaquinodimethane (AQM) motif was first unveiled, which showed a remarkable level of stability despite being a close structural analogue to p-quinodimethane, a notably reactive compound. In contrast, dialkoxy AQM small molecules and polymers are stable even under harsh conditions and could thus be incorporated into conjugated polymers. When polymerized with aromatic subunits, these AQM-based polymers show notably reduced band gaps that follow reversed structure-property trends to some of their donor-acceptor polymer counterparts and yield organic field-effect transistor (OFET) hole mobilities above 5 cm2 V-1 s-1. Additionally, in an ongoing study, these AQM-based compounds are also showing promise as singlet fission (SF) active materials due to their mild diradicaloid character.An expanded world of AQMs was accessed through their ditriflate derivatives, which were first used to produce ionic AQMs (iAQMs) sporting two directly attached cationic groups that significantly affect the AQM motif's electronics, producing strongly electron-withdrawing quinoidal building blocks. Conjugated polyelectrolytes (CPEs) created with these iAQM building blocks exhibit optical band gaps stretching into the near-infrared I (NIR-I) region and showed exemplary behavior as photothermal therapy agents.In contrast to these stable AQM examples, the synthetic exploration of AQMs also produced examples of more typical diradicaloid reactivity but in forms that were controllable and produced intriguing and high-value products. With certain substitution patterns, AQMs were found to dimerize to form highly substituted [2.2]paracyclophanes in distinctly more appreciable yields than typical cyclophane formation reactions. Certain AQM ditriflates, when crystallized, undergo light-induced topochemical polymerization to form ultrahigh molecular weight (>106 Da) polymers that showed excellent performances as dielectric energy storage materials. These same AQM ditriflates could be used to produce the strongly electron-donating redox-active pentacyclic structure: pyrazino[2,3-b:5,6-b']diindolizine (PDIz). The PDIz motif allowed for the synthesis of exceedingly small band gap (0.7 eV) polymers with absorbances reaching all the way into the NIR-II region that were also found to produce strong photothermal effects. Both as stable quinoidal building blocks and through their controllable diradicaloid reactivity, AQMs have already proven to be versatile and effective as functional organic electronics materials.

MaMYB4 is a negative regulator and a substrate of RING-type E3 ligases MaBRG2/3 in controlling banana fruit ripening.

Fruit ripening is a complex developmental process, which is modulated by both transcriptional and post-translational events. Control of fruit ripening is important in maintaining moderate quality traits and minimizing postharvest deterioration. In this study, we discovered that the transcription factor MaMYB4 acts as a negative regulator of fruit ripening in banana. The protein levels of MaMYB4 decreased gradually with banana fruit ripening, paralleling ethylene production, and decline in firmness. DNA affinity purification sequencing combined with RNA-sequencing analyses showed that MaMYB4 preferentially binds to the promoters of various ripening-associated genes including ethylene biosynthetic and cell wall modifying genes. Furthermore, ectopic expression of MaMYB4 in tomato delayed tomato fruit ripening, which was accompanied by downregulation of ethylene biosynthetic and cell wall modifying genes. Importantly, two RING finger E3 ligases MaBRG2/3, whose protein accumulation increased progressively with fruit ripening, were found to interact with and ubiquitinate MaMYB4, contributing to decreased accumulation of MaMYB4 during fruit ripening. Transient overexpression of MaMYB4 and MaBRG2/3 in banana fruit ripening delayed or promoted fruit ripening by inhibiting or stimulating ethylene biosynthesis, respectively. Taken together, we demonstrate that MaMYB4 negatively modulates banana fruit ripening, and that MaMYB4 abundance could be regulated by protein ubiquitination, thus providing insights into the role of MaMYB4 in controlling fruit ripening at both transcriptional and post-translational levels.

Phosphorylation of transcription factor bZIP21 by MAP kinase MPK6-3 enhances banana fruit ripening.

Ripening of fleshy fruits involves both diverse post-translational modifications (PTMs) and dynamic transcriptional reprogramming, but the interconnection between PTMs, such as protein phosphorylation and transcriptional regulation, in fruit ripening remains to be deciphered. Here, we conducted a phosphoproteomic analysis during banana (Musa acuminata) ripening and identified 63 unique phosphopeptides corresponding to 49 proteins. Among them, a Musa acuminata basic leucine zipper transcription factor21 (MabZIP21) displayed elevated phosphorylation level in the ripening stage. MabZIP21 transcript and phosphorylation abundance increased during banana ripening. Genome-wide MabZIP21 DNA binding assays revealed MabZIP21-regulated functional genes contributing to banana ripening, and electrophoretic mobility shift assay, chromatin immunoprecipitation coupled with quantitative polymerase chain reaction, and dual-luciferase reporter analyses demonstrated that MabZIP21 stimulates the transcription of a subset of ripening-related genes via directly binding to their promoters. Moreover, MabZIP21 can be phosphorylated by MaMPK6-3, which plays a role in banana ripening, and T318 and S436 are important phosphorylation sites. Protein phosphorylation enhanced MabZIP21-mediated transcriptional activation ability, and transient overexpression of the phosphomimetic form of MabZIP21 accelerated banana fruit ripening. Additionally, MabZIP21 enlarges its role in transcriptional regulation by activating the transcription of both MaMPK6-3 and itself. Taken together, this study reveals an important machinery of protein phosphorylation in banana fruit ripening in which MabZIP21 is a component of the complex phosphorylation pathway linking the upstream signal mediated by MaMPK6-3 with transcriptional controlling of a subset of ripening-associated genes.

SlJMJ7 orchestrates tomato fruit ripening via crosstalk between H3K4me3 and DML2-mediated DNA demethylation.

The ripening of fleshy fruits is a unique developmental process that Arabidopsis and rice lack. This process is driven by hormones and transcription factors. However, the critical and early regulators of fruit ripening are still poorly understood. Here, we revealed that SlJMJ7, an H3K4 demethylase, is a critical negative regulator of fruit ripening in tomato. Combined genome-wide transcription, binding sites, histone H3K4me3 and DNA methylation analyses demonstrated that SlJMJ7 regulates a key group of ripening-related genes, including ethylene biosynthesis (ACS2, ACS4 and ACO6), transcriptional regulation (RIN and NOR) and DNA demethylation (DML2) genes, by H3K4me3 demethylation. Moreover, loss of SlJMJ7 function leads to increased H3K4me3 levels, which directly activates ripening-related genes, and to global DML2-mediated DNA hypomethylation in fruit, which indirectly prompts expression of ripening-related genes. Together, these effects lead to accelerated fruit ripening in sljmj7 mutant. Our findings demonstrate that SlJMJ7 acts as a master negative regulator of fruit ripening not only through direct removal of H3K4me3 from multiple key ripening-related factors, but also through crosstalk between histone and DNA demethylation. These findings reveal a novel crosstalk between histone methylation and DNA methylation to regulate gene expression in plant developmental processes.

SWI3B and HDA6 interact and are required for transposon silencing in Arabidopsis.

Although the interplay of covalent histone acetylation/deacetylation and ATP-dependent chromatin remodelling is crucial for the regulation of chromatin structure and gene expression in eukaryotes, the underlying molecular mechanism in plants remains largely unclear. Here we show a direct interaction between Arabidopsis SWI3B, an essential subunit of the SWI/SNF chromatin-remodelling complex, and the RPD3/HDA1-type histone deacetylase HDA6 both in vitro and in vivo. Furthermore, SWI3B and HDA6 co-repress the transcription of a subset of transposons. Both SWI3B and HDA6 maintain transposon silencing by decreasing histone H3 lysine 9 acetylation, but increasing histone H3 lysine 9 di-methylation, DNA methylation and nucleosome occupancy. Our findings reveal that SWI3B and HDA6 may act in the same co-repressor complex to maintain transposon silencing in Arabidopsis.

Rice histone deacetylase HDA704 positively regulates drought and salt tolerance by controlling stomatal aperture and density.

MAIN CONCLUSION: HDA704 enhances drought and salt tolerance via stomata-regulated mechanism. HDA704 negatively regulates stomatal aperture and density, repressing the transcription of DST and ABIL2 by histone deacetylation modification. Drought and salinity can damage crop growth and reduce yield. Stomata play an important role in abiotic stress tolerance. In this study on rice, we identified the RPD3/HDA1-type histone deacetylase HDA704 as a positive regulatory factor in drought and salt tolerance. HDA704 was induced by drought and salt stresses. Overexpression of HDA704 in transgenic rice promoted stomatal closure, decreased the number of stomata and slowed down the rate of water loss, consequently resulting in increased drought and salt tolerance. By contrast, knockdown of HDA704 in transgenic rice decreased stomatal closure and accelerated the rate of water loss, leading to decrease drought and salt tolerance. We detected the transcript expression of DST (Drought and Salt Tolerance) and ABIL2 (Abscisic Acid-insensitive Like2), which positively regulate stomatal aperture and density in rice. Our results showed that HDA704 directly binds to DST and ABIL2, repressing their expression via histone deacetylation modification. Collectively, these findings reveal that HDA704 positively regulates drought and salt tolerance by repressing the expression of DST and ABIL2. Our findings provide a new insight into the molecular mechanisms of stomata-regulated abiotic stress tolerance of plants.

Cystathionine beta-lyase is crucial for embryo patterning and the maintenance of root stem cell niche in Arabidopsis.

The growth and development of roots in plants depends on the specification and maintenance of the root apical meristem. Here, we report the identification of CBL, a gene required for embryo and root development in Arabidopsis, and encodes cystathionine beta-lyase (CBL), which catalyzes the penultimate step in methionine (Met) biosynthesis, and which also led to the discovery of a previous unknown, but crucial, metabolic contribution by the Met biosynthesis pathway. CBL is expressed in embryos and shows quiescent center (QC)-enriched expression pattern in the root. cbl mutant has impaired embryo patterning, defective root stem cell niche, stunted root growth, and reduces accumulation of the root master regulators PLETHORA1 (PLT1) and PLT2. Furthermore, mutation in CBL severely decreases abundance of several PIN-FORMED (PIN) proteins and impairs auxin-responsive gene expression in the root tip. cbl seedlings also exhibit global reduction in histone H3 Lys-4 trimethylation (H3K4me3) and DNA methylation. Importantly, mutation in CBL reduces the abundance of H3K4me3 modification in PLT1/2 genes and downregulates their expression. Overexpression of PLT2 partially rescues cbl root meristem defect, suggesting that CBL acts in part through PLT1/2. Moreover, exogenous supplementation of Met also restores the impaired QC activity and the root growth defects of cbl. Taken together, our results highlight the unique role of CBL to maintain the root stem cell niche by cooperative actions between Met biosynthesis and epigenetic modification of key developmental regulators.

Transcriptome sequencing and metabolite profiling analyses provide comprehensive insight into molecular mechanisms of flower development in Dendrobium officinale (Orchidaceae).

KEY MESSAGE: This research provides comprehensive insight into the molecular networks and molecular mechanisms underlying D. officinale flower development. Flowers are complex reproductive organs and play a crucial role in plant propagation, while also providing sustenance for insects and natural bioactive metabolites for humans. However, knowledge about gene regulation and floral metabolomes in flowers is limited. In this study, we used an important orchid species (Dendrobium officinale), whose flowers can be used to make herbal tea, to perform transcriptome sequencing and metabolic profiling of early- and medium-stage flower buds, as well as opened flowers, to provide comprehensive insight into the molecular mechanisms underlying flower development. A total of 8019 differentially expressed genes (DEGs) and 239 differentiated metabolites were found. The transcription factors that were identified and analyzed belong exclusively to the MIKC-type MADS-box proteins and auxin responsive factors that are known to be involved in flower development. The expression of genes involved in chlorophyll and carotenoid biosynthesis strongly matched the metabolite accumulation patterns. The genes related to flavonoid and polysaccharide biosynthesis were active during flower development. Interestingly, indole-3-acetic acid and abscisic acid, whose trend of accumulation was inverse during flower development, may play an important role in this process. Collectively, the identification of DEGs and differentiated metabolites could help to illustrate the regulatory networks and molecular mechanisms important for flower development in this orchid.

Singlet Fission in a para-Azaquinodimethane-Based Quinoidal Conjugated Polymer.

The exploitation of singlet fission (SF) in photovoltaic devices is restricted by the limited number of SF materials available and the conflicting requirement of intermolecular interactions to satisfy both efficient SF and subsequent triplet extraction. Intramolecular SF (iSF) represents an emerging alternative and may prove simpler to implement in devices. On account of the excellent chemical structure tunability and solution processability, conjugated polymers have emerged as promising candidates for iSF materials despite being largely underexplored. It remains a significant challenge to develop SF-capable conjugated polymers and achieve efficient dissociation of the formed triplet pairs simultaneously. In this contribution, we present a new iSF material in a para-azaquinodimethane-based quinoidal conjugated polymer. Using transient optical techniques, we show that an ultrafast iSF process dominates the deactivation of the excited state in such polymer, featuring ultrafast population (<1 ps) and stepwise dissociation of triplet pairs. Notably, these multiexciton states could further diffuse apart to produce long-lived free triplets (tens of µs) in strongly coupled aggregates in solid thin film. Such findings not only introduce a new iSF-active conjugated polymer to the rare SF material family but also shed unique insight into interchain interaction-promoted triplet pair dissociation in aggregates of conjugated polymers, thus openning new avenues for developing next-generation SF-based photovoltaic materials.

Histone demethylase SlJMJ6 promotes fruit ripening by removing H3K27 methylation of ripening-related genes in tomato.

Fruit ripening is governed by a complex regulatory network. Reversible histone methylation and demethylation regulate chromatin structure and gene expression. However, little is known about the involvement of histone demethylases in regulating fruit ripening. Here, we found that the tomato (Solanum lycopersicum) SlJMJ6 encodes a histone lysine demethylase that specifically demethylates H3K27 methylation. Overexpression of SlJMJ6 accelerates tomato fruit ripening, which is associated with the upregulated expression of a large number of ripening-related genes. Integrated analysis of RNA-seq and chromatin immunoprecipitation followed by sequencing identified 32 genes directly targeted by SlJMJ6 and transcriptionally upregulated with decreased H3K27m3 in SlJMJ6-overexpressed fruit. Numerous SlJMJ6-regulated genes are involved in transcription regulation, ethylene biosynthesis, cell wall degradation and hormone signaling. Eleven ripening-related genes including RIPENING INHIBITOR (RIN), 1-aminocyclopropane 1-carboxylate synthase-4 (ACS4), 1-aminocyclopropane-1-carboxylate oxidase 1 (ACO1), pectate lyase (PL) and beta-galactosidase 4 (TBG4), and a DNA demethylase DML2, were confirmed to be regulated directly by SlJMJ6 through removing H3K27me3. Our results demonstrate that SlJMJ6 is a ripening-prompting H3K27me3 demethylase that activates the expression of the ripening-related genes by modulating H3K27me3, thereby facilitating tomato fruit ripening. Our work also reveals a novel link between histone demethylation and DNA demethylation in regulating fruit ripening. To our knowledge, this is the first report of the involvement of a histone lysine demethylase in the regulation of fruit ripening.

HY5 Interacts with the Histone Deacetylase HDA15 to Repress Hypocotyl Cell Elongation in Photomorphogenesis.

Photomorphogenesis is a critical plant developmental process that involves light-mediated transcriptome and histone modification changes. The transcription factor ELONGATED HYPOCOTYL5 (HY5) acts downstream of multiple families of photoreceptors to promote photomorphogenesis by regulating the expression of light-responsive genes. However, the molecular mechanism for HY5-mediated transcriptional regulation remains largely unclear. Here, we demonstrated that HY5 directly interacts with a Reduced Potassium Dependence3/Histone Deacetylase1 (HDA1)-type histone deacetylase, HDA15, both in vitro and in vivo. Phenotypic analysis revealed that HDA15 is a negative regulator of hypocotyl cell elongation under both red and far-red light conditions in Arabidopsis (Arabidopsis thaliana) seedlings. The enzymatic activity of HDA15 is required for inhibition of hypocotyl elongation. Furthermore, HDA15 and HY5 act interdependently in the repression of hypocotyl cell elongation in photomorphogenesis. Genome-wide transcriptome analysis revealed that HDA15 and HY5 corepress the transcription of a subset of cell wall organization and auxin signaling-related genes. In addition, HDA15 is required for the function of HY5 in the repression of genes related to hypocotyl cell elongation in Arabidopsis seedlings. Moreover, HY5 recruits HDA15 to the promoters of target genes and represses gene expression by decreasing the levels of histone H4 acetylation in a light-dependent manner. Our study revealed a key transcription regulatory node in which HY5 interacts with HDA15 involved in repressing hypocotyl cell elongation to promote photomorphogenesis.

KNOX protein KNAT1 regulates fruitlet abscission in litchi by repressing ethylene biosynthetic genes.

Abscission is triggered by multiple environmental and developmental cues, including endogenous plant hormones. KNOTTED-LIKE HOMEOBOX (KNOX) transcription factors (TFs) play an important role in controlling abscission in plants. However, the underlying molecular mechanism of KNOX TFs in abscission is largely unknown. Here, we identified LcKNAT1, a KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1)-like protein from litchi, which regulates abscission by modulating ethylene biosynthesis. LcKNAT1 is expressed in the fruit abscission zone and its expression decreases during fruitlet abscission. Furthermore, the expression of the ethylene biosynthetic genes LcACS1, LcACS7, and LcACO2 increases in the fruit abscission zone, in parallel with the emission of ethylene in fruitlets. In vitro and in vivo assays revealed that LcKNAT1 inhibits the expression of LcACS/ACO genes by directly binding to their promoters. Moreover, ectopic expression of LcKNAT1 represses flower abscission in tomatoes. Transgenic plants expressing LcKNAT1 also showed consistently decreased expression of ACS/ACO genes. Collectively, these results indicate that LcKNAT1 represses abscission via the negative regulation of ethylene biosynthesis.

Identification of HDA15-PIF1 as a key repression module directing the transcriptional network of seed germination in the dark.

Light is a major external factor in regulating seed germination. Photoreceptor phytochrome B (PHYB) plays a predominant role in promoting seed germination in the initial phase after imbibition, partially by repressing phytochrome-interacting factor1 (PIF1). However, the mechanism underlying the PHYB-PIF1-mediated transcription regulation remains largely unclear. Here, we identified that histone deacetylase15 (HDA15) is a negative component of PHYB-dependent seed germination. Overexpression of HDA15 in Arabidopsis inhibits PHYB-dependent seed germination, whereas loss of function of HDA15 increases PHYB-dependent seed germination. Genetic evidence indicated that HDA15 acts downstream of PHYB and represses seed germination dependent on PIF1. Furthermore, HDA15 interacts with PIF1 both in vitro and in vivo. Genome-wide transcriptome analysis revealed that HDA15 and PIF1 co-regulate the transcription of the light-responsive genes involved in multiple hormonal signaling pathways and cellular processes in germinating seeds in the dark. In addition, PIF1 recruits HDA15 to the promoter regions of target genes and represses their expression by decreasing the histone H3 acetylation levels in the dark. Taken together, our analysis uncovered the role of histone deacetylation in the light-regulated seed germination process and identified that HDA15-PIF1 acts as a key repression module directing the transcription network of seed germination.

The Arabidopsis SWI2/SNF2 Chromatin Remodeling ATPase BRAHMA Targets Directly to PINs and Is Required for Root Stem Cell Niche Maintenance.

BRAHMA (BRM), a SWI/SNF chromatin remodeling ATPase, is essential for the transcriptional reprogramming associated with development and cell differentiation in Arabidopsis thaliana. In this study, we show that loss-of-function mutations in BRM led to defective maintenance of the root stem cell niche, decreased meristematic activity, and stunted root growth. Mutations of BRM affected auxin distribution by reducing local expression of several PIN-FORMED (PIN) genes in the stem cells and impaired the expression of the stem cell transcription factor genes PLETHORA (PLT1) and PLT2. Chromatin immunoprecipitation assays showed that BRM could directly target to the chromatin of PIN1, PIN2, PIN3, PIN4, and PIN7. In addition, genetic interaction assays indicate that PLTs acted downstream of BRM, and overexpression of PLT2 partially rescued the stem cell niche defect of brm mutants. Taken together, these results support the idea that BRM acts in the PLT pathway to maintain the root stem cell niche by altering the expression of PINs.

Arabidopsis BREVIPEDICELLUS interacts with the SWI2/SNF2 chromatin remodeling ATPase BRAHMA to regulate KNAT2 and KNAT6 expression in control of inflorescence architecture.

BREVIPEDICELLUS (BP or KNAT1), a class-I KNOTTED1-like homeobox (KNOX) transcription factor in Arabidopsis thaliana, contributes to shaping the normal inflorescence architecture through negatively regulating other two class-I KNOX genes, KNAT2 and KNAT6. However, the molecular mechanism of BP-mediated transcription regulation remains unclear. In this study, we showed that BP directly interacts with the SWI2/SNF2 chromatin remodeling ATPase BRAHMA (BRM) both in vitro and in vivo. Loss-of-function BRM mutants displayed inflorescence architecture defects, with clustered inflorescences, horizontally orientated pedicels, and short pedicels and internodes, a phenotype similar to the bp mutants. Furthermore, the transcript levels of KNAT2 and KNAT6 were elevated in brm-3, bp-9 and brm-3 bp-9 double mutants. Increased histone H3 lysine 4 tri-methylation (H3K4me3) levels were detected in brm-3, bp-9 and brm-3 bp-9 double mutants. Moreover, BRM and BP co-target to KNAT2 and KNAT6 genes, and BP is required for the binding of BRM to KNAT2 and KNAT6. Taken together, our results indicate that BP interacts with the chromatin remodeling factor BRM to regulate the expression of KNAT2 and KNAT6 in control of inflorescence architecture.

para-Azaquinodimethane: A Compact Quinodimethane Variant as an Ambient Stable Building Block for High-Performance Low Band Gap Polymers.

Quinoidal structures incorporating expanded para-quinodimethane (p-QM) units have garnered great interest as functional organic electronic, optical, and magnetic materials. The direct use of the compact p-QM unit as an electronic building block, however, has been inhibited by the high reactivity conveyed by its biradical character. Herein, we introduce a stable p-QM variant, namely p-azaquinodimethane (p-AQM), that incorporates nitrogen atoms in the central ring and alkoxy substituents on the periphery to increase the stability of the quinoidal structure. The succinct synthesis from readily available precursors leads to regio- and stereospecific p-AQMs that can be readily integrated into the backbone of conjugated polymers. The quinoidal character of the p-AQM unit endows the resulting polymers with narrow band gaps and high carrier transport mobilities. The study of a series of copolymers employing different numbers of thiophene units revealed an unconventional trend in band gaps, which is distinct from the widely adopted donor-acceptor approach to tuning the band gaps of conjugated polymers. Theoretical calculations have shed light on the nature of this trend, which may provide a unique class of conjugated polymers with promising optical and electronic properties.

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.

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.

Redox regulation of methionine in calmodulin affects the activity levels of senescence-related transcription factors in litchi.

Reactive oxygen species (ROS) play a role in aging and senescence in organisms. The oxidation of methionine (Met) residues in proteins to Met sulfoxide by ROS can cause conformational alteration and functional impairments. Met oxidation is reversed by Met sulfoxide reductase (Msr) A and B. Currently, the repair of oxidized proteins by Msr and Msr-mediated physiological functions are not well understood, especially in higher plants. The down-regulated expression of LcMsrA1/B1 may be involved in the senescence of litchi (Litchi chinensis) fruit. We verified that LcCaM1 is a substrate of LcMsrA1 and LcMsrB1 in vitro and in vivo, and oxidized LcCaM1 could be repaired by LcMsrA1 in combination with LcMsrB1. Moreover, LcMsrA1 and LcMsrB1 play important roles in repairing oxidized Met110 and Met125 residues, respectively, in LcCaM1. Furthermore, the Met oxidation in LcCaM1 did not affect its physical interactions with two LcCaM1-binding senescence-related transcription factors LcNAC13 and LcWRKY1, but enhanced their DNA-binding activities. Therefore, we hypothesized that the down-regulated expression of LcMsrA1/B1 results in the accelerated oxidation of LcCaM1, which enhanced the DNA-binding activities of LcNAC13 and LcWRKY1, thereby activating or repressing the expression of senescence-related genes.

Involvement of rice histone deacetylase HDA705 in seed germination and in response to ABA and abiotic stresses.

Histone acetylation and deacetylation play crucial roles in the modification of chromatin structure and regulation of gene expression in eukaryotes. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) assist to maintain the balance of chromatin acetylation status. Previous studies showed that plant HDACs are key regulators involved in response to development and stresses. In this study, we examined the expression pattern and function of HDA705, a member of the RPD3/HDA1-type HDAC in rice. Overexpression of HDA705 in rice decreased ABA and salt stress resistance during seed germination. Delayed seed germination of HDA705 overexpression lines was associated with down-regulated expression of GA biosynthetic genes and up-regulation of ABA biosynthetic genes. Moreover, overexpression of HDA705 in rice enhanced osmotic stress resistance during the seedling stage. Our findings demonstrate that HDA705 may play a role in regulating seed germination and the response to abiotic stresses in rice.