The SMXL8-AGL9 module mediates crosstalk between strigolactone and gibberellin to regulate strigolactone-induced anthocyanin biosynthesis in apple.

Although the strigolactone (SL) signaling pathway and SL-mediated anthocyanin biosynthesis have been reported, the molecular association between SL signaling and anthocyanin biosynthesis remains unclear. In this study, we identified the SL signal transduction pathway associated with anthocyanin biosynthesis and the crosstalk between gibberellin (GA) and SL signaling in apple (Malus × domestica). ELONGATED HYPOCOTYL5 (HY5) acts as a key node integrating SL signaling and anthocyanin biosynthesis, and the SL response factor AGAMOUS-LIKE MADS-BOX9 (AGL9) promotes anthocyanin biosynthesis by activating HY5 transcription. The SL signaling repressor SUPPRESSOR OF MAX2 1-LIKE8 (SMXL8) interacts with AGL9 to form a complex that inhibits anthocyanin biosynthesis by downregulating HY5 expression. Moreover, the E3 ubiquitin ligase PROTEOLYSIS1 (PRT1) mediates the ubiquitination-mediated degradation of SMXL8, which is a key part of the SL signal transduction pathway associated with anthocyanin biosynthesis. In addition, the GA signaling repressor REPRESSOR-of-ga1-3-LIKE2a (RGL2a) mediates the crosstalk between GA and SL by disrupting the SMXL8-AGL9 interaction that represses HY5 transcription. Taken together, our study reveals the regulatory mechanism of SL-mediated anthocyanin biosynthesis and uncovers the role of SL-GA crosstalk in regulating anthocyanin biosynthesis in apple.

MdVQ10 promotes wound-triggered leaf senescence in association with MdWRKY75 and undergoes antagonistic modulation of MdCML15 and MdJAZs in apple.

Wounding stress leads to leaf senescence. However, the underlying molecular mechanism has not been elucidated. In this study, we investigated the role of the MdVQ10-MdWRKY75 module in wound-induced leaf senescence. MdWRKY75 was identified as a key positive modulator of wound-induced leaf senescence by activating the expression of the senescence-associated genes MdSAG12 and MdSAG18. MdVQ10 interacted with MdWRKY75 to enhance MdWRKY75-activated transcription of MdSAG12 and MdSAG18, thereby promoting leaf senescence triggered by wounding. In addition, the calmodulin-like protein MdCML15 promoted MdVQ10-mediated leaf senescence by stimulating the interaction between MdVQ10 and MdWRKY75. Moreover, the jasmonic acid signaling repressors MdJAZ12 and MdJAZ14 antagonized MdVQ10-mediated leaf senescence by weakening the MdVQ10-MdWRKY75 interaction. Our results demonstrate that the MdVQ10-MdWRKY75 module is a key modulator of wound-induced leaf senescence and provides insights into the mechanism of leaf senescence caused by wounding.

The MdNAC72-MdABI5 module acts as an interface integrating jasmonic acid and gibberellin signals and undergoes ubiquitination-dependent degradation regulated by MdSINA2 in apple.

Jasmonic acid (JA) and gibberellin (GA) coordinately regulate plant developmental programs and environmental cue responses. However, the fine regulatory network of the cross-interaction between JA and GA remains largely elusive. In this study, we demonstrate that MdNAC72 together with MdABI5 positively regulates anthocyanin biosynthesis through an exquisite MdNAC72-MdABI5-MdbHLH3 transcriptional cascade in apple. MdNAC72 interacts with MdABI5 to promote the transcriptional activation of MdABI5 on its target gene MdbHLH3 and directly activates the transcription of MdABI5. The MdNAC72-MdABI5 module regulates the integration of JA and GA signals in anthocyanin biosynthesis by combining with JA repressor MdJAZ2 and GA repressor MdRGL2a. MdJAZ2 disrupts the MdNAC72-MdABI5 interaction and attenuates the transcriptional activation of MdABI5 by MdNAC72. MdRGL2a sequesters MdJAZ2 from the MdJAZ2-MdNAC72 protein complex, leading to the release of MdNAC72. The E3 ubiquitin ligase MdSINA2 is responsive to JA and GA signals and promotes ubiquitination-dependent degradation of MdNAC72. The MdNAC72-MdABI5 interface fine-regulates the integration of JA and GA signals at the transcriptional and posttranslational levels by combining MdJAZ2, MdRGL2a, and MdSINA2. In summary, our findings elucidate the fine regulatory network connecting JA and GA signals with MdNAC72-MdABI5 as the core in apple.

Colorful hues: insight into the mechanisms of anthocyanin pigmentation in fruit.

Anthocyanin is a vital indicator for both fruit nutritional and commercial value. Anthocyanin accumulation is a surprisingly complicated process mediated by multiple networks associated with genetic, developmental, hormonal, and environmental factors. Transcriptional regulation along with epigenetic regulation constitutes the dominant molecular framework for anthocyanin biosynthesis. Here, we focus on current knowledge on regulatory mechanisms of anthocyanin accumulation, with emphasis on the latest progress in transcriptional and epigenetic regulation and the crosstalk between various signaling pathways. We present an emerging picture of how various internal and external stimuli control anthocyanin biosynthesis. Additionally, we discuss the synergistic or antagonistic effect of developmental, hormonal and environmental cues on anthocyanin accumulation in fruit.

Brassinosteroid signaling regulator BIM1 integrates brassinolide and jasmonic acid signaling during cold tolerance in apple.

Although brassinolide (BR) and jasmonic acid (JA) play essential roles in the regulation of cold stress responses, the molecular basis of their crosstalk remains elusive. Here, we show a key component of BR signaling in apple (Malus × domestica), BR INSENSITIVE1 (BRI1)-EMS-SUPPRESSOR1 (BES1)-INTERACTING MYC-LIKE PROTEIN1 (MdBIM1), increases cold tolerance by directly activating expression of C-REPEAT BINDING FACTOR1 (MdCBF1) and forming a complex with C-REPEAT BINDING FACTOR2 (MdCBF2) to enhance MdCBF2-activated transcription of cold-responsive genes. Two repressors of JA signaling, JAZMONATE ZIM-DOMAIN1 (MdJAZ1) and JAZMONATE ZIM-DOMAIN2 (MdJAZ2), interact with MdBIM1 to integrate BR and JA signaling under cold stress. MdJAZ1 and MdJAZ2 reduce MdBIM1-promoted cold stress tolerance by attenuating transcriptional activation of MdCBF1 expression by MdBIM1 and interfering with the formation of the MdBIM1-MdCBF2 complex. Furthermore, the E3 ubiquitin ligase ARABIDOPSIS TÓXICOS en LEVADURA73 (MdATL73) decreases MdBIM1-promoted cold tolerance by targeting MdBIM1 for ubiquitination and degradation. Our results not only reveal crosstalk between BR and JA signaling mediated by a JAZ-BIM1-CBF module but also provide insights into the posttranslational regulatory mechanism of BR signaling.

Tailoring Charge Separation in ZnIn2S4@CdS Hollow Nanocages for Simultaneous Alcohol Oxidation and CO2 Reduction under Visible Light.

Artificial photosynthesis provides a sustainable strategy for producing usable fuels and fine chemicals and attracts broad research interest. However, conventional approaches suffer from low reactivity or low selectivity. Herein, we demonstrate that photocatalytic reduction of CO2 coupled with selective oxidation of aromatic alcohol into corresponding syngas and aromatic aldehydes can be processed efficiently and fantastically over the designed S-scheme ZnIn2S4@CdS core-shell hollow nanocage under visible light. In the ZnIn2S4@CdS heterostructure, the photoexcited electrons and holes with weak redox capacities are eliminated, while the photoexcited electrons and holes with powder redox capacities are separated spatially and preserved on the desired active sites. Therefore, even if there are no cocatalysts and no vacancies, ZnIn2S4@CdS exhibits high reactivity. For instance, the CO production of ZnIn2S4@CdS is about 3.2 and 3.4 times higher than that of pure CdS and ZnIn2S4, respectively. More importantly, ZnIn2S4@CdS exhibits general applicability and high photocatalytic stability. Trapping agent experiments, 13CO2 isotopic tracing, in situ characterizations, and theoretical calculations reveal the photocatalytic mechanism. This study provides a new strategy to design efficient and selective photocatalysts for dual-function redox reactions by tailoring the active sites and regulating vector separation of photoexcited charge carriers.

Apple SINA11-JAZ2 module is involved in jasmonate signaling response.

The E3 ubiquitin ligase MdSINA11 targets the jasmonate ZIM domain protein MdJAZ2 for ubiquitination and degradation through the 26S proteasome pathway, thereby initiating jasmonate signaling and jasmonic acid-triggered anthocyanin biosynthesis in apple.

MdbHLH162 connects the gibberellin and jasmonic acid signals to regulate anthocyanin biosynthesis in apple.

Anthocyanins are secondary metabolites induced by environmental stimuli and developmental signals. The positive regulators of anthocyanin biosynthesis have been reported, whereas the anthocyanin repressors have been neglected. Although the signal transduction pathways of gibberellin (GA) and jasmonic acid (JA) and their regulation of anthocyanin biosynthesis have been investigated, the cross-talk between GA and JA and the antagonistic mechanism of regulating anthocyanin biosynthesis remain to be investigated. In this study, we identified the anthocyanin repressor MdbHLH162 in apple and revealed its molecular mechanism of regulating anthocyanin biosynthesis by integrating the GA and JA signals. MdbHLH162 exerted passive repression by interacting with MdbHLH3 and MdbHLH33, which are two recognized positive regulators of anthocyanin biosynthesis. MdbHLH162 negatively regulated anthocyanin biosynthesis by disrupting the formation of the anthocyanin-activated MdMYB1-MdbHLH3/33 complexes and weakening transcriptional activation of the anthocyanin biosynthetic genes MdDFR and MdUF3GT by MdbHLH3 and MdbHLH33. The GA repressor MdRGL2a antagonized MdbHLH162-mediated inhibition of anthocyanins by sequestering MdbHLH162 from the MdbHLH162-MdbHLH3/33 complex. The JA repressors MdJAZ1 and MdJAZ2 interfered with the antagonistic regulation of MdbHLH162 by MdRGL2a by titrating the formation of the MdRGL2a-MdbHLH162 complex. Our findings reveal that MdbHLH162 integrates the GA and JA signals to negatively regulate anthocyanin biosynthesis. This study provides new information for discovering more anthocyanin biosynthesis repressors and explores the cross-talk between hormone signals.

Apple SINA E3 ligase MdSINA3 negatively mediates JA-triggered leaf senescence by ubiquitinating and degrading the MdBBX37 protein.

Jasmonic acid (JA) induces chlorophyll degradation and leaf senescence. B-box (BBX) proteins play important roles in the modulation of leaf senescence, but the molecular mechanism of BBX protein-mediated leaf senescence remains to be further studied. Here, we identified the BBX protein MdBBX37 as a positive regulator of JA-induced leaf senescence in Malus domestica (apple). Further studies showed that MdBBX37 interacted with the senescence regulatory protein MdbHLH93 to enhance its transcriptional activation on the senescence-associated gene MdSAG18, thereby promoting leaf senescence. Moreover, the JA signaling repressor MdJAZ2 interacted with MdBBX37 and interfered with the interaction between MdBBX37 and MdbHLH93, thereby negatively mediating MdBBX37-promoted leaf senescence. In addition, the E3 ubiquitin ligase MdSINA3 delayed MdBBX37-promoted leaf senescence through targeting MdBBX37 for degradation. The MdJAZ2-MdBBX37-MdbHLH93-MdSAG18 and MdSINA3-MdBBX37 modules realized the precise modulation of JA on leaf senescence. In parallel, our data demonstrate that MdBBX37 was involved in abscisic acid (ABA)- and ethylene-mediated leaf senescence through interacting with the ABA signaling regulatory protein MdABI5 and ethylene signaling regulatory protein MdEIL1, respectively. Taken together, our results not only reveal the role of MdBBX37 as an integration node in JA-, ABA- and ethylene-mediated leaf senescence, but also provide new insights into the post-translational modification of BBX proteins.

The E3 ubiquitin ligases SINA1 and SINA2 integrate with the protein kinase CIPK20 to regulate the stability of RGL2a, a positive regulator of anthocyanin biosynthesis.

Although DELLA protein destabilization mediated by post-translational modifications is essential for gibberellin (GA) signal transduction and GA-regulated anthocyanin biosynthesis, the related mechanisms remain largely unknown. In this study, we report the ubiquitination and phosphorylation of an apple DELLA protein MdRGL2a in response to GA signaling and its regulatory role in anthocyanin biosynthesis. MdRGL2a could interact with MdWRKY75 to enhance the MdWRKY75-activated transcription of anthocyanin activator MdMYB1 and interfere with the interaction between anthocyanin repressor MdMYB308 and MdbHLH3 or MdbHLH33, thereby promoting anthocyanin accumulation. A protein kinase MdCIPK20 was found to phosphorylate and protect MdRGL2a from degradation, and it was essential for MdRGL2a-promoting anthocyanin accumulation. However, MdRGL2a and MdCIPK20 were ubiquitinated and degraded by E3 ubiquitin ligases MdSINA1 and MdSINA2, respectively, both of which were activated in the presence of GA. Our results display the integration of SINA1/2 with CIPK20 to dynamically regulate GA signaling and will be helpful toward understanding the mechanism of GA signal transduction and GA-inhibited anthocyanin biosynthesis. The discovery of extensive interactions between DELLA and SINA and CIPK proteins in apple will provide reference for the study of ubiquitination and phosphorylation of DELLA proteins in other species.

Phytochrome interacting factor MdPIF7 modulates anthocyanin biosynthesis and hypocotyl growth in apple.

Light affects many physiological and developmental processes of plants by regulating the expression and activity of light-responsive proteins. Among them, phytochrome interacting factors (PIFs) play pivotal roles in the regulation of anthocyanin accumulation and hypocotyl growth. However, the molecular mechanism is not well understood, especially in woody plants, such as apple (Malus × domestica). In this study, we identified a light-responsive PIF protein, MdPIF7, in apple and investigated the molecular mechanism of its regulation of anthocyanin biosynthesis and hypocotyl growth. We found that overexpression of MdPIF7 decreased anthocyanin accumulation in transgenic apple materials and promoted hypocotyl elongation in ectopically expressed Arabidopsis (Arabidopsis thaliana). Further investigation showed that MdPIF7 functioned by interacting with B-box 23 (MdBBX23), a positive regulator of anthocyanin biosynthesis in apple and hypocotyl growth inhibition in ectopically expressed Arabidopsis, and attenuating the transcriptional activation of MdBBX23 on LONG HYPOCOTYL 5 (MdHY5). In addition, MdPIF7 interacted with basic region leucine zipper 44 (MdbZIP44) and ethylene response factor 38 (MdERF38), two positive regulators of anthocyanin biosynthesis, and it negatively regulated MdbZIP44- and MdERF38-promoted anthocyanin accumulation by interfering with the interaction between MdbZIP44/MdERF38 and MdMYB1. Taken together, our results reveal that MdPIF7 regulates anthocyanin biosynthesis in apple and hypocotyl growth in ectopically expressed Arabidopsis through MdPIF7-MdBBX23-MdHY5 and MdPIF7-MdbZIP44/MdERF38-MdMYB1 modules. Our findings enrich the functional studies of PIF proteins and provide insights into the molecular mechanism of PIF-mediated anthocyanin biosynthesis and hypocotyl growth.

E3 ubiquitin ligases SINA4 and SINA11 regulate anthocyanin biosynthesis by targeting the IAA29-ARF5-1-ERF3 module in apple.

Auxin/indole-3-acetic acid (AUX/IAA) and auxin response factor (ARF) proteins are important components of the auxin signalling pathway, but their ubiquitination modification and the mechanism of auxin-mediated anthocyanin biosynthesis remain elusive. Here, the ARF MdARF5-1 was identified as a negative regulator of anthocyanin biosynthesis in apple, and it integrates auxin and ethylene signals by inhibiting the expression of the ethylene response factor MdERF3. The auxin repressor MdIAA29 decreased the inhibitory effect of MdARF5-1 on anthocyanin biosynthesis by attenuating the transcriptional inhibition of MdERF3 by MdARF5-1. In addition, the E3 ubiquitin ligases MdSINA4 and MdSINA11 played negative and positive regulatory roles in anthocyanin biosynthesis by targeting MdIAA29 and MdARF5-1 for ubiquitination degradation, respectively. MdSINA4 destabilized MdSINA11 to regulate anthocyanin accumulation in response to auxin signalling. In sum, our data revealed the crosstalk between auxin and ethylene signals mediated by the IAA29-ARF5-1-ERF3 module and provide new insights into the ubiquitination modification of the auxin signalling pathway.

Unlocking Dysprosium Constraints for China's 1.5 °C Climate Target.

Some key low-carbon technologies, ranging from wind turbines to electric vehicles, are underpinned by the strong rare-earth-based permanent magnets of the Nd, Pr (Dy)-Fe-Nb type (NdFeB). These NdFeB magnets, which are sensitive to demagnetization with temperature elevation (the Curie point), require the addition of variable amounts of dysprosium (Dy), where an elevation of the Curie point is needed to meet operational conditions. Given that China is the world's largest REE supplier with abundant REE reserves, the impact of an ambitious 1.5 °C climate target on China's Dy supply chain has sparked widespread concern. Here, we explore future trends and innovation strategies associated with the linkage between Dy and NdFeBs under various climate scenarios in China. We find China alone is expected to exhaust the global present Dy reserve within the next 2-3 decades to facilitate the 1.5 °C climate target. By implementing global available innovation strategies, such as material substitution, reduction, and recycling, it is possible to avoid 48%-68% of China's cumulative demand for Dy. Nevertheless, ongoing efforts in REE exploration and production are still required to meet China's growing Dy demand, which will face competition from the United States, European Union, and other countries with ambitious climate targets. Thus, our analysis urges China and those nations to form wider cooperation in REE supply chains as well as in NdFeB innovation for the realization of a global climate-safe future.

Progress in Photocurable 3D Printing of Photosensitive Polyurethane: A Review.

In recent years, as a class of advanced additive manufacturing (AM) technology, photocurable 3D printing has gained increasing attention. Based on its outstanding printing efficiency and molding accuracy, it is employed in various fields, such as industrial manufacturing, biomedical, soft robotics, electronic sensors. Photocurable 3D printing is a molding technology based on the principle of area-selective curing of photopolymerization reaction. At present, the main printing material suitable for this technology is the photosensitive resin, a composite mixture consisting of a photosensitive prepolymer, reactive monomer, photoinitiator, and other additives. As the technique research deepens and its application gets more developed, the design of printing materials suitable for different applications is becoming the hotspot. Specifically, these materials not only can be photocured but also have excellent properties, such as elasticity, tear resistance, fatigue resistance. Photosensitive polyurethanes can endow photocured resin with desirable performance due to their unique molecular structure including the inherent alternating soft and hard segments, and microphase separation. For this reason, this review summarizes and comments on the research and application progress of photocurable 3D printing of photosensitive polyurethanes, analyzing the advantages and shortcomings of this technology, also offering an outlook on this rapid development direction.

Truncated ERG Oncoproteins from TMPRSS2-ERG Fusions Are Resistant to SPOP-Mediated Proteasome Degradation.

SPOP mutations and TMPRSS2-ERG rearrangements occur collectively in up to 65% of human prostate cancers. Although the two events are mutually exclusive, it is unclear whether they are functionally interrelated. Here, we demonstrate that SPOP, functioning as an E3 ubiquitin ligase substrate-binding protein, promotes ubiquitination and proteasome degradation of wild-type ERG by recognizing a degron motif at the N terminus of ERG. Prostate cancer-associated SPOP mutations abrogate the SPOP-mediated degradation function on the ERG oncoprotein. Conversely, the majority of TMPRSS2-ERG fusions encode N-terminal-truncated ERG proteins that are resistant to the SPOP-mediated degradation because of degron impairment. Our findings reveal degradation resistance as a previously uncharacterized mechanism that contributes to elevation of truncated ERG proteins in prostate cancer. They also suggest that overcoming ERG resistance to SPOP-mediated degradation represents a viable strategy for treatment of prostate cancers expressing either mutated SPOP or truncated ERG.

Ectopic expression of MmCYP1A1, a mouse cytochrome P450 gene, positively regulates stress tolerance in apple calli and Arabidopsis.

KEY MESSAGE: Ectopic expression of MmCYP1A1 gene from Mus musculus in apple calli and Arabidopsis increased the levels of melatonin and 6-hydroxymelatonin, and improved their stress resistance. Melatonin occurs widely in organisms, playing a key regulatory role. CYP1A1 is a cytochrome P450 monooxygenase, involved in the melatonin metabolism, and is responsible for the synthesis of 6-hydroxymelatonin from melatonin. Melatonin and 6-hydroxymelatonin have strong antioxidant activities in animals. Here, we cloned MmCYP1A1 from Mus musculus and found that ectopic expression of MmCYP1A1 improved the levels of melatonin and 6-hydroxymelatonin in transgenic apple calli and Arabidopsis. Subsequently, we observed that MmCYP1A1 increased the tolerance of transgenic apple calli and Arabidopsis to osmotic stress simulated by polyethylene glycol 6000 (PEG 6000), as well as resistance of transgenic Arabidopsis to drought stress. Further, the number of lateral roots of MmCYP1A1 transgenic Arabidopsis were enhanced significantly after PEG 6000 treatment. The expression of MmCYP1A1 remarkably reduced malondialdehyde (MDA) content, electrolyte leakage, accumulation of H2O2 and O2- during stress treatment. Moreover, MmCYP1A1 enhanced stress tolerance in apple calli and Arabidopsis by increasing the expression levels of resistance genes. MmCYP1A1 also promoted stomatal closure in transgenic Arabidopsis to reduce leaf water loss during drought. Our results indicate that MmCYP1A1 plays a key role in plant stress tolerance, which may provide a reference for future plant stress tolerance studies.

Enhanced Acoustic Droplet Vaporization through the Active Magnetic Accumulation of Drug-Loaded Magnetic Particle-Encapsulated Nanodroplets (MPE-NDs) in Cancer Therapy.

The application of drug-loaded nanodroplets is still limited by their insufficient accumulation owing to the enhanced permeability and retention (EPR) effect failure in cancer therapy. To overcome these limitations, we propose an alternative magnetic particle-encapsulated nanodroplet (MPE-ND) with outstanding biosafety and magnetic targeting by encapsulating fluorinated Fe3O4-SiO2 nanoparticles inside the liquid core of the nanodroplets. Meanwhile, doxorubicin (DOX) can be stably loaded into the shell through both electrostatic and hydrophobic interactions to obtain drug-loaded MPE-NDs. Both in vitro and in vivo experiments have consistently demonstrated that drug-loaded MPE-NDs can significantly increase the local drug concentration and enhance the damage of tumor tissues through acoustic droplet vaporization under a static magnetic field (eADV therapy). Histological examination reveals that eADV therapy efficiently suppresses tumor proliferation by inducing apoptosis, destroying supply vessels, and inhibiting neovascularization. Drug-loaded MPE-NDs can be expected to open a new gateway for ultrasound-triggered drug delivery and cancer treatment.

The E3 ubiquitin ligase SINA1 and the protein kinase BIN2 cooperatively regulate PHR1 in apple anthocyanin biosynthesis.

PHR1 (PHOSPHATE STARVATION RESPONSE1) plays key roles in the inorganic phosphate (Pi) starvation response and in Pi deficiency-induced anthocyanin biosynthesis in plants. However, the post-translational regulation of PHR1 is unclear, and the molecular basis of PHR1-mediated anthocyanin biosynthesis remains elusive. In this study, we determined that MdPHR1 was essential for Pi deficiency-induced anthocyanin accumulation in apple (Malus × domestica). MdPHR1 interacted with MdWRKY75, a positive regulator of anthocyanin biosynthesis, to enhance the MdWRKY75-activated transcription of MdMYB1, leading to anthocyanin accumulation. In addition, the E3 ubiquitin ligase SEVEN IN ABSENTIA1 (MdSINA1) negatively regulated MdPHR1-promoted anthocyanin biosynthesis via the ubiquitination-mediated degradation of MdPHR1. Moreover, the protein kinase apple BRASSINOSTEROID INSENSITIVE2 (MdBIN2) phosphorylated MdPHR1 and positively regulated MdPHR1-mediated anthocyanin accumulation by attenuating the MdSINA1-mediated ubiquitination degradation of MdPHR1. Taken together, these findings not only demonstrate the regulatory role of MdPHR1 in Pi starvation induced anthocyanin accumulation, but also provide an insight into the post-translational regulation of PHR1.

MdABI5 works with its interaction partners to regulate abscisic acid-mediated leaf senescence in apple.

Abscisic acid (ABA) induces chlorophyll degradation and leaf senescence; however, the molecular mechanism remains poorly understood, especially in woody plants. In this study, we found that MdABI5 plays an essential role in the regulation of ABA-triggered leaf senescence in Malus domestica (apple). Through yeast screening, three transcription factors, MdBBX22, MdWRKY40 and MdbZIP44, were found to interact directly with MdABI5 in vitro and in vivo. Physiological and biochemical assays showed that MdBBX22 delayed leaf senescence in two pathways. First, MdBBX22 interacted with MdABI5 to inhibit the transcriptional activity of MdABI5 on the chlorophyll catabolic genes MdNYE1 and MdNYC1, thus negatively regulating chlorophyll degradation and leaf senescence. Second, MdBBX22 interacted with MdHY5 to interfere with the transcriptional activation of MdHY5 on MdABI5, thereby inhibiting the expression of MdABI5, which also contributed to the delay of leaf senescence. MdWRKY40 and MdbZIP44 were identified as positive regulators of leaf senescence. They accelerated MdABI5-promoted leaf senescence through the same regulatory pathways, i.e., interacting with MdABI5 to enhance the transcriptional activity of MdABI5 on MdNYE1 and MdNYC1. Taken together, our results suggest that MdABI5 works with its positive or negative interaction partners to regulate ABA-mediated leaf senescence in apple, in which it acts as a core regulator. The antagonistic regulation pathways ensure that plants respond to external stresses flexibly and efficiently. Our results provide a concept for further study on the regulation mechanisms of leaf senescence.

Jasmonate induces biosynthesis of anthocyanin and proanthocyanidin in apple by mediating the JAZ1-TRB1-MYB9 complex.

Jasmonate (JA) induces the biosynthesis of anthocyanin and proanthocyanidin. MdMYB9 is essential for modulating the accumulation of both anthocyanin and proanthocyanidin in apple, but the molecular mechanism for induction of anthocyanin and proanthocyanidin biosynthesis by JA is unclear. In this study, we discovered an apple telomere-binding protein (MdTRB1) to be the interacting protein of MdMYB9. A series of biological assays showed that MdTRB1 acted as a positive modulator of anthocyanin and proanthocyanidin accumulation, and is dependent on MdMYB9. MdTRB1 interacted with MdMYB9 and enhanced the activation activity of MdMYB9 to its downstream genes. In addition, we found that the JA signaling repressor MdJAZ1 interacted with MdTRB1 and interfered with the interaction between MdTRB1 and MdMYB9, therefore negatively modulating MdTRB1-promoted biosynthesis of anthocyanin and proanthocyanidin. These results show that the JAZ1-TRB1-MYB9 module dynamically modulates JA-mediated accumulation of anthocyanin and proanthocyanidin. Taken together, our data further expand the functional study of TRB1 and provide insights for further studies of the modulation of anthocyanin and proanthocyanidin biosynthesis by JA.