The Arabidopsis thaliana Mediator subunit MED8 regulates plant immunity to Botrytis Cinerea through interacting with the basic helix-loop-helix (bHLH) transcription factor FAMA

ERFVII-controlled hypoxia responses are in part facilitated by MEDIATOR SUBUNIT 25 in Arabidopsis thaliana

Flooding impairs plant growth through oxygen deprivation, which activates plant survival and acclimation responses. Transcriptional responses to low oxygen are generally associated with the activation of group VII ETHYLENE-RESPONSE FACTOR (ERFVII) transcription factors. However, the exact mechanisms and molecular components by which ERFVII factors initiate gene expression are not fully elucidated. Here, we show that the ERFVII factors RELATED TO APETALA 2.2 (RAP2.2) and RAP2.12 cooperate with the Mediator complex subunit AtMED25 to coordinate gene expression under hypoxia in Arabidopsis thaliana. Respective med25 knock-out mutants display reduced low-oxygen stress tolerance. AtMED25 physically associates with a distinct set of hypoxia core genes and its loss partially impairs transcription under hypoxia due to decreased RNA polymerase II recruitment. Association of AtMED25 with target genes requires the presence of ERFVII transcription factors. Next to ERFVII protein stabilisation, also the composition of the Mediator complex including AtMED25 is potentially affected by hypoxia stress as shown by protein-complex pulldown assays. The dynamic response of the Mediator complex to hypoxia is furthermore supported by the fact that two subunits, AtMED8 and AtMED16, are not involved in the establishment of hypoxia tolerance, whilst both act in coordination with AtMED25 under other environmental conditions. We furthermore show that AtMED25 function under hypoxia is independent of ethylene signalling. Finally, functional conservation at the molecular level was found for the MED25-ERFVII module between A. thaliana and the monocot species Oryza sativa, pointing to a potentially universal role of MED25 in coordinating ERFVII-dependent transcript responses to hypoxia in plants.

Bridging the Knowledge Gap: Utilization of Mediator Subunits for Crop Improvement

The Mediator complex is a multisubunit transcription coregulator that transfers regulatory signals from different transcription factors to RNA polymerase II (Pol II) to control Pol II-dependent transcription in eukaryotes. Studies on Arabidopsis Mediator subunits have revealed their unique or overlapping functions in various aspects of plant growth, stress adaptation and metabolite homeostasis. Therefore, the utilization of the plant Mediator complex for crop improvement has been of great interest. Advances in genome editing and sequencing techniques have expedited the characterization of Mediator subunits in economically important crops such as tomato, rice, wheat, soybean, sugarcane, pea, chickpea, rapeseed and hop. In this review, we summarize recent progress in understanding the molecular mechanisms of how the Mediator complex regulates crop growth, development and adaptation to environmental stress. We also discuss the conserved and diverse functions of the Mediator complex in different plant species. In addition, we propose several future research directions to deepen our understanding of the important roles of Mediator subunits and their interacting proteins, which would provide promising targets for genetic modification to develop new cultivars with desirable agronomic traits.

The Plant Mediator Complex in the Initiation of Transcription by RNA Polymerase II

Thirty years have passed since the discovery of the Mediator complex in yeast. We are witnessing breakthroughs and advances that have led to high-resolution structural models of yeast and mammalian Mediators in the preinitiation complex, showing how it is assembled and how it positions the RNA polymerase II and its C-terminal domain (CTD) to facilitate the CTD phosphorylation that initiates transcription. This information may be also used to guide future plant research on the mechanisms of Mediator transcriptional control. Here, we review what we know about the subunit composition and structure of plant Mediators, the roles of the individual subunits and the genetic analyses that pioneered Mediator research, and how transcription factors recruit Mediators to regulatory regions adjoining promoters. What emerges from the research is a Mediator that regulates transcription activity and recruits hormonal signaling modules and histone-modifying activities to set up an off or on transcriptional state that recruits general transcription factors for preinitiation complex assembly.

The role of cis-zeatin in enhancing high-temperature resistance and fucoxanthin biosynthesis in Phaeodactylum tricornutum

Phaeodactylum tricornutum a prominent source of industrial fucoxanthin production, faces challenges in its application due to its tolerance to high-temperature environments. This study investigates the physiological responses of P. tricornutum to high-temperature stress and its impact on fucoxanthin content, with a specific focus on the role of cis-zeatin. The results reveal that high-temperature stress inhibits P. tricornutum's growth and photosynthetic activity, leading to a decrease in fucoxanthin content. Transcriptome analysis shows that high temperature suppresses the expression of genes related to photosynthesis (e.g., psbO, psbQ, and OEC) and fucoxanthin biosynthesis (e.g., PYS, PDS1, and PSD2), underscoring the negative effects of high temperature on P. tricornutum. Interestingly, genes associated with cis-zeatin biosynthesis and cytokinesis signaling pathways exhibited increased expression under high-temperature conditions, indicating a potential role of cis-zeatin signaling in response to elevated temperatures. Content measurements confirm that high temperature enhances cis-zeatin content. Furthermore, the exogenous addition of cytokinesis mimetics or inhibitors significantly affected P. tricornutum's high-temperature resistance. Overexpression of the cis-zeatin biosynthetic enzyme gene tRNA DMATase enhanced P. tricornutum's resistance to high-temperature stress, while genetic knockout of tRNA DMATase reduced its resistance to high temperatures. Therefore, this research not only uncovers a novel mechanism for high-temperature resistance in P. tricornutum but also offers a possible alga species that can withstand high temperatures for the industrial production of fucoxanthin, offering valuable insights for practical utilization.IMPORTANCEThis study delves into Phaeodactylum tricornutum's response to high-temperature stress, specifically focusing on cis-zeatin. We uncover inhibited growth, reduced fucoxanthin, and significant cis-zeatin-related gene expression under high temperatures, highlighting potential signaling mechanisms. Crucially, genetic engineering and exogenous addition experiments confirm that the change in cis-zeatin levels could influence P. tricornutum's resistance to high-temperature stress. This breakthrough deepens our understanding of microalgae adaptation to high temperatures and offers an innovative angle for industrial fucoxanthin production. This research is a pivotal step toward developing heat-resistant microalgae for industrial use.

Pseudomonas syringae infectivity correlates to altered transcript and metabolite levels of Arabidopsis mediator mutants

Rapid metabolic responses to pathogens are essential for plant survival and depend on numerous transcription factors. Mediator is the major transcriptional co-regulator for integration and transmission of signals from transcriptional regulators to RNA polymerase II. Using four Arabidopsis Mediator mutants, med16, med18, med25 and cdk8, we studied how differences in regulation of their transcript and metabolite levels correlate to their responses to Pseudomonas syringae infection. We found that med16 and cdk8 were susceptible, while med25 showed increased resistance. Glucosinolate, phytoalexin and carbohydrate levels were reduced already before infection in med16 and cdk8, but increased in med25, which also displayed increased benzenoids levels. Early after infection, wild type plants showed reduced glucosinolate and nucleoside levels, but increases in amino acids, benzenoids, oxylipins and the phytoalexin camalexin. The Mediator mutants showed altered levels of these metabolites and in regulation of genes encoding key enzymes for their metabolism. At later stage, mutants displayed defective levels of specific amino acids, carbohydrates, lipids and jasmonates which correlated to their infection response phenotypes. Our results reveal that MED16, MED25 and CDK8 are required for a proper, coordinated transcriptional response of genes which encode enzymes involved in important metabolic pathways for Arabidopsis responses to Pseudomonas syringae infections.

Mediator subunit MED8 interacts with heat shock transcription factor HSF3 to promote fucoxanthin synthesis in the diatom Phaeodactylum tricornutum

Fucoxanthin, a natural carotenoid that has substantial pharmaceutical value due to its anticancer, antioxidant, antiobesity, and antidiabetic properties, is biosynthesized from glyceraldehyde-3-phosphate (G3P) via a series of enzymatic reactions. However, our understanding of the transcriptional mechanisms involved in fucoxanthin biosynthesis remains limited. Using reverse genetics, the med8 mutant was identified based on its phenotype of reduced fucoxanthin content, and the biological functions of MED8 in fucoxanthin synthesis were characterized using approaches such as gene expression, protein subcellular localization, protein-protein interaction and chromatin immunoprecipitation assay. Gene-editing mutants of MED8 exhibited decreased fucoxanthin content as well as reduced expression levels of six key genes involved in fucoxanthin synthesis, namely DXS, PSY1, ZDS-like, CRTISO5, ZEP1, and ZEP3, when compared to the wild-type (WT) strain. Furthermore, we showed that MED8 interacts with HSF3, and genetic analysis revealed their shared involvement in the genetic pathway governing fucoxanthin synthesis. Additionally, HSF3 was required for MED8 association with the promoters of the six fucoxanthin synthesis genes. In conclusion, MED8 and HSF3 are involved in fucoxanthin synthesis by modulating the expression of the fucoxanthin synthesis genes. Our results increase the understanding of the molecular regulation mechanisms underlying fucoxanthin synthesis in the diatom P. tricornutum.

OsMED16, a tail subunit of Mediator complex, interacts with OsE2Fa to synergistically regulate rice leaf development and blast resistance

Mediator, a universal eukaryotic coactivator, is a multiprotein complex to transduce information from the DNA-bound transcription factors to the RNA polymerase II transcriptional machinery. In this study, the biofunctions of a rice mediator subunit OsMED16 in leaf development and blast resistance were characterized. OsMED16 encodes a putative protein of 1170 amino acids, which is 393 bp shorted than the version in Rice Genome Annotation Project databases. Overexpression of OsMED16 plants exhibited wider leaves with larger and more numerous cells in lateral axis, and enhanced resistance to M. oryzae with hyperaccumulated salicylic acid. Further analysis revealed that OsMED16 interacts with OsE2Fa in nuclei, and the complex could directly regulate the transcriptional levels of several genes involved in cell cycle regulation and SA mediated blast resistance, such as OsCC52A1, OsCDKA1, OsCDKB2;2, OsICS1 and OsWRKY45. Altogether, this study proved that OsMED16 is a positive regulator of rice leaf development and blast resistance, and providing new insights into the crosstalk between cell cycle regulation and immunity.

MED8 regulates floral transition in Arabidopsis by interacting with FPA

Success in plant reproduction is highly dependent on the correct timing of the floral transition, which is tightly regulated by the flowering pathways. In the model plant Arabidopsis thaliana, the central flowering repressor FLOWERING LOCUS C (FLC) is precisely regulated by multiple flowering time regulators in the vernalization pathway and autonomous pathway, including FPA. Here we report that Arabidopsis MEDIATOR SUBUNIT 8 (MED8) promotes floral transition in Arabidopsis by recruiting FPA to the FLC locus to repress FLC expression. Loss of MED8 function leads to a significant late-flowering phenotype due to increased FLC expression. We further show that MED8 directly interacts with FPA in the nucleus and recruits FPA to the FLC locus. Moreover, MED8 is indispensable for FPA's function in controlling flowering time and regulating FLC expression. Our study thus reveals a flowering mechanism by which the Mediator subunit MED8 represses FLC expression by facilitating the binding of FPA to the FLC locus to ensure appropriate timing of flowering for reproductive success.

The Basic/Helix-Loop-Helix Transcription Factor Family Gene RcbHLH112 Is a Susceptibility Gene in Gray Mould Resistance of Rose (Rosa Chinensis)

The basic/helix-loop-helix (bHLH) family is a major family of transcription factors in plants. Although it has been reported that bHLH plays a defensive role against pathogen infection in plants, there is no comprehensive study on the bHLH-related defence response in rose (Rosa sp.). In this study, a genome-wide analysis of bHLH family genes (RcbHLHs) in rose was carried out, including their phylogenetic relationships, gene structure, chromosome localization and collinearity analysis. Via phylogenetic analysis, a total of 121 RcbHLH genes in the rose genome were divided into 21 sub-groups. These RcbHLHs are unevenly distributed in all 7 chromosomes of rose. The occurrence of gene duplication events indicates that whole-genome duplication and segmental duplication may play a key role in gene duplication. Ratios of non-synonymous to synonymous mutation frequency (Ka/Ks) analysis showed that the replicated RcbHLH genes mainly underwent purification selection, and their functional differentiation was limited. Gene expression analysis showed that 46 RcbHLHs were differentially expressed in rose petals upon B. cinerea infection. It is speculated that these RcbHLHs are candidate genes that regulate the response of rose plants to B. cinerea infection. Virus-induced gene silencing (VIGS) confirmed that RcbHLH112 in rose is a susceptibility factor for infection with B. cinerea. This study provides useful information for further study of the functions of the rose bHLH gene family.

The root-knot nematode effector MiMSP32 targets host 12-oxophytodienoate reductase 2 to regulate plant susceptibility

To establish persistent infections in host plants, herbivorous invaders, such as root-knot nematodes, must rely on effectors for suppressing damage-induced jasmonate-dependent host defenses. However, at present, the effector mechanisms targeting the biosynthesis of biologically active jasmonates to avoid adverse host responses are unknown. Using yeast two-hybrid, in planta co-immunoprecipitation, and mutant analyses, we identified 12-oxophytodienoate reductase 2 (OPR2) as an important host target of the stylet-secreted effector MiMSP32 of the root-knot nematode Meloidogyne incognita. MiMSP32 has no informative sequence similarities with other functionally annotated genes but was selected for the discovery of novel effector mechanisms based on evidence of positive, diversifying selection. OPR2 catalyzes the conversion of a derivative of 12-oxophytodienoate to jasmonic acid (JA) and operates parallel to 12-oxophytodienoate reductase 3 (OPR3), which controls the main pathway in the biosynthesis of jasmonates. We show that MiMSP32 targets OPR2 to promote parasitism of M. incognita in host plants independent of OPR3-mediated JA biosynthesis. Artificially manipulating the conversion of the 12-oxophytodienoate by OPRs increases susceptibility to multiple unrelated plant invaders. Our study is the first to shed light on a novel effector mechanism targeting this process to regulate the susceptibility of host plants.

NtbHLH49, a jasmonate-regulated transcription factor, negatively regulates tobacco responses to Phytophthora nicotianae

Tobacco black shank caused by Phytophthora nicotianae is a devastating disease that causes huge losses to tobacco production across the world. Investigating the regulatory mechanism of tobacco resistance to P. nicotianae is of great importance for tobacco resistance breeding. The jasmonate (JA) signaling pathway plays a pivotal role in modulating plant pathogen resistance, but the mechanism underlying JA-mediated tobacco resistance to P. nicotianae remains largely unclear. This work explored the P. nicotianae responses of common tobacco cultivar TN90 using plants with RNAi-mediated silencing of NtCOI1 (encoding the perception protein of JA signal), and identified genes involved in this process by comparative transcriptome analyses. Interestingly, the majority of the differentially expressed bHLH transcription factor genes, whose homologs are correlated with JA-signaling, encode AtBPE-like regulators and were up-regulated in NtCOI1-RI plants, implying a negative role in regulating tobacco response to P. nicotianae. A subsequent study on NtbHLH49, a member of this group, showed that it's negatively regulated by JA treatment or P. nicotianae infection, and its protein was localized to the nucleus. Furthermore, overexpression of NtbHLH49 decreased tobacco resistance to P. nicotianae, while knockdown of its expression increased the resistance. Manipulation of NtbHLH49 expression also altered the expression of a set of pathogen resistance genes. This study identified a set of genes correlated with JA-mediated tobacco response to P. nicotianae, and revealed the function of AtBPE-like regulator NtbHLH49 in regulating tobacco resistance to this pathogen, providing insights into the JA-mediated tobacco responses to P. nicotianae.

The Mediator Complex: A Central Coordinator of Plant Adaptive Responses to Environmental Stresses

As sessile organisms, plants are constantly exposed to a variety of environmental stresses and have evolved adaptive mechanisms, including transcriptional reprogramming, in order to survive or acclimate under adverse conditions. Over the past several decades, a large number of gene-specific transcription factors have been identified in the transcriptional regulation of plant adaptive responses. The Mediator complex plays a key role in transducing signals from gene-specific transcription factors to the transcription machinery to activate or repress target gene expression. Since its first purification about 15 years ago, plant Mediator complex has been extensively analyzed for its composition and biological functions. Mutants of many plant Mediator subunits are not lethal but are compromised in growth, development and response to biotic and abiotic stress, underscoring a particularly important role in plant adaptive responses. Plant Mediator subunits also interact with partners other than transcription factors and components of the transcription machinery, indicating the complexity of the regulation of gene expression by plant Mediator complex. Here, we present a comprehensive discussion of recent analyses of the structure and function of plant Mediator complex, with a particular focus on its roles in plant adaptive responses to a wide spectrum of environmental stresses and associated biological processes.

Phloroglucinol promotes fucoxanthin synthesis by activating the cis-zeatin and brassinolide pathways in Thalassiosira pseudonana

Phloroglucinol improves shoot formation and somatic embryogenesis in several horticultural and grain crops, but its function in microalgae remains unclear. Here, we found that sufficiently high concentrations of phloroglucinol significantly increased fucoxanthin synthesis, growth, and photosynthetic efficiency in the microalga Thalassiosira pseudonana. These results suggested that the role of phloroglucinol is conserved across higher plants and microalgae. Further analysis showed that, after phloroglucinol treatment, the contents of cis-zeatin and brassinolide in T. pseudonana increased significantly, while the contents of trans-zeatin, iP, auxin, or gibberellin were unaffected. Indeed, functional studies showed that the effects of cis-zeatin and brassinolide in T. pseudonana were similar to those of phloroglucinol. Knockout of key enzyme genes in the cis-zeatin synthesis pathway of T. pseudonana or treatment of T. pseudonana with a brassinolide synthesis inhibitor (brassinazole) significantly reduced growth and fucoxanthin content in T. pseudonana, and phloroglucinol treatment partially alleviated these inhibitory effects. However, phloroglucinol treatment was ineffective when the cis-zeatin and brassinolide pathways were simultaneously inhibited. These results suggested that the cis-zeatin and brassinolide signaling pathways are independent regulators of fucoxanthin synthesis in T. pseudonana, and that phloroglucinol affects both pathways. Thus, this study not only characterizes the mechanism by which phloroglucinol promotes fucoxanthin synthesis, but also demonstrates the roles of cis-zeatin and brassinolide in T. pseudonana. IMPORTANCE Here, we demonstrate that phloroglucinol, a growth promoter in higher plants, also increases growth and fucoxanthin synthesis in the microalga Thalassiosira pseudonana, and therefore may have substantial practical application for industrial fucoxanthin production. Phloroglucinol treatment also induced the synthesis of cis-zeatin and brassinolide in T. pseudonana, and the cis-zeatin and brassinolide signaling pathways were implicated in the phloroglucinol-driven increases in T. pseudonana growth and fucoxanthin synthesis. Thus, our work clarified the molecular mechanism of phloroglucinol promoting the growth and fucoxanthin synthesis of Thalassiosira pseudonana, and suggested that cis-zeatin and brassinolide, in addition to phloroglucinol, had potential utility as inducers of increased microalgal fucoxanthin production.

The Glutamate Receptor Plays a Role in Defense against Botrytis cinerea through Electrical Signaling in Tomato

Plant glutamate-like receptor genes (GLRs) are homologous to mammalian ionotropic glutamate receptors genes (iGluRs). Although GLRs have been implicated in plant defenses to biotic stress, the relationship between GLR-mediated plant immunity against fungal pathogens and electrical signals remains poorly understood. Here, we found that pretreatment with a GLR inhibitor, 6,7-dinitriquinoxaline-2,3-dione (DNQX), increased the susceptibility of tomato plants to the necrotrophic fungal pathogen Botrytis cinerea. Assessment of the glr3.3, glr3.5 and glr3.3/glr3.5 double-mutants upon B. cinerea infection showed that tomato GLR3.3 and GLR3.5 are essential for plant immunity against B. cinerea, wherein GLR3.3 plays the main role. Analysis of the membrane potential changes induced by glutamate (Glu) or glycine (Gly) revealed that amplitude was significantly reduced by knocking out GLR3.3 in tomato. While treatment with Glu or Gly significantly increased immunity against B. cinerea in wild-type plants, this effect was significantly attenuated in glr3.3 mutants. Thus, our data demonstrate that GLR3.3- and GLR3.5-mediated plant immunity against B. cinerea is associated with electrical signals in tomato plants.

Jasmonate regulates the FAMA/mediator complex subunit 8-THIOGLUCOSIDE GLUCOHYDROLASE 1 cascade and myrosinase activity

Myrosinases are β-thioglucoside glucosidases that are unique to the Brassicales order. These enzymes hydrolyze glucosinolates to produce compounds that have direct antibiotic effects or that function as signaling molecules in the plant immune system, protecting plants from pathogens and insect pests. However, the effects of jasmonic acid (JA), a plant hormone that is crucial for plant disease resistance, on myrosinase activity remain unclear. Here, we systematically studied the effects of JA on myrosinase activity and explored the associated internal transcriptional regulation mechanisms. Exogenous application of JA significantly increased myrosinase activity, while the inhibition of endogenous JA biosynthesis and signaling reduced myrosinase activity. In addition, some myrosinase genes in Arabidopsis (Arabidopsis thaliana) were upregulated by JA. Further genetic and biochemical evidence showed that transcription factor FAMA interacted with a series of JASMONATE ZIM-DOMAIN proteins and affected JA-mediated myrosinase activity. However, among the JA-upregulated myrosinase genes, only THIOGLUCOSIDE GLUCOHYDROLASE 1 (TGG1) was positively regulated by FAMA. Further biochemical analysis showed that FAMA bound to the TGG1 promoter to directly mediate TGG1 expression in conjunction with Mediator complex subunit 8 (MED8). Together, our results provide evidence that JA acts as an important signal upstream of the FAMA/MED8-TGG1 pathway to positively regulate myrosinase activity in Arabidopsis.

The Arabidopsis mediator complex subunit 8 regulates oxidative stress responses

Signaling events triggered by hydrogen peroxide (H2O2) regulate plant growth and defense by orchestrating a genome-wide transcriptional reprogramming. However, the specific mechanisms that govern H2O2-dependent gene expression are still poorly understood. Here, we identify the Arabidopsis Mediator complex subunit MED8 as a regulator of H2O2 responses. The introduction of the med8 mutation in a constitutive oxidative stress genetic background (catalase-deficient, cat2) was associated with enhanced activation of the salicylic acid pathway and accelerated cell death. Interestingly, med8 seedlings were more tolerant to oxidative stress generated by the herbicide methyl viologen (MV) and exhibited transcriptional hyperactivation of defense signaling, in particular salicylic acid- and jasmonic acid-related pathways. The med8-triggered tolerance to MV was manipulated by the introduction of secondary mutations in salicylic acid and jasmonic acid pathways. In addition, analysis of the Mediator interactome revealed interactions with components involved in mRNA processing and microRNA biogenesis, hence expanding the role of Mediator beyond transcription. Notably, MED8 interacted with the transcriptional regulator NEGATIVE ON TATA-LESS, NOT2, to control the expression of H2O2-inducible genes and stress responses. Our work establishes MED8 as a component regulating oxidative stress responses and demonstrates that it acts as a negative regulator of H2O2-driven activation of defense gene expression.

RNA polymerase II associated proteins regulate stomatal development through direct interaction with stomatal transcription factors in Arabidopsis thaliana

RNA polymerase II (Pol II) associated proteins (RPAPs) have been ascribed diverse functions at the cellular level; however, their roles in developmental processes in yeasts, animals and plants are very poorly understood. Through screening for interactors of NRPB3, which encodes the third largest subunit of Pol II, we identified RIMA, the orthologue of mammalian RPAP2. A combination of genetic and biochemical assays revealed the role of RIMA and other RPAPs in stomatal development in Arabidopsis thaliana. We show that RIMA is involved in nuclear import of NRPB3 and other Pol II subunits, and is essential for restraining division and for establishing cell identity in the stomatal cell lineage. Moreover, plant RPAPs IYO/RPAP1 and QQT1/RPAP4, which interact with RIMA, are also crucial for stomatal development. Importantly, RIMA and QQT1 bind physically to stomatal transcription factors SPEECHLESS, MUTE, FAMA and SCREAMs. The RIMA-QQT1-IYO complex could work together with key stomatal transcription factors and Pol II to drive cell fate transitions in the stomatal cell lineage. Direct interactions with stomatal transcription factors provide a novel mechanism by which RPAP proteins may control differentiation of cell types and tissues in eukaryotes.

Two marine natural products, penicillide and verrucarin J, are identified from a chemical genetic screen for neutral lipid accumulation effectors in Phaeodactylum tricornutum

There are a large number of valuable substances in diatoms, such as neutral lipid and pigments. However, due to the lack of clear metabolic pathways, their applications are still limited. Recently, chemical modulators are found to be powerful tools to investigate the metabolic pathways of neutral lipids. Thus, in this study, to identify new neutral lipid accumulation effectors, we screened the natural products that we separated before in the model diatom Phaeodactylum tricornutum (P. tricornutum) by using Nile-red staining method. Two compounds, penicillide and verrucarin J which were isolated from two marine fungal strains, were identified to promote neutral lipid accumulation. However, penicillide and verrucarin J were also found to significantly inhibit the growth of P. tricornutum through specifically inhibiting the photosynthesis of P. tricornutum. Quantitative analysis results showed that penicillide and verrucarin J significantly increased total lipid and triacylglycerol (TAG) contents, which are consistent with previous Nile-red staining results. The expression of key genes such as DGAT2D, GPAT2, LPAT2, and PAP involved in TAG synthesis and unsaturated fatty acids also increased after penicillide and verrucarin J treatments. Besides, many TAG-rich plastoglobuli formed in plastids shown by increased lipid droplets in the cytosol. Finally, penicillide and verrucarin J were found to reduce the expression of synthetic genes of fucoxanthin, and consequently reduced the content of fucoxanthin, indicating that there might be crosstalk between lipid metabolism and fucoxanthin metabolism. Thus, our work exhibits two useful compounds that could be used to further study the metabolic pathways of neutral lipid and fucoxanthin, which will fulfill the promise of diatoms as low cost, high value, sustainable feedstock for high-value products such as neutral lipid and pigments.

New Dihydroisocoumarin Root Growth Inhibitors From the Sponge-Derived Fungus Aspergillus sp. NBUF87

Six new dihydroisocoumarins, aspergimarins A-F (1-6), were discovered together with five known analogs (7-11) from a monoculture of the sponge-derived fungus Aspergillus sp. NBUF87. The structures of these compounds were elucidated through comprehensive spectroscopic methods, and absolute configurations were assigned after X-ray crystallography, use of the modified Mosher's method, and comparison of electronic circular dichroism (ECD) data with literature values for previously reported analogs. Compounds 1-11 were evaluated in a variety of bioassays, and at 100 μM, both 1 and 5 showed significant inhibitory effects on the lateral root growth of Arabidopsis thaliana Columbia-0 (Col-0). Moreover, at 100 μM, 5 also possessed notable inhibition against the primary root growth of Col-0. Meanwhile, 1-11 were all found to be inactive in vitro against acetylcholinesterase (AChE) (IC50 > 100 μM), four different types of human-derived cancer cell lines (IC50 > 50 μM), as well as methicillin-resistant Staphylococcus aureus and Escherichia coli (MIC > 50 μg/mL), and Plasmodium falciparum W2 (EC50 > 100 μg/mL), in phenotypic tests.

Morpho-Pathological and Global Transcriptomic Analysis Reveals the Robust Nonhost Resistance Responses in Chickpea Interaction with Alternaria brassicae

Alternaria blight, caused by Alternaria brassicae, causes considerable yield loss in Brassica crops. While several blight-resistant varieties have been developed using resistance sources from host germplasm, none of them are entirely successful in imparting durable resistance. This has prompted the exploration of novel gene pools of nonhost plant species. Nonhost resistance (NHR) is a durable form of resistance, comprising pre- and postinvasion layers of defense. We aimed to identify the molecular basis of NHR to A. brassicae and identify the layers of NHR operating in a nonhost, chickpea (Cicer arietinum). To elucidate the layers of NHR operating against A. brassicae, we compared the histopathology and infection patterns of A. brassicae in C. arietinum and Brassica juncea. Delayed conidial germination, impeded hyphal growth, suppressed appressorium formation, and limited hyphal penetration occurred in the nonhost plant compared with the host plant, implying the involvement of the preinvasion layer of NHR in C. arietinum. Next, we investigated the molecular basis of robust NHR, in C. arietinum challenged with A. brassicae, by microarray-based global transcriptome profiling. Genes involved in stomatal closure, cuticular wax biosynthesis, cell-wall modification, and secondary metabolite production (contributing to preinvasion NHR) as well as reactive oxygen species (ROS) and cell death (contributing to postinvasion NHR) were found to be upregulated. Consistent with transcriptomic analysis, the morpho-pathological analysis revealed stomatal closure, ROS accumulation, and localized cell death in C. arietinum as the defense strategies against A. brassicae. Thus, we identified NHR-contributing genes with potential applications in blight resistance gene transfer to B. juncea.

The Significance of the Intrinsically Disordered Regions for the Functions of the bHLH Transcription Factors

The bHLH proteins are a family of eukaryotic transcription factors regulating expression of a wide range of genes involved in cell differentiation and development. They contain the Helix-Loop-Helix (HLH) domain, preceded by a stretch of basic residues, which are responsible for dimerization and binding to E-box sequences. In addition to the well-preserved DNA-binding bHLH domain, these proteins may contain various additional domains determining the specificity of performed transcriptional regulation. According to this, the family has been divided into distinct classes. Our aim was to emphasize the significance of existing disordered regions within the bHLH transcription factors for their functionality. Flexible, intrinsically disordered regions containing various motives and specific sequences allow for multiple interactions with transcription co-regulators. Also, based on in silico analysis and previous studies, we hypothesize that the bHLH proteins have a general ability to undergo spontaneous phase separation, forming or participating into liquid condensates which constitute functional centers involved in transcription regulation. We shortly introduce recent findings on the crucial role of the thermodynamically liquid-liquid driven phase separation in transcription regulation by disordered regions of regulatory proteins. We believe that further experimental studies should be performed in this field for better understanding of the mechanism of gene expression regulation (among others regarding oncogenes) by important and linked to many diseases the bHLH transcription factors.

Proximity labeling of protein complexes and cell-type-specific organellar proteomes in Arabidopsis enabled by TurboID

Defining specific protein interactions and spatially or temporally restricted local proteomes improves our understanding of all cellular processes, but obtaining such data is challenging, especially for rare proteins, cell types, or events. Proximity labeling enables discovery of protein neighborhoods defining functional complexes and/or organellar protein compositions. Recent technological improvements, namely two highly active biotin ligase variants (TurboID and miniTurbo), allowed us to address two challenging questions in plants: (1) what are in vivo partners of a low abundant key developmental transcription factor and (2) what is the nuclear proteome of a rare cell type? Proteins identified with FAMA-TurboID include known interactors of this stomatal transcription factor and novel proteins that could facilitate its activator and repressor functions. Directing TurboID to stomatal nuclei enabled purification of cell type- and subcellular compartment-specific proteins. Broad tests of TurboID and miniTurbo in Arabidopsis and Nicotiana benthamiana and versatile vectors enable customization by plant researchers.

The plant Mediator complex and its role in jasmonate signaling

The Mediator complex is an essential, multisubunit transcriptional coactivator that is highly conserved in eukaryotes. Mediator interacts with gene-specific transcription factors, the RNA polymerase II transcriptional machinery, as well as several other factors involved in transcription, and acts as an integral hub to regulate various aspects of transcription. Recent studies of the plant Mediator complex have established that it functions in diverse aspects of plant development and fitness. Jasmonate (JA) is an oxylipin-derived plant hormone that regulates plant immunity and development. The basic helix-loop-helix transcription factor MYC2, which is a master regulator of JA signaling, orchestrates genome-wide transcriptional reprogramming of plant cells to coordinate defense- and growth-related processes. Here, we review the function of the plant Mediator complex in regulating JA signaling. We focus on the multifunctional Mediator subunit MED25, which emerges as an integrative hub for the transcriptional regulation of jasmonate signaling.