Biosynthesis, regulation, and biological significance of fumonisins in fungi: current status and prospects.

Fumonisins are one of the most important mycotoxin classes due to their widespread occurrence and potential health threat to humans and animals. Currently, most of the research focuses on the control of fumonisin contamination in the food supply chain. In recent years, significant progress in biochemistry, enzymology, and genetic regulation of fumonisin biosynthesis has been achieved using molecular technology. Furthermore, new insights into the roles of fumonisins in the interaction between fungi and plant hosts have been reported. This review provides an overview of the current understanding of the biosynthesis and regulation of fumonisins. The ecological significance of fumonisins to Fusarium species that produce the toxins is discussed, and the complex regulatory networks of fumonisin synthesis is proposed.

Biomass magnetic porous carbon prepared from mangosteen shell for the preconcentration of three bisphenols from beverages followed by liquid chromatography with quadrupole-Orbitrap high-resolution mass spectrometry determination.

Natural biomass magnetic porous carbon was successfully prepared via a cost-effective and green route using mangosteen shells as raw material. The prepared magnetic porous carbon was used as a magnetic solid-phase extraction adsorbent for bisphenols enrichment from beverages followed by high-performance liquid chromatography-quadrupole-Orbitrap high-resolution mass spectrometry. Parameters affecting extraction efficiency including sample solution pH, adsorbent amount, extraction time, eluent type, and volume were optimized. Results showed that biomass magnetic porous carbon had excellent adsorption properties for bisphenols due to its large specific surface area and abundant functional groups, which could form hydrogen bonding and π-π stacking with bisphenols. The enrichment factor of 3 bisphenols was in the range of 15-19. Under optimum conditions, favorable linearity for all analytes was obtained with correlation coefficients higher than 0.998. Recoveries of spiked samples were in the range of 88.5-105.1% with a relative standard deviation of 3.4-5.5%. These results demonstrated that magnetic porous carbon may be a promising adsorbent for the enrichment of aromatic compounds.

Shikonin-mediated PD-L1 degradation suppresses immune evasion in pancreatic cancer by inhibiting NF-κB/STAT3 and NF-κB/CSN5 signaling pathways.

BACKGROUND: Pancreatic cancer (PC) is a highly fatal malignancy with few effective therapies currently available. Recent studies have shown that PD-L1 inhibitors could be potential therapeutic targets for the treatment of PC. The present study aims to investigate the effect of Shikonin on immune evasion in PC with the involvement of the PD-L1 degradation. METHODS: Initially, the expression patterns of PD-L1 and NF-κB in PC were predicted in-silico using the GEPIA database, and were subsequently validated using PC tissues. Thereafter, the correlation of NF-κB with STAT3, CSN5 and PD-L1 was examined. PC cells were treated with Shikonin, NF-κB inhibitor, STAT3 activator, and CSN5 overexpression plasmid to investigate effects on PD-L1 glycosylation and immune evasion in PC. Finally, in vivo tumor formation was induced in C57BL/6J mice, in order to verify the in vitro results. RESULTS: PD-L1, NF-κB, NF-κB p65, STAT3, and CSN5 were highly expressed in PC samples, and NF-κB was positively correlated with STAT3/CSN5/PD-L1. Inhibition of NF-κB decreased PD-L1 glycosylation and increased PD-L1 degradation, whereas activated STAT3 and overexpressed CSN5 reversed these trends. Shikonin blocked immune evasion in PC, and lowered the expression of PD-L1, NF-κB, NF-κB p65, STAT3 and CSN5 in vivo and in vitro. CONCLUSION: The findings indicated Shikonin inhibited immune evasion in PC by inhibiting PD-L1 glycosylation and activating the NF-κB/STAT3 and NF-κB/CSN5 signaling pathways. These effects of Shikonin on PC cells may bear important potential therapeutic implications for the treatment of PC.

Alternative splicing of MaMYB16L regulates starch degradation in banana fruit during ripening.

The alternative splicing of select genes is an important mechanism to regulate responses to endogenous and environmental signals in plants. However, the role of alternative splicing in regulating fruit ripening remains unclear. Here, we discovered that MaMYB16L, an R1-type MYB transcription factor, undergoes alternative splicing and generates two transcripts, the full-length isoform MaMYB16L and a truncated form MaMYB16S, in banana fruit. During banana fruit ripening, the alternative splicing process intensifies with downregulated MaMYB16L and upregulated MaMYB16S. Moreover, MaMYB16L is a transcriptional repressor that directly binds with the promoters of many genes associated with starch degradation and MaDREB2, a positive ripening regulator, and represses their expression. In contrast, MaMBY16S lacks a DNA-binding domain but competitively combines and forms non-functional heterodimers with functional MaMYB16L. MaMYB16L-MaMYB16S heterodimers decrease the binding capacity and transrepression activity of MaMYB16L. The downregulation of MaMYB16L and the upregulation of MaMYB16S, that is, a decreased ratio of active to non-active isoforms, facilitates the activation of ripening-related genes and thereby promotes fruit ripening. Furthermore, the transient overexpression of MaMYB16S promotes banana fruit ripening, whereas the overexpression of MaMYB16L delays this process. Therefore, the alternative splicing of MaMYB16L might generate a self-controlled regulatory loop to regulate banana fruit ripening.

Downregulation of long non-coding RNA MAFG-AS1 represses tumorigenesis of colorectal cancer cells through the microRNA-149-3p-dependent inhibition of HOXB8.

BACKGROUND: Colorectal cancer (CRC) is considered as the second common death-induced cancer. More recently, association of long non-coding RNAs (lncRNAs) with CRC has been extensively investigated. Therefore, the present study was performed to determine whether lncRNA MAF BZIP Transcription Factor G Antisense RNA 1 (MAFG-AS1) could regulate biological activities of CRC cells and unravel the underlying mechanisms. METHODS: CRC and corresponding adjacent tissues were collected to determine the expression of lncRNA MAFG-AS1, microRNA-149-3p (miR-149-3p) and homeobox B8 (HOXB8) by RT-qPCR. Dual luciferase reporter gene assay was used to explore the targeting relationship between miR-149-3p and lncRNA MAFG-AS1 and between miR-149-3p and HOXB8, followed by RNA immunoprecipitation for verification. Migration, proliferation, invasion, and apoptosis of HCT116 and LoVo cells were examined when lncRNA MAFG-AS1 was silenced or miR-149-3p was overexpressed. Furthermore, tumorigenicity of HCT116 and LoVo cells was measured in vivo by tumor xenograft in nude mice. RESULTS: LncRNA MAFG-AS1 and HOXB8 were found to be highly expressed in CRC tissues and cells, while miR-149-3p was under-expressed. LncRNA MAFG-AS1 negatively regulated miR-149-3p while miR-149-3p downregulated HOXB8. In addition, lncRNA MAFG-AS1 silencing by shRNA or miR-149-3p upregulation by mimic suppressed the migration, proliferation, invasion and tumorigenesis but promoted the apoptosis of HCT116 and LoVo cells. CONCLUSION: Taken together, lncRNA MAFG-AS1 downregulation inhibits the malignant behaviors of CRC cells by upregulating miR-149-3p and downregulating HOXB8, providing a potential therapeutic target for CRC treatment.

Exogenous hydrogen sulfide protects fatty liver against ischemia-reperfusion injury by regulating endoplasmic reticulum stress-induced autophagy in macrophage through mediating the class A scavenger receptor pathway in rats.

Fatty liver disease is a disease manifested with excessive alcohol intake and obese. Importantly, hydrogen sulfide (H2 S) has been revealed to participate in the progression of fatty liver; however, the underlying mechanism has not been clearly elucidated yet. In this study, we aimed to investigate the effects of exogenous H2 S on fatty liver ischemia-reperfusion injury (IRI) through mediating class A scavenger receptor (SRA) pathway in rats. By determining endoplasmic reticulum stress (ERS)-related factors, autophagy markers and apoptosis-related factors in liver tissue and liver function, levels of oxidative stress, inflammatory factors, and hepatocyte apoptosis, the effects of H2 S on IRI-induced autophagy, oxidative stress, and inflammation were all examined in rat model of fatty liver IRI. Results from obtained data showed that H2 S decreased the expression of SRA, Grp78, PERK, CHOP, and Caspase-3, and increased that of LC3-II/LC3-I, in addition to alleviating the pathological changes of liver and reducing the levels of ALT, AST, LDH TBARS, and MDA. Moreover, H2 S decreased the levels of oxidative stress, the expression of pro-inflammatory factors including tumor necrosis factor α, interleukin 1, and interleukin 6, and the apoptosis of hepatocytes. Our findings suggested exogenous H2 S could reduce ERS by mediating the SRA pathway and protect liver function by inducing autophagy, and protect against IRI by reducing oxidative stress and inflammation.

Banana MaBZR1/2 associate with MaMPK14 to modulate cell wall modifying genes during fruit ripening.

KEY MESSAGE: Banana MaBZR1/2 interact with MaMPK14 to enhance the transcriptional inhibition of cell wall modifying genes including MaEXP2, MaPL2 and MaXET5. Fruit ripening and softening, the major attributes to perishability in fleshy fruits, are modulated by various plant hormones and gene expression. Banana MaBZR1/2, the central transcription factors of brassinosteroid (BR) signaling, mediate fruit ripening through regulation of ethylene biosynthesis, but their possible roles in fruit softening as well as the underlying mechanisms remain to be determined. In this work, we found that MaBZR1/2 directly bound to and repressed the promoters of several cell wall modifying genes such as MaEXP2, MaPL2 and MaXET5, whose transcripts were elevated concomitant with fruit ripening. Moreover, yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays indicated that MaBZR1/2 physically interacted with a mitogen-activated protein kinase MaMPK14, and this interaction strengthened the MaBZR1/2-mediated transcriptional inhibitory abilities. Collectively, our study provides insight into the mechanism of MaBZR1/2 contributing to fruit ripening and softening, which may have potential for banana molecular improvement.

MaMPK2 enhances MabZIP93-mediated transcriptional activation of cell wall modifying genes during banana fruit ripening.

Transcriptional regulation is an essential molecular machinery in controlling gene expression in diverse plant developmental processes including fruit ripening. This involves the interaction of transcription factors (TFs) and promoters of target genes. In banana, although a number of fruit ripening-associated TFs have been characterized, their number is relatively small. Here we identified a nuclear-localized basic leucine zipper (bZIP) TF, MabZIP93, associated with banana ripening. MabZIP93 activated cell wall modifying genes MaPL2, MaPE1, MaXTH23 and MaXGT1 by directly binding to their promoters. Transient over-expression of MabZIP93 in banana fruit resulted in the increased expression of MaPL2, MaPE1, MaXTH23 and MaXGT1. Moreover, a mitogen-activated protein kinase MaMPK2 and MabZIP93 were found to interact with MabZIP93. The interaction of MabZIP93 with MaMPK2 enhanced MabZIP93 activation of cell wall modifying genes, which was likely due to the phosphorylation of MabZIP93 mediated by MaMPK2. Overall, this study shows that MaMPK2 interacts with and phosphorylates MabZIP93 to promote MabZIP93-mediated transcriptional activation of cell wall modifying genes, thereby expanding our understanding of gene networks associated with banana fruit ripening.

Melatonin delays leaf senescence of Chinese flowering cabbage by suppressing ABFs-mediated abscisic acid biosynthesis and chlorophyll degradation.

Melatonin and abscisic acid (ABA) play contrasting roles in regulating leaf senescence in plants. The molecular mechanism underlying the interaction between melatonin and ABA involved in leaf senescence, however, remains poorly defined. Herein, we found that exogenous application of melatonin delayed the senescence of Chinese flowering cabbage, accompanied by reduced expression of chlorophyll catabolic and ABA biosynthetic genes, and a lower endogenous ABA level. Significantly, three nucleus-localized transcriptional activators BrABF1, BrABF4, and BrABI5 were identified, and their expressions were repressed by melatonin. In vitro and in vivo binding experiments revealed that BrABF1, BrABF4, and BrABI5 activated the transcription of a series of ABA biosynthetic and chlorophyll catabolic genes by physically binding to their promoters. Moreover, transient over-expression of BrABF1, BrABF4, and BrABI5 in tobacco leaves induced ABA accumulation and promoted chlorophyll degradation by upregulating tobacco ABA biosynthetic and chlorophyll catabolic genes, resulting in the accelerated leaf senescence. These effects were significantly attenuated by melatonin treatment. Our findings suggest that melatonin-mediated inhibition of leaf senescence involves suppression of ABFs-mediated ABA biosynthesis and chlorophyll degradation. Unraveling of the molecular regulatory mechanism of leaf senescence controlled by ABA and melatonin expands our understanding of the regulation of this phenomenon and offers potentially more effective molecular breeding strategies for extending the shelf-life of Chinese flowering cabbage.

Regulation of Long Non-Coding RNA-Dreh Involved in Proliferation and Migration of Hepatic Progenitor Cells during Liver Regeneration in Rats.

Liver regeneration plays a significant role in protecting liver function after liver injury or chronic liver disease. Long non-coding RNAs (lncRNAs) are considered to be involved in the proliferation of hepatocytes and liver regeneration. Therefore, this study aimed to explore the effects of LncRNA-Dreh on the regulation of hepatic progenitor cells (HPCs) during liver regeneration in rats. Initially, the rat model of liver injury was established to investigate the effect of LncRNA-Dreh down-regulation on liver tissues of rats with liver injury. Subsequently, HPCs line WB-F344 cells were transfected with interference plasmid of LncRNA-Dreh and the expression of LncRNA-Dreh and Vimentin was detected. The proliferation and migration ability of WB-F344 cells, as well as the content of albumin (ALB) and alpha fetoprotein (AFP) in cell differentiation were then determined. Disorderly arranged structure of liver tissue, a large number of HPCs set portal area as center extended to hepatic lobule and ductular reaction were observed in liver tissues of rats with liver injury. The expression of LncRNA-Dreh decreased while Vimentin increased in liver tissues of rats with liver injury. Moreover, the proliferation and migration ability, expression of Vimentin and AFP in WB-F344 cells were increased after silencing of LncRNA-Dreh and ALB was decreased. Collectively, our findings demonstrate that inhibition of LncRNA-Dreh can enhance the proliferation and migration abilities of HPCs in liver regeneration but cause abnormal differentiation of HPCs.

Activation of the Transcription of BrGA20ox3 by a BrTCP21 Transcription Factor Is Associated with Gibberellin-Delayed Leaf Senescence in Chinese Flowering Cabbage during Storage.

Several lines of evidence have implicated the involvement of the phytohormone gibberellin (GA) in modulating leaf senescence in plants. However, upstream transcription factors (TFs) that regulate GA biosynthesis in association with GA-mediated leaf senescence remain elusive. In the current study, we report the possible involvement of a TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) TF BrTCP21 in GA-delayed leaf senescence in Chinese flowering cabbage. Exogenous GA3 treatment maintained a higher value of maximum PSII quantum yield (Fv/Fm) and total chlorophyll content, accompanied by the repression of the expression of senescence-associated genes and chlorophyll catabolic genes, which led to the delay of leaf senescence. A class I member of TCP TFs BrTCP21, was further isolated and characterized. The transcript level of BrTCP21 was low in senescing leaves, and decreased following leaf senescence, while GA3 could keep a higher expression level of BrTCP21. BrTCP21 was further found to be a nuclear protein and exhibit trans-activation ability through transient-expression analysis in tobacco leaves. Intriguingly, the electrophoretic mobility shift assay (EMSA) and transient expression assay illustrated that BrTCP21 bound to the promoter region of a GA biosynthetic gene BrGA20ox3, and activated its transcription. Collectively, these observations reveal that BrTCP21 is associated with GA-delayed leaf senescence, at least partly through the activation of the GA biosynthetic pathway. These findings expand our knowledge on the transcriptional mechanism of GA-mediated leaf senescence.

BrTCP7 Transcription Factor Is Associated with MeJA-Promoted Leaf Senescence by Activating the Expression of BrOPR3 and BrRCCR.

The plant hormone jasmonic acid (JA) has been recognized as an important promoter of leaf senescence in plants. However, upstream transcription factors (TFs) that control JA biosynthesis during JA-promoted leaf senescence remain unknown. In this study, we report the possible involvement of a TEOSINTE BRANCHED1/CYCLOIDEA/PCF (TCP) TF BrTCP7 in methyl jasmonate (MeJA)-promoted leaf senescence in Chinese flowering cabbage. Exogenous MeJA treatment reduced maximum quantum yield (Fv/Fm) and total chlorophyll content, accompanied by the increased expression of senescence marker and chlorophyll catabolic genes, and accelerated leaf senescence. To further understand the transcriptional regulation of MeJA-promoted leaf senescence, a class I member of TCP TFs BrTCP7 was examined. BrTCP7 is a nuclear protein and possesses trans-activation ability through subcellular localization and transcriptional activity assays. A higher level of BrTCP7 transcript was detected in senescing leaves, and its expression was up-regulated by MeJA. The electrophoretic mobility shift assay and transient expression assay showed that BrTCP7 binds to the promoter regions of a JA biosynthetic gene BrOPR3 encoding OPDA reductase3 (OPR3) and a chlorophyll catabolic gene BrRCCR encoding red chlorophyll catabolite reductase (RCCR), activating their transcriptions. Taken together, these findings reveal that BrTCP7 is associated with MeJA-promoted leaf senescence at least partly by activating JA biosynthesis and chlorophyll catabolism, thus expanding our knowledge of the transcriptional mechanism of JA-mediated leaf senescence.

Pitaya HpWRKY3 Is Associated with Fruit Sugar Accumulation by Transcriptionally Modulating Sucrose Metabolic Genes HpINV2 and HpSuSy1.

Sugar level is an important determinant of fruit taste and consumer preferences. However, upstream regulators that control sugar accumulation during fruit maturation are poorly understood. In the present work, we found that glucose is the main sugar in mature pitaya (Hylocereus) fruit, followed by fructose and sucrose. Expression levels of two sucrose-hydrolyzing enzyme genes HpINV2 and HpSuSy1 obviously increased during fruit maturation, which were correlated well with the elevated accumulation of glucose and fructose. A WRKY transcription factor HpWRKY3 was further identified as the putative binding protein of the HpINV2 and HpSuSy1 promoters by yeast one-hybrid and gel mobility shift assays. HpWRKY3 was localized exclusively in the nucleus and possessed trans-activation ability. HpWRKY3 exhibited the similar expression pattern with HpINV2 and HpSuSy1. Finally, transient expression assays in tobacco leaves showed that HpWRKY3 activated the expressions of HpINV2 and HpSuSy1. Taken together, we propose that HpWRKY3 is associated with pitaya fruit sugar accumulation by activating the transcriptions of sucrose metabolic genes. Our findings thus shed light on the transcriptional mechanism that regulates the sugar accumulation during pitaya fruit quality formation.

Differential Accumulation of Aroma Compounds in Normal Green and Albino-Induced Yellow Tea (Camellia sinensis) Leaves.

Tea (Camellia sinensis) cultivars with green leaves are the most widely used for making tea. Recently, tea mutants with white or yellow young shoots have attracted increasing interest as raw materials for making "high-quality" tea products. Albino teas are generallycharacterized as having metabolites of relatively high amino acid content and lower catechin content. However, little is known about aroma compounds in albino tea leaves. Herein, we compared original normal leaves (green) and light-sensitive albino leaves (yellow) of cv. Yinghong No. 9. GC-MS was employed to analyze endogenous tea aroma compounds and related precursors. Quantitative real time PCR was used to measure expression levels of genes involved in biosyntheses of tea aromas.The total contents of most endogenous free tea aromas, including aroma fatty acid derivatives, aroma terpenes, and aroma phenylpropanoids/benzenoids, and their glycosidically bound aroma compounds, were lower in yellow leaves than in green leaves. The content of the key precursor geranyl diphosphate (GDP) and expression levels of key synthetic genes involved in the formation of linalool, a major aroma compound in cv. Yinghong No. 9, were investigated. Linalool content was lower in albino-induced yellow leaves, which was due to the lower GDP content compared with normal green leaves.

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.

Optimization of the Production of 1-Phenylethanol Using Enzymes from Flowers of Tea (Camellia sinensis) Plants.

1-Phenylethanol (1PE) can be used as a fragrance in food flavoring and cosmetic industries and as an intermediate in the pharmaceutical industry. 1PE can be synthesized from acetophenone, and the cost of 1PE is higher than the cost of acetophenone. Therefore, it is important to establish an effective and low-cost approach for producing 1PE. Our previous studies found that tea (Camellia sinensis) flowers, which are an abundant and waste resource, contained enzymes that could transform acetophenone to 1PE. In the present study, we extracted crude enzymes from tea flowers and optimized the production conditions of 1PE using response surface methodology. The optimized conditions were an extraction pH of 7.0, a reaction pH of 5.3, a reaction temperature of 55 °C, a reaction time of 100 min, a coenzyme NADPH concentration of 3.75 µmol/mL in the reaction assay, and a substrate acetophenone concentration of 1.25 µmol/mL in the reaction assay. The results provide essential information for future industrial 1PE production using plant-derived enzymes.

Recent Advances in the Emission and Functions of Plant Vegetative Volatiles.

Plants synthesize and emit a large variety of volatile organic compounds, which possess extremely important ecological functions. In most case, most plant volatiles are liquids, rather than gases, at room temperature. Some volatiles are emitted "on demand" when plants, especially vegetative parts, are exposed to abiotic or biotic stress. In this review, we summarize some of the highlights of plant vegetative volatile emission and functions research published during the past few years.

Elucidation of Differential Accumulation of 1-Phenylethanol in Flowers and Leaves of Tea (Camellia sinensis) Plants.

1-Phenylethanol (1PE) is a major aromatic volatile in tea (Camellia sinensis) flowers, whereas it occurs in a much smaller amounts in leaves. Enzymes involved in the formation of 1PE in plants and the reason why 1PE differentially accumulates in plants is unknown. In the present study, enzymes in the last step leading from acetophenone to 1PE were isolated from tea flowers by traditional biochemical chromatography. The two types of partially purified enzymes were proposed to be responsible for formations of (R)-1PE and (S)-1PE, respectively. Tea leaves also contained such enzymes having equivalent activities with flowers. Stable isotope labeling experiments indicated that weak transformation from l-phenylalanine to acetophenone in leaves mainly resulted in little occurrence of 1PE in leaves. This study provided an example that differential distribution of some metabolites in plant tissues was not only determined by enzyme(s) in the last step of metabolite formation, but also can be due to substrate availability.

ATP homeostasis and signaling in plants.

ATP is the primary form of energy for plants, and a shortage of cellular ATP is generally acknowledged to pose a threat to plant growth and development, stress resistance, and crop quality. The overall metabolic processes that contribute to the ATP pool, from production, dissipation, and transport to elimination, have been studied extensively. Considerable evidence has revealed that in addition to its role in energy supply, ATP also acts as a regulatory signaling molecule to activate global metabolic responses. Identification of the eATP receptor DORN1 contributed to a better understanding of how plants cope with disruption of ATP homeostasis and of the key points at which ATP signaling pathways intersect in cells or whole organisms. The functions of SnRK1α, the master regulator of the energy management network, in restoring the equilibrium of the ATP pool have been demonstrated, and the vast and complex metabolic network mediated by SnRK1α to adapt to fluctuating environments has been characterized. This paper reviews recent advances in understanding the regulatory control of the cellular ATP pool and discusses possible interactions among key regulators of ATP-pool homeostasis and crosstalk between iATP/eATP signaling pathways. Perception of ATP deficit and modulation of cellular ATP homeostasis mediated by SnRK1α in plants are discussed at the physiological and molecular levels. Finally, we suggest future research directions for modulation of plant cellular ATP homeostasis.

Banana MabHLH28 positively regulates the expression of softening-related genes to mediate fruit ripening independently or via cooperating with MaWRKY49/111.

Texture softening is a physiological indicator of fruit ripening, which eventually contributes to fruit quality and the consumer's acceptance. Despite great progress having been made in identification of the genes related to fruit softening, the upstream transcriptional regulatory pathways of these softening-related genes are not fully elucidated. Here, a novel bHLH gene, designated as MabHLH28, was identified because of its significant upregulation in banana fruit ripening. DAP-Seq analysis revealed that MabHLH28 bound to the core sequence of 'CAYGTG' presented in promoter regions of fruit softening-associated genes, such as the genes related to cell wall modification (MaPG3, MaPE1, MaPL5, MaPL8, MaEXP1, MaEXP2, MaEXPA2, and MaEXPA15) and starch degradation (MaGWD1 and MaLSF2), and these bindings were validated by EMSA and DLR assays. Transient overexpression and knockdown of MabHLH28 in banana fruit resulted in up- and down-regulation of softening-related genes, thereby hastening and postponing fruit ripening. Furthermore, overexpression of MabHLH28 in tomato accelerated the ripening process by elevating the accumulation of softening-associated genes. In addition, MabHLH28 showed interaction withMaWRKY49/111 and itself to form protein complexes, which could combinatorically strengthen the transcription of softening-associated genes. Taken together, our findings suggest that MabHLH28 mediates fruit softening by upregulating the expression of softening-related genes either alone or in combination with MaWRKY49/111.