CsWRKY25 Improves Resistance of Citrus Fruit to Penicillium digitatum via Modulating Reactive Oxygen Species Production

The CmTGA1-CmRbohD Cascade Confers Resistance Against Chrysanthemum White Rust by Promoting Reactive Oxygen Species Generation

Chrysanthemum white rust (CWR), caused by Puccinia horiana Heen., is a serious disease of chrysanthemum worldwide. This disease reduces the quality and yield of Chrysanthemum morifolium, leading to significant losses for chrysanthemum growers and industries. It is often referred to as the 'cancer' of chrysanthemum. The most effective approach to managing CWR is to utilise host resistance. Reactive oxygen species (ROS) are conserved basic defence compounds in higher plants that are generated in response to biotic stresses. This study reported the TGACG-binding (TGA) transcription factor 1 (CmTGA1) in chrysanthemum. Subcellular localisation analysis revealed that CmTGA1 is localised in the nucleus and cytoplasm. Overexpression or knockout of CmTGA1 in chrysanthemum increased or reduced CWR resistance by regulating ROS generation, the activities of antioxidant enzymes, and CmRbohD (a gene mediating ROS generation) expression. Yeast one-hybrid, dual-luciferase, and electrophoretic mobility shift assays showed that CmTGA1 bound directly to the as-1 element in the promoter region of CmRbohD. Subcellular localisation analysis revealed that CmRbohD was localised in the cytomembrane and cytoplasm. CmRbohD was induced by P. horiana infection and enhanced CWR resistance by promoting ROS generation, activating the antioxidant enzyme system, and catalysing lignin biosynthesis. Our results showed that CmTGA1 activated CmRbohD to improve the CWR resistance via the ROS pathway in chrysanthemum. Our findings provided novel insights into the regulatory pathways involving the CmTGA1-CmRbohD cascade-mediated regulation of CWR resistance, demonstrating an effective strategy to improve tolerance to P. horiana in chrysanthemum.

CaWRKY20 Negatively Regulates Plant Resistance to Colletotrichum scovillei in Pepper

Chili anthracnose, a fungal disease caused by Colletotrichum scovillei, is among the most devastating diseases affecting pepper (Capsicum annuum L.). Although WRKY transcription factors play important roles in plant immunity, it is unknown how WRKY gene family members contribute to pepper plant resistance to C. scovillei. Here, CaWRKY20 was found to negatively regulate pepper resistance to C. scovillei, which was demonstrated by virus-induced gene silencing and transient overexpression in pepper. Moreover, overexpression of CaWRKY20 enhanced susceptibility to C. scovillei in tomato. Additionally, our findings demonstrated that CaWRKY20 can indirectly regulate the expression of salicylic acid (SA)-related defense genes (CaPR1, CaPR10 and CaSAR8.2) as well as reactive oxygen species (ROS)-scavenging enzyme genes (CaCAT, CaPOD and CaSOD) in response to C. scovillei. In addition, CaWRKY20 was found to interact with CaMIEL1 in the nucleus to regulate the defense response to C. scovillei in pepper. Furthermore, CaWRKY20 directly bound to the W-box in the promoter of SYSTEMIC ACQUIRED RESISTANCE DEFICIENT 1 (CaSARD1) and suppressed its expression, resulting in reduced resistance to C. scovillei. These results will clarify the mechanism by which WRKY transcription factors are involved in pepper disease resistance and can thus facilitate molecular breeding for anthracnose-resistant varieties.

Recent advances in functional assays of WRKY transcription factors in plant immunity against pathogens

WRKY transcription factors (TFs) are one of the largest transcription factor families in plants and play important roles in plant processes, most notably in responding to diverse biotic and abiotic stresses. This article reviews the recent research progresses on WRKY TFs in regulating plant immunity, which includes both positive and negative regulation. WRKY TFs were shown to regulate plant defense against pathogens including fungi, bacteria, oomycetes, and viruses by modulating downstream pathogen resistance genes or interacting with other regulators. Plant signaling pathways or components involved in the regulatory network of WRKY-mediated plant immunity mainly involve the action of phytohormones, MAPKs (Mitogen-activated protein kinases), and other transcription factors. The interaction of WRKY TFs with these factors during pathogen resistance was discussed in this article, which may contribute to understanding the mechanisms of WRKY transcription factors in plant immunity.

Functional characterisation of WRKY transcription factor CrWRKY48 involved in regulating seed abortion of Ponkan (Citrus reticulata)

Citrus fruits are one of the most important fruits in the world, and their seedless character is favored by consumers. WRKY is a plant-specific transcription factor family involved in all aspects of plant growth and development. However, the molecular mechanism of seedless fruit formation in citrus and the role of the WRKY gene family in seed abortion are still poorly understood. In this study, we identified 47 WRKY family genes in the citrus fruit Citrus reticulata and comprehensively characterized the WRKY gene family through gene structure and evolutionary relationships. The expression patterns and protein interaction networks of the WRKY gene family were analyzed based on citrus seed abortion transcriptome data, and several WRKY genes that may be involved in the seed abortion regulation were excavated. Furthermore, CrWRKY48 was verified to regulate seed abortion positively in Arabidopsis thaliana, and the rate of seed abortion caused by overexpression of CrWRKY48 reached 45.48%. Using terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling assays, DNA affinity purification sequencing and yeast-one-hybrid assays, we found that CrWRKY48 activated excessive programmed cell death by regulating the expression of programmed cell death-related genes such as SOBIR1. Our results show the potential regulation of the WRKY gene family for citrus seed abortion and provide novel insights into the role of CrWRKY48 in mediating citrus seed abortion by activating programmed cell death.

Genome-wide identification and data mining reveals major-latex protein (MLP) from the PR-10 protein family played defense-related roles against phytopathogenic challenges in cassava (Manihot esculenta Crantz)

Despite being identified in previous articles, the pathogenesis-related 10 (PR-10) protein remains relatively overlooked and has yet to be fully characterized in numerous plant species. This research employs a comprehensive data mining approach to in silico characterize PR-10 proteins in cassava, a vital crop plant globally. In this study, the focus was on in silico identified 53 cassava PR-10 proteins, which can be categorized into two main subgroups: 34 major latex proteins (MLPs) and 13 major allergen proteins, Pru ar 1, based on their phylogenetic relationship. The genome collinearity analysis with the rubber tree showed a possible evolutionary relationship of the PR-10 gene between these two Euphorbiaceae species, specifically on their chromosome 15. Notably, MLP423 and other MLP proteins were identified in various previously published cassava transcriptome datasets in response to biotic treatments from diverse phytopathogens, including anthracnose fungus, viruses, and bacterial blight. Ligand prediction and molecular docking of three MLP423 proteins have revealed potential interaction with cytokinin and abscisic acid hormones. Their expressions and predicted binding affinities are discussed here, highlighting their role as contributors to cassava's defense network against key diseases.

A Calcium-Dependent Protein Kinase Regulates the Defense Response in Citrus sinensis

Citrus Huanglongbing (HLB), which is caused by 'Candidatus Liberibacter asiaticus' (CLas), is one of the most destructive citrus diseases worldwide, and defense-related Citrus sinensis gene resources remain largely unexplored. Calcium signaling plays an important role in diverse biological processes. In plants, a few calcium-dependent protein kinases (CDPKs/CPKs) have been shown to contribute to defense against pathogenic microbes. The genome of C. sinensis encodes dozens of CPKs. In this study, the role of C. sinensis calcium-dependent protein kinases (CsCPKs) in C. sinensis defense was investigated. Silencing of CsCPK6 compromised the induction of defense-related genes in C. sinensis. Expression of a constitutively active form of CsCPK6 (CsCPK6CA) triggered the activation of defense-related genes in C. sinensis. Complementation of CsCPK6 rescued the defense-related gene induction in an Arabidopsis thaliana cpk4/11 mutant, indicating that CsCPK6 carries CPK activity and is capable of functioning as a CPK in Arabidopsis. Moreover, an effector derived from CLas inhibits defense induced by the expression of CsCPK6CA and autophosphorylation of CsCPK6, which suggests the involvement of CsCPK6 and calcium signaling in defense. These results support a positive role for CsCPK6 in C. sinensis defense against CLas, and the autoinhibitory regulation of CsCPK6 provides a potential genome-editing target for improving C. sinensis defense. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Overexpression of CmWRKY8-1-VP64 Fusion Protein Reduces Resistance in Response to Fusarium oxysporum by Modulating the Salicylic Acid Signaling Pathway in Chrysanthemum morifolium

Chrysanthemum Fusarium wilt, caused by the pathogenic fungus Fusarium oxysporum, severely reduces ornamental quality and yields. WRKY transcription factors are extensively involved in regulating disease resistance pathways in a variety of plants; however, it is unclear how members of this family regulate the defense against Fusarium wilt in chrysanthemums. In this study, we characterized the WRKY family gene CmWRKY8-1 from the chrysanthemum cultivar 'Jinba', which is localized to the nucleus and has no transcriptional activity. We obtained CmWRKY8-1 transgenic chrysanthemum lines overexpressing the CmWRKY8-1-VP64 fusion protein that showed less resistance to F. oxysporum. Compared to Wild Type (WT) lines, CmWRKY8-1 transgenic lines had lower endogenous salicylic acid (SA) content and expressed levels of SA-related genes. RNA-Seq analysis of the WT and CmWRKY8-1-VP64 transgenic lines revealed some differentially expressed genes (DEGs) involved in the SA signaling pathway, such as PAL, AIM1, NPR1, and EDS1. Based on Gene Ontology (GO) enrichment analysis, the SA-associated pathways were enriched. Our results showed that CmWRKY8-1-VP64 transgenic lines reduced the resistance to F. oxysporum by regulating the expression of genes related to the SA signaling pathway. This study demonstrated the role of CmWRKY8-1 in response to F. oxysporum, which provides a basis for revealing the molecular regulatory mechanism of the WRKY response to F. oxysporum infestation in chrysanthemum.

Comparative transcriptomic and metabolomic analyses reveal the delaying effect of naringin on postharvest decay in citrus fruit

INTRODUCTION

Naringin exhibits antioxidant capacity and can partially inhibit pathogens in many horticultural products, such as citrus fruit; however, the effects of naringin on the storage quality and mechanisms that regulate senescence in citrus fruit have not been comprehensively analyzed.

METHODS AND RESULTS

In this study, exogenous naringin treatment was found to significantly delay citrus fruit disease, decreasing the H₂O₂ content, increasing the antioxidant capacity and maintaining the quality of the fruit. Metabolomic analysis of citrus peel indicated the vast majority (325) of metabolites belonging to flavonoids. Moreover, the auraptene, butin, naringenin, and luteolin derivative levels within the phenylpropanoid pathway were significantly higher in the naringin-treated fruit than in the control fruit. Transcriptomic analysis also revealed that twelve genes in the phenylpropanoid and flavonoid biosynthesis pathways were significantly upregulated. Further analysis with a co-expression network revealed significant correlation between these differential genes and metabolites. Additionally, MYC and WRKY, screened from the MAPK signaling pathway, may contribute to naringin-induced disease resistance.

CONCLUSION

In conclusion, naringin treatment can efficiently delay decay and maintain the quality of citrus fruit, mainly by promoting metabolites accumulation, and upregulating differentially expressed genes in phenylpropanoid and flavonoid biosynthesis pathway. This study provides a better understanding of the regulatory mechanisms through which naringin delays citrus fruit decay and maintains fruit quality.

Genome-wide identification of Cymbidium sinense WRKY gene family and the importance of its Group III members in response to abiotic stress

Transcription factors (TFs) of the WRKY family play pivotal roles in defense responses and secondary metabolism of plants. Although WRKY TFs are well documented in numerous plant species, no study has performed a genome-wide investigation of the WRKY gene family in Cymbidium sinense. In the present work, we found 64 C. sinense WRKY (CsWRKY) TFs, and they were further divided into eight subgroups. Chromosomal distribution of CsWRKYs revealed that the majority of these genes were localized on 16 chromosomes, especially on Chromosome 2. Syntenic analysis implied that 13 (20.31%) genes were derived from segmental duplication events, and 17 orthologous gene pairs were identified between Arabidopsis thaliana WRKY (AtWRKY) and CsWRKY genes. Moreover, 55 of the 64 CsWRKYs were detectable in different plant tissues in response to exposure to plant hormones. Among them, Group III members were strongly induced in response to various hormone treatments, indicating their potential essential roles in hormone signaling. We subsequently analyzed the function of CsWRKY18 in Group III. The CsWRKY18 was localized in the nucleus. The constitutive expression of CsWRKY18 in Arabidopsis led to enhanced sensitivity to ABA-mediated seed germination and root growth and elevated plant tolerance to abiotic stress within the ABA-dependent pathway. Overall, our study represented the first genome-wide characterization and functional analysis of WRKY TFs in C. sinense, which could provide useful clues about the evolution and functional description of CsWRKY genes.