Zhen-Zhen Wei

Spodoptera frugiperda poses a severe threat to crops, causing substantial economic losses. The increased use of chemical pesticides has led to resistance in S. frugiperda populations. Micro ribonucleic acids (MicroRNAs or miRNAs) are pivotal in insect growth and development. This study aims to identify miRNAs across different developmental stages of S. frugiperda to explore differential expression and predict target gene functions. High-throughput sequencing of miRNAs was conducted on eggs, 3rd instar larvae, pupae, and adults. Bioinformatics analyses identified differentially expressed miRNAs specifically in larvae, with candidate miRNAs screened to predict target genes, particularly those involved in detoxification pathways. A total of 184 known miRNAs and 209 novel miRNAs were identified across stages. Comparative analysis revealed 54, 15, and 18 miRNAs differentially expressed in larvae, compared to egg, pupa, and adult stages, respectively. Eight miRNAs showed significant differential expression across stages, validated by quantitative reverse transcription PCR (qRT-PCR). Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses predicted target genes’ functions, identifying eight differentially expressed miRNAs targeting 10 gene families associated with detoxification metabolism, including P450s, glutathione S-transferase (GSTs), ATP-binding cassette (ABC) transporters, and sodium channels. These findings elucidate the species-specific miRNA profiles and regulatory mechanisms of detoxification-related genes in S. frugiperda larvae, offering insights and strategies for effectively managing this pest.

Humulus scandens, (Lour.) Merr., is a climbing herb which are used as traditional Chinese medicine, a raw material for papermaking, making soap, and replacing hops H. lupulus. This herb is distributed in many provinces of China, including Sichuan province. During March and June 2022, powdery mildew was found on leaves of H. scandens in the modern agricultural high-tech demonstration garden of Sichuan Academy of Agricultural Science, Chengdu, Sichuan Province, China. Abundant white or grayish powdery colonies could be seen on the surface of leaves, and 30%-100% of leaf areas were affected. Some of the infected leaves were either chlorotic or senescent. About 90% of the observed plants showed powdery mildew symptoms. Conidiophores (n = 25) were 74.0 to 160.1 μm × 8.7 to 12.7 μm (on average 120.9 × 10.4 μm) and composed of cylindrical foot cells (length 31.9-72.9 μm, average 50.1 µm) and conidia (mostly 10 conidia) in chains. Barrel-shaped conidia with fibrosin bodies (n = 30) were 12.8 to 21.0 μm × 7.9 to 15 μm, on average 16.7 × 11.3 μm, with a length/width ratio of 1.5. Chasmothecia were not found. Based on these morphologic characteristics, the pathogen was initially identified as Podosphaera macularis (Braun and Cook 2012; Mahaffee et al. 2009). To confirm the identification, two isolates (PDLC0315 and PDLC0412) of P. macularis mycelia and conidia were collected, and mycelia and conidia were combined for a single DNA extraction from each isolate. With the total genomic DNA, the sequences of the internal transcribed spacer (ITS), 5.8S rRNA, the 18S and 28S large subunit ribosomal DNA (LSU) (Bradshaw and Tobin 2020; White et al. 1990), were bi-directionally sequenced and deposited in GenBank (ON862625.1 and ON862630.1). The ON862625.1 and ON862630.1 showed 100% similarity with sequences of P. macularis isolate CT1 (MH687414.1). Phylogenetic analyses based on the combined ITS and 28S rDNA sequences indicated that the two specimens, PDLC0315 and PDLC0412 formed a monophyletic clade together with sequences retrieved from Podosphaera macularis CT1 and Head quarter 31 (KX842348.1). The pathogenicity test with the fungus was confirmed by gently pressing the infected leaves onto three healthy wild plants from the same geographical location. Three uninoculated wild plants served as controls. Six inoculated and non-inoculated plants were placed in different growth chambers with a 16-h photoperiod at 22±2°C and 70% of relative humidity. After 10 to 14 days, powdery mildew colonies developed on inoculated plants. Non-inoculated control plants did not show any symptoms. The fungus on inoculated leaves was morphologically identical to that first observed in the garden. As far as we know, this study is the first report of powdery mildew disease in Humulus scandens caused by Podosphaera macularis in China. Rapid expansion and wild distribution of H. scandens could lead to increased powdery mildew risk in outdoor cultivation. Due to the invasive potential of the powdery mildew fungi, this record is important in the context of the range extension of Podosphaera macularis.

Reactive oxygen species (ROS)- and hypersensitive response (HR)-mediated cell death have long been known to play critical roles in plant immunity to pathogens. Wheat powdery mildew caused by Blumeria graminis f. sp. tritici ( Bgt) is a destructive wheat pathogen. Here, we report a quantitative analysis of the proportion of infected cells with local apoplastic ROS (apoROS) versus intracellular ROS (intraROS) accumulation in various wheat accessions that carry different disease resistance genes ( R genes) at a series of time points postinfection. The proportion of apoROS accumulation was 70 to 80% of the infected wheat cells detected in both compatible and incompatible host−pathogen interactions. However, intensive intraROS accumulation followed by localized cell death responses was detected in 11 to 15% of the infected wheat cells, mainly in wheat lines that carried nucleotide-binding leucine-rich repeat R genes (e.g., Pm3F, Pm41, TdPm60, MIIW72, and Pm69). The lines that carry unconventional R genes, Pm24 ( Wheat Tandem Kinase 3) and pm42 (a recessive R gene), showed fewer intraROS responses, whereas 11% of Pm24 line-infected epidermis cells still showed HR cell death, suggesting that different resistance pathways are activated there. Here, we also demonstrated that ROS could not act as a strong systemic signal for inducing high resistance to Bgt in wheat, although it induced the expression of pathogenesis-related genes. These results provide new insights into the contribution of intraROS and localized cell death to immune responses against wheat powdery mildew.

Wheat powdery mildew (Blumeria graminis f. sp. tritici, Bgt, recently clarified as B. graminis s. str.), is one of the most destructive diseases of wheat. Pm60 is a nucleotide-binding leucine-rich repeat (NLR) gene that confers race-specific resistance to Bgt. Allelic variants (Pm60, Pm60a, and Pm60b) were found in Triticum urartu and T. dicoccoides, the wild progenitors of wheat. In the present study, we studied the diversity of the Pm60 locus in a large set of wheat germplasm and found 20 tetraploid wheats harboring the Pm60 alleles, which correspond to three novel haplotypes (HapI–HapIII). HapI (Pm60 allele) and HapII (Pm60a allele) were present in domesticated tetraploid wheats, whereas HapIII (Pm60a allele) was identified in wild tetraploid T. araraticum. A sequence comparison of HapII and HapIII revealed that they differed by three SNPs and a GCC deletion. Results of the phylogenetic analysis revealed that HapII was more closely related to the functional haplotype MlIW172. Infection tests showed that HapII-carrying lines display a partial resistance response to Bgt#GH, while HapI was susceptible. Our results provide insights into the genetic evolution of the Pm60 locus and potential valuable alleles for powdery mildew resistance breeding.

The destructive wheat powdery mildew disease is caused by the fungal pathogen Blumeria graminis f. sp. tritici (Bgt). PmG3M, derived from wild emmer wheat Triticum dicoccoides accession G305-3M, is a major gene providing a wide-spectrum resistance against Bgt. PmG3M was previously mapped to wheat chromosome 6B using an F₆ recombinant inbred line (RIL) mapping population generated by crossing G305-3M with the susceptible T. durum wheat cultivar Langdon (LDN). In the current study, we aimed to explore the defense mechanisms conferred by PmG3M against Bgt. Histopathology of fungal development was characterized in artificially inoculated leaves of G305-3M, LDN, and homozygous RILs using fluorescence and light microscopy. G305-3M exhibited H₂O₂ accumulation typical of a hypersensitive response, which resulted in programmed cell death (PCD) in Bgt-penetrated epidermal cells, while LDN showed well-developed colonies without PCD. In addition, we observed a post-haustorial resistance mechanism that arrested the development of fungal feeding structures and pathogen growth in both G305-3M and resistant RIL, while LDN and a susceptible RIL displayed fully developed digitated haustoria and massive accumulation of fungal biomass. In contrast, both G305-3M and LDN exhibited callose deposition in attempt to prevent fungal invasion, supporting this as a mechanism of a basal defense response not associated with PmG3M resistance mechanism per se. The presented results shed light on the resistance mechanisms conferred by PmG3M against wheat powdery mildew.

Phytohormones are key regulators of plant growth, development, and signalling networks involved in responses to diverse biotic and abiotic stresses. Transcriptional reference maps of hormone responses have been reported for several model plant species such as Arabidopsis thaliana, Oryza sativa, and Brachypodium distachyon. However, because of species differences and the complexity of the wheat genome, these transcriptome data are not appropriate reference material for wheat studies. We comprehensively analysed the transcriptomic responses in wheat spikes to seven phytohormones, including indole acetic acid (IAA), gibberellic acid (GA), abscisic acid (ABA), ethylene (ET), cytokinin (CK), salicylic acid (SA), and methyl jasmonic acid (MeJA). A total of 3386 genes were differentially expressed at 24 h after the hormone treatments. Furthermore, 22.7% of these genes exhibited overlapping transcriptional responses for at least two hormones, implying there is crosstalk among phytohormones. We subsequently identified genes with expression levels that were significantly and differentially induced by a specific phytohormone (i.e., hormone-specific responses). The data for these hormone-responsive genes were then compared with the transcriptome data for wheat spikes exposed to biotic (Fusarium head blight) and abiotic (water deficit) stresses. Our data were used to develop a transcriptional reference map of hormone responses in wheat spikes.