Transcriptional regulation of plant innate immunity

OsEIL2 balances rice immune responses against (hemi)biotrophic and necrotrophic pathogens via the salicylic acid and jasmonic acid synergism

Plants typically activate distinct defense pathways against various pathogens. Heightened resistance to one pathogen often coincides with increased susceptibility to another pathogen. However, the underlying molecular basis of this antagonistic response remains unclear. Here, we demonstrate that mutants defective in the transcription factor ETHYLENE-INSENSITIVE 3-LIKE 2 (OsEIL2) exhibited enhanced resistance to the biotrophic bacterial pathogen Xanthomonas oryzae pv oryzae and to the hemibiotrophic fungal pathogen Magnaporthe oryzae, but enhanced susceptibility to the necrotrophic fungal pathogen Rhizoctonia solani. Furthermore, necrotroph-induced OsEIL2 binds to the promoter of OsWRKY67 with high affinity, leading to the upregulation of salicylic acid (SA)/jasmonic acid (JA) pathway genes and increased SA/JA levels, ultimately resulting in enhanced resistance. However, biotroph- and hemibiotroph-induced OsEIL2 targets OsERF083, resulting in the inhibition of SA/JA pathway genes and decreased SA/JA levels, ultimately leading to reduced resistance. Our findings unveil a previously uncharacterized defense mechanism wherein two distinct transcriptional regulatory modules differentially mediate immunity against pathogens with different lifestyles through the transcriptional reprogramming of phytohormone pathway genes.

Antagonistic control of rice immunity against distinct pathogens by the two transcription modules via salicylic acid and jasmonic acid pathways

Although the antagonistic effects of host resistance against biotrophic and necrotrophic pathogens have been documented in various plants, the underlying mechanisms are unknown. Here, we investigated the antagonistic resistance mediated by the transcription factor ETHYLENE-INSENSITIVE3-LIKE 3 (OsEIL3) in rice. The Oseil3 mutant confers enhanced resistance to the necrotroph Rhizoctonia solani but greater susceptibility to the hemibiotroph Magnaporthe oryzae and biotroph Xanthomonas oryzae pv. oryzae. OsEIL3 directly activates OsERF040 transcription while repressing OsWRKY28 transcription. The infection of R. solani and M. oryzae or Xoo influences the extent of binding of OsEIL3 to OsWRKY28 and OsERF040 promoters, resulting in the repression or activation of both salicylic acid (SA)- and jasmonic acid (JA)-dependent pathways and enhanced susceptibility or resistance, respectively. These results demonstrate that the distinct effects of plant immunity to different pathogen types are determined by two transcription factor modules that control transcriptional reprogramming and the SA and JA pathways.

A close-up of regulatory networks and signaling pathways of MKK5 in biotic and abiotic stresses

Mitogen-activated protein Kinase Kinase 5 (MKK5) is a central hub in the complex phosphorylation chain reaction of the Mitogen-activated protein kinases (MAPK) cascade, regulating plant responses to biotic and abiotic stresses. This review manuscript aims to provide a comprehensive analysis of the regulatory mechanism of the MKK5 involved in stress adaptation. This review will delve into the intricate post-transcriptional and post-translational modifications of the MKK5, discussing how they affect its expression, activity, and subcellular localization in response to stress signals. We also discuss the integration of the MKK5 into complex signaling pathways, orchestrating plant immunity against pathogens and its modulating role in regulating abiotic stresses, such as: drought, cold, heat, and salinity, through the phytohormonal signaling pathways. Furthermore, we highlight potential applications of the MKK5 for engineering stress-resilient crops and provide future perspectives that may pave the way for future studies. This review manuscript aims to provide valuable insights into the mechanisms underlying MKK5 regulation, bridge the gap from numerous previous findings, and offer a firm base in the knowledge of MKK5, its regulating roles, and its involvement in environmental stress regulation.

The rice E3 ubiquitin ligase-transcription factor module targets two trypsin inhibitors to enhance broad-spectrum disease resistance

Broad-spectrum disease resistance (BSR) is crucial for controlling plant diseases and relies on immune signals that are subject to transcriptional and post-translational regulation. How plants integrate and coordinate these signals remains unclear. We show here that the rice really interesting new gene (RING)-type E3 ubiquitin ligase OsRING113 targets APIP5, a negative regulator of plant immunity and programmed cell death (PCD), for 26S proteasomal degradation. The osring113 mutants in Nipponbare exhibited decreased BSR, while the overexpressing OsRING113 plants showed enhanced BSR against Magnaporthe oryzae (M. oryzae) and Xanthomonas oryzae pv. oryzae (Xoo). Furthermore, APIP5 directly suppressed the transcription of the Bowman-Birk trypsin inhibitor genes OsBBTI5 and AvrPiz-t-interacting protein 4 (APIP4). Overexpression of these two genes, which are partially required for APIP5-mediated PCD and disease resistance, conferred BSR. OsBBTI5 and APIP4 associated with and stabilized the pathogenesis-related protein OsPR1aL, which promotes M. oryzae resistance. Our results identify an immune module with integrated and coordinated hierarchical regulations that confer BSR in plants.

Transcription Factor Pdr3p Promotes Carotenoid Biosynthesis by Activating GAL Promoters in Saccharomyces cerevisiae

Pleiotropic drug resistance (PDR) family proteins have been extensively studied for their roles in transporting hydrophobic substances, including carotenoids. Overexpression of the PDR family regulator Pdr3p was recently found to boost the biosynthesis of carotenoids, which could not be explained by enhanced product secretion due to the meager extracellular proportions. To provide insights into the possible mechanism, comparative transcriptomics, reverse metabolic engineering, and electrophoretic mobility shift assay (EMSA) were conducted. Transcriptomic data suggested an unexpected correlation between Pdr3p overexpression and the transcriptional levels of GAL promoter-driven genes. This assumption was verified using mCherry and the lycopene synthetic pathway as the reporters. qRT-PCR and EMSA provided further evidence for the activation of GAL promoters by Pdr3p binding to their upstream activation sequences (UASs). This work gives insight into the mechanism of Pdr3p-promoted carotenoid production and highlights the complicated metabolic networking between transcriptional factors and promoters in yeast.

Cell-type-specific responses to fungal infection in plants revealed by single-cell transcriptomics

Pathogen infection is a dynamic process. Here, we employ single-cell transcriptomics to investigate plant response heterogeneity. By generating an Arabidopsis thaliana leaf atlas encompassing 95,040 cells during infection by a fungal pathogen, Colletotrichum higginsianum, we unveil cell-type-specific gene expression, notably an enrichment of intracellular immune receptors in vasculature cells. Trajectory inference identifies cells that had different interactions with the invading fungus. This analysis divulges transcriptional reprogramming of abscisic acid signaling specifically occurring in guard cells, which is consistent with a stomatal closure dependent on direct contact with the fungus. Furthermore, we investigate the transcriptional plasticity of genes involved in glucosinolate biosynthesis in cells at the fungal infection sites, emphasizing the contribution of the epidermis-expressed MYB122 to disease resistance. This work underscores spatially dynamic, cell-type-specific plant responses to a fungal pathogen and provides a valuable resource that supports in-depth investigations of plant-pathogen interactions.

Genome-wide characterization of the PLATZ gene family in watermelon (Citrullus lanatus L.) with putative functions in biotic and abiotic stress response

Plant AT-rich sequence and zinc-binding (PLATZ) proteins are plant-specific transcription factors involved in growth, development, and stress responses. Here, we conducted a genome-wide characterization of the watermelon ClPLATZ family and examined its expression responsiveness to defense hormones and pathogen infection along with putative functions in biotic and abiotic stress responses. The watermelon genome contains 12 putative ClPLATZ genes, encoding proteins with a characteristic PLATZ domain, and their promoters contain various cis-elements related to plant growth, development, phytohormones and stress response. The ClPLATZ genes, except ClPLATZ6, are differentially expressed in response to defense hormones (e.g., salicylic acid and methyl jasmonate) and fungal infections caused by Fusarium oxysporum f. sp. niveum and Stagonosporopsis cucurbitacearum. Most ClPLATZ proteins interact with other proteins (viz., ClDP, ClRPT2a, and ClRPC53). Among ClPLATZ proteins, ClPLATZ8, 9, 10, and 11 are predominately localized in the nucleus. ClPLATZ3 and 8 positively, but ClPLATZ11 negatively regulate resistance against Pseudomonas syringe pv. tomato DC3000 in transgenic Arabidopsis lines. ClPLATZ8 and 11 positively regulate stress tolerance to NaCl and mannitol during seed germination in transgenic Arabidopsis. In conclusion, the characterization of the ClPLATZ family provides insights into the biological functions of ClPLATZ genes in growth, development, and stress response in watermelon. Further, the involvement of certain ClPLATZ genes in biotic and abiotic stress response in transgenic Arabidopsis suggests their potential application in engineering stress-tolerant crops.

Tight genetic linkage of genes causing hybrid necrosis and pollinator isolation between young species

The mechanisms of reproductive isolation that cause phenotypic diversification and eventually speciation are a major topic of evolutionary research. Hybrid necrosis is a post-zygotic isolation mechanism in which cell death develops in the absence of pathogens. It is often due to the incompatibility between proteins from two parents. Here we describe a unique case of hybrid necrosis due to an incompatibility between loci on chromosomes 2 and 7 between two pollinator-isolated Petunia species. Typical immune responses as well as endoplasmic reticulum stress responses are induced in the necrotic line. The locus on chromosome 2 encodes ChiA1, a bifunctional GH18 chitinase/lysozyme. The enzymatic activity of ChiA1 is dispensable for the development of necrosis. We propose that the extremely high expression of ChiA1 involves a positive feedback loop between the loci on chromosomes 2 and 7. ChiA1 is tightly linked to major genes involved in the adaptation to different pollinators, a form of pre-zygotic isolation. This linkage of pre- and post-zygotic barriers strengthens reproductive isolation and probably contributes to rapid diversification and speciation.

Tuning the Wavelength: Manipulation of Light Signaling to Control Plant Defense

The growth-defense trade-off in plants is a phenomenon whereby plants must balance the allocation of their resources between developmental growth and defense against attack by pests and pathogens. Consequently, there are a series of points where growth signaling can negatively regulate defenses and where defense signaling can inhibit growth. Light perception by various photoreceptors has a major role in the control of growth and thus many points where it can influence defense. Plant pathogens secrete effector proteins to manipulate defense signaling in their hosts. Evidence is emerging that some of these effectors target light signaling pathways. Several effectors from different kingdoms of life have converged on key chloroplast processes to take advantage of regulatory crosstalk. Moreover, plant pathogens also perceive and react to light in complex ways to regulate their own growth, development, and virulence. Recent work has shown that varying light wavelengths may provide a novel way of controlling or preventing disease outbreaks in plants.

Sigma factor binding protein 1 (CsSIB1) is a putative candidate of the major-effect QTL dm5.3 for downy mildew resistance in cucumber (Cucumis sativus)

The dm5.3 major-effect QTL in cucumber encodes a homolog of Arabidopsis sigma factor binding protein 1 (CsSIB1). CsSIB1 positively regulates defense responses against downy mildew in cucumber through the salicylic acid (SA) biosynthesis/signaling pathway. Downy mildew (DM) caused by the oomycete pathogen Pseudoperonospora cubensis is an important disease of cucumber and other cucurbits. Our knowledge on molecular mechanisms of DM resistance is still limited. In this study, we reported identification and functional characterization of the candidate gene for the major-effect QTL, dm5.3 for DM resistance originated from PI 197088. The dm5.3 QTL was Modelized through marker-assisted development of near isogenic lines (NILs). NIL-derived segregating populations were used for fine mapping which narrowed the dm5.3 locus down to a 144 kb region. Based on multiple lines of evidence, we show that CsSIB1 (CsGy5G027140) that encodes the VQ motif-containing sigma factor binding protein 1 as the most likely candidate for dm5.3. Local association analysis identified a haplotype consisting of 7 SNPs inside the coding and promoter region of CsSIB1 that was associated with DM resistance. Expression of CsSIB1 was up-regulated with P. cubensis infection. Transcriptome profiling of NILs in response to P. cubensis inoculation revealed key players and associated gene networks in which increased expression of CsSIB1 antagonistically promoted salicylic acid (SA) but suppressed jasmonic acid (JA) biosynthesis/signaling pathways. Our work provides novel insights into the function of CsSIB1/dm5.3 as a disease resistance (R) gene. The roles of sigma factor binding protein genes in pathogen defense in cucumber were also discussed.

Plant defense: ARR11 response regulator as a potential player in Arabidopsis

Plant growth and response to environmental cues are largely driven by hormones. Salicylic acid (SA)- and jasmonic acid (JA)-mediated defenses have been shown to be effective against different types of attackers. SA-mediated defense is mainly effective against biotrophic pathogens and phloem-feeding insects, whereas JA-mediated defense is effective against necrotrophic pathogens and tissue-damaging insects. Cytokinins (CKs) are classic growth hormones that have also emerged as plant immunity modulators. Evidence pointed out that CKs contribute to the defense responses mediated by SA and JA, acting as hormone modulators of the SA/JA signaling backbone. Recently, we identified in Arabidopsis a type-B response regulator 11 (ARR 11) involved in cytokinin-mediated responses as a novel regulator of the SA/JA cross-talk. Here we investigated plant fitness and resistance against the fungal necrotrophic pathogen Botrytis cinerea in Arabidopsis wild-type Col-8 and defective arr11 mutant following SA, JA, CK single or combined treatment. Our results demonstrated that the CK and SA/JA/CK combination has a positive outcome on plant fitness in both Arabidopsis Col-8 and arr11 mutant,. The triple hormone treatment is efficient in increasing resistance to B. cinerea in Col-8 and this effect is stronger in arr11 mutant. The results will provide not only new background knowledge, corroborating the role of ARR11 in plant-defense related processes, but also new potential opportunities for alternative ways of protecting plants from fungal diseases.