Suppression of Arabidopsis Mediator Subunit-Encoding MED18 Confers Broad Resistance Against DNA and RNA Viruses While MED25 Is Required for Virus Defense

The Mediator complex subunit MED25 interacts with HDA9 and PIF4 to regulate thermomorphogenesis

Thermomorphogenesis is, among other traits, characterized by enhanced hypocotyl elongation due to the induction of auxin biosynthesis genes like YUCCA8 by transcription factors, most notably PHYTOCHROME INTERACTING FACTOR 4 (PIF4). Efficient binding of PIF4 to the YUCCA8 locus under warmth depends on HISTONE DEACETYLASE 9 (HDA9) activity, which mediates histone H2A.Z depletion at the YUCCA8 locus. However, HDA9 lacks intrinsic DNA-binding capacity, and how HDA9 is recruited to YUCCA8, and possibly other PIF4-target sites, is currently not well understood. The Mediator complex functions as a bridge between transcription factors bound to specific promoter sequences and the basal transcription machinery containing RNA polymerase II. Mutants of Mediator component Mediator25 (MED25) exhibit reduced hypocotyl elongation and reduced expression of YUCCA8 at 27°C. In line with a proposed role for MED25 in thermomorphogenesis in Arabidopsis (Arabidopsis thaliana), we demonstrated an enhanced association of MED25 to the YUCCA8 locus under warmth and interaction of MED25 with both PIF4 and HDA9. Genetic analysis confirmed that MED25 and HDA9 operate in the same pathway. Intriguingly, we also showed that MED25 destabilizes HDA9 protein. Based on our findings, we propose that MED25 recruits HDA9 to the YUCCA8 locus by binding to both PIF4 and HDA9.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

Transcriptome dynamics underlying elicitor-induced defense responses against Septoria leaf spot disease of tomato (Solanum lycopersicum L.)

Elicitor-induced defense response against potential plant pathogens has been widely reported in several crop plants; however, transcriptome dynamics underlying such defense response remains elusive. Our previous study identified and characterized a novel elicitor, κ-carrageenan, from Kappaphycus alvarezii, a marine red seaweed. Our preliminary studies have shown that the elicitor-treatment enhances the tolerance of a susceptible tomato cultivar to Septoria lycopersici (causative agent of leaf spot disease). To gain further insights into the genes regulated during elicitor treatment followed by pathogen infection, we have performed RNA-Seq experiments under different treatments, namely, control (untreated and uninfected), elicitor treatment, pathogen infection alone, and elicitor treatment followed by pathogen infection. To validate the results, forty-three genes belonging to five different classes, namely, ROS activating and detoxifying enzyme encoding genes, DEAD-box RNA helicase genes, autophagy-related genes, cysteine proteases, and pathogenesis-related genes, were chosen. Expression profiling of each gene was performed using qRT-PCR, and the data was correlated with the RNA-seq data. Altogether, the study has pinpointed a repertoire of genes that could be potential candidates for further functional characterization to provide insights into novel elicitor-induced fungal defense and develop transgenic lines resistant to foliar diseases.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-021-00970-y.

Functional Analysis of OsMED16 and OsMED25 in Response to Biotic and Abiotic Stresses in Rice

Mediator complex is a multiprotein complex that regulates RNA polymerase II-mediated transcription. Moreover, it functions in several signaling pathways, including those involved in response to biotic and abiotic stresses. We used virus-induced gene silencing (VIGS) to study the functions of two genes, namely OsMED16 and OsMED25 in response to biotic and abiotic stresses in rice. Both genes were differentially induced by Magnaporthe grisea (M. grisea), the causative agent of blast disease, hormone treatment, and abiotic stress. We found that both BMV: OsMED16- and BMV: OsMED25-infiltrated seedlings reduced the resistance to M. grisea by regulating the accumulation of H₂O₂ and expression of defense-related genes. Furthermore, BMV: OsMED16-infiltrated seedlings decreased the tolerance to cold by increasing the malondialdehyde (MDA) content and reducing the expression of cold-responsive genes.

The Important Function of Mediator Complex in Controlling the Developmental Transitions in Plants

Developmental transitions in plants are tightly associated with changes in the transcriptional regulation of gene expression. One of the most important regulations is conferred by cofactors of RNA polymerase II including the mediator complex, a large complex with a modular organization. The mediator complex recruits transcription factors to bind to the specific sites of genes including protein-coding genes and non-coding RNA genes to promote or repress the transcription initiation and elongation using a protein-protein interaction module. Mediator complex subunits have been isolated and identified in plants and the function of most mediator subunits in whole life cycle plants have been revealed. Studies have shown that the Mediator complex is indispensable for the regulation of plant developmental transitions by recruiting age-, flowering-, or hormone-related transcription factors. Here, we first overviewed the Mediator subunits in plants, and then we summarized the specific Mediator subunits involved in developmental transitions, including vegetative phase change and floral transition. Finally, we proposed the future directions to further explore their roles in plants. The link between Mediator subunits and developmental transitions implies the necessity to explore targets of this complex as a potential application in developing high quality crop varieties.