Molecular and genetic insights into secondary metabolic regulation underlying insect-pest resistance in legumes.

Insect pests pose a major threat to agricultural production, resulting in significant economic losses for countries. A high infestation of insects in any given area can severely reduce crop yield and quality. This review examines the existing resources for managing insect pests and highlights alternative eco-friendly techniques to enhance insect pest resistance in legumes. Recently, the application of plant secondary metabolites has gained popularity in controlling insect attacks. Plant secondary metabolites encompass a wide range of compounds such as alkaloids, flavonoids, and terpenoids, which are often synthesized through intricate biosynthetic pathways. Classical methods of metabolic engineering involve manipulating key enzymes and regulatory genes to enhance or redirect the production of secondary metabolites in plants. Additionally, the role of genetic approaches, such as quantitative trait loci mapping, genome-wide association (GWAS) mapping, and metabolome-based GWAS in insect pest management is discussed, also, the role of precision breeding, such as genome editing technologies and RNA interference for identifying pest resistance and manipulating the genome to develop insect-resistant cultivars are explored, highlighting the positive contribution of plant secondary metabolites engineering-based resistance against insect pests. It is suggested that by understanding the genes responsible for beneficial metabolite compositions, future research might hold immense potential to shed more light on the molecular regulation of secondary metabolite biosynthesis, leading to advancements in insect-resistant traits in crop plants. In the future, the utilization of metabolic engineering and biotechnological methods may serve as an alternative means of producing biologically active, economically valuable, and medically significant compounds found in plant secondary metabolites, thereby addressing the challenge of limited availability.

Satellitome Analysis and Transposable Elements Comparison in Geographically Distant Populations of Spodoptera frugiperda.

Spodoptera frugiperda (fall armyworm) is a member of the superfamily Noctuoidea that accounts for more than a third of all Lepidoptera and includes a considerable number of agricultural and forest pest species. Spodoptera frugiperda is a polyphagous species that is a significant agricultural pest worldwide, emphasizing its economic importance. Spodoptera frugiperda's genome size, assembly, phylogenetic classification, and transcriptome analysis have all been previously described. However, the different studies reported different compositions of repeated DNA sequences that occupied the whole assembled genome, and the Spodoptera frugiperda genome also lacks the comprehensive study of dynamic satellite DNA. We conducted a comparative analysis of repetitive DNA across geographically distant populations of Spodoptera frugiperda, particularly satellite DNA, using publicly accessible raw genome data from eight different geographical regions. Our results showed that most transposable elements (TEs) were commonly shared across all geographically distant samples, except for the Maverick and PIF/Harbinger elements, which have divergent repeat copies. The TEs age analysis revealed that most TEs families consist of young copies 1-15 million years old; however, PIF/Harbinger has some older/degenerated copies of 30-35 million years old. A total of seven satellite DNA families were discovered, accounting for approximately 0.65% of the entire genome of the Spodoptera frugiperda fall armyworm. The repeat profiling analysis of satellite DNA families revealed differential read depth coverage or copy numbers. The satellite DNA families range in size from the lowest 108 bp SfrSat06-108 families to the largest (1824 bp) SfrSat07-1824 family. We did not observe a statistically significant correlation between monomer length and K2P divergence, copy number, or abundance of each satellite family. Our findings suggest that the satellite DNA families identified in Spodoptera frugiperda account for a considerable proportion of the genome's repetitive fraction. The satellite DNA families' repeat profiling revealed a point mutation along the reference sequences. Limited TEs differentiation exists among geographically distant populations of Spodoptera frugiperda.

Comparative microbiome analysis of Diaphorina citri and its associated parasitoids Tamarixia radiata and Diaphorencyrtus aligarhensis reveals Wolbachia as a dominant endosymbiont.

Microbiome analysis in a host-parasitoid interaction network was conducted to compare the taxonomic composition of bacterial communities of Diaphornia citri, Tamarixia radiata, and Diaphorencyrtus aligarhensis. The comparative analysis revealed differences in the composition and diversity of the symbiont populations across the host and its associated parasitoids. Proteobacteria was the most dominant phylum, representing 67.80% of the total bacterial community, while Candidatus Profftella armature and Wolbachia were the dominant genera across the host and parasitoids. There were clear differences observed in alpha and beta diversity of microbiota through the host and its associated parasitoids. The function prediction of bacterial communities and Pearson correlation analysis showed that specific bacterial communities displayed positive correlations with the carbohydrate metabolism pathway. Furthermore, when symbiotic bacteria were eliminated using a broad-spectrum antibiotic, tetracycline hydrochloride, the parasitoids' median survival time and longevity were significantly reduced. We confirmed the physiological effects of symbiotic bacteria on the fitness of parasitoids and demonstrated the effect of antibiotics in decreasing the food intake and measurement of amino acids in the hemolymph. This study sheds light on basic information about the mutualism between parasitoids and bacteria, which may be a potential source for biocontrol strategies for citrus psyllid, especially D. citri.

Comparative transcriptome analysis of Tamarixia radiata (Hymenoptera: Eulophidae) reveals differentially expressed genes upon heat shock.

Temperature is a key parameter that affects insect population, abundance, and distribution in tropical and subtropical regions. Tamarixia radiata Waterson (Hymenoptera: Eulophidae) is a species-specific ectoparasitoid widely used as a biological control agent for the major citrus pest Diphornia citri Kuwayama (Hemiptera: Liviidea). To date, T. radiata response to high temperature at the molecular level still is unclear. In this study, we conducted a comparative analysis of the transcriptomes of T. radiata exposed at 25 °C and 38 °C for 15 min. A total of 51,072 unigenes were obtained, 22,413 annotated with a mean length of 1054 bp. Differential expression analysis showed that 502 genes were identified, including 476 genes significantly up-regulated and 26 genes down-regulated after heat stress exposure. The Gene Ontology analysis showed that most enriched DEGs are categorized into "cellular process", "metabolic process" and "DNA binding." In addition, "Lysosome," "Longevity regulating pathway-multiple species," and "starch and sucrose metabolism" were highly enriched in Kyoto Encyclopedia of Genes and Genomes pathways. Transcriptome analyses showed that heat stress significantly induced the transcription of the molecular chaperone, immune response, stress signaling transduction, and oxidation resistance, including highly expressed heat shock proteins, ATPases, and detoxifying enzymes. Furthermore, the expression patterns of thirteen genes including heat shock proteins (HSP), glutathione S-transferase (GST) and cytochrome P450 were consistent with the transcriptome results obtained through qRT-PCR. Together, our results provided a comprehensive study of the molecular response of T. radiata to heat stress and provides new insight for the future functional validation of heat resistance-related genes.

Temperature-Dependent Biological Control Effectiveness of Tamarixia radiata (Hymenoptera: Eulophidea) Under Laboratory Conditions.

The parasitism rate and host-feeding rate of Tamarixia radiata (Hymenoptera: Eulophidae), an ectoparasitoid of Diaphorina citri (Hemiptera: Liviidae), were evaluated at 20, 27.5, 30, and 35°C, at 70 ± 5% RH, and 14 h of photoperiod. The biological control efficacy of T. radiata was evaluated by linking the age-stage predation rate with the two-sex life table. The net host-feeding rate (C0) by T. radiata was 32.05, 54.40, 17.25, and 1.92 nymphs per female parasitoid at 20, 27.5, 30, and 35°C, respectively. The total net nymphs killing rate (Z0) was 103.02, 223.82, 72.95, and 6.60 nymphs per female parasitoid at 20, 27.5, 30, and 35°C, respectively. Noneffective parasitism rate was observed at 35°C because of high mortality at this temperature. Our results indicated that temperature had meaningful effects on parasitism and host-feeding rate parameters in the laboratory, and may affect biological control efficiency of the parasitoid in the field. The highest host-feeding rate and total biological control efficiency of T. radiata were recorded at 27.5°C. Most importantly, we found that host-feeding activity of the parasitoid is temperature-dependent, and changed across temperature regimes: the host-feeding rate increased as the temperature increased up to 30°C, started to decrease after this temperature and declined to its minimum level at 35°C. This information is valuable for developing biological control and integrated pest management techniques for Asian citrus psyllid management.

First Report of Cladosporium Blossom Blight Caused by Cladosporium cladosporioides on Calliandra haematocephala in China.

Calliandra haematocephala Hassk., commonly called red powder puff, is widely cultivated as an ornamental plant in Taiwan, Hainan, Guangdong and Fujian in China (CAS, 1988). The flowers are dark crimson with conspicuous stamens, which give them the appearance of powder-puffs. Blossom blight on C. haematocephala was first observed in early January 2019 on plants grown on the university campus as well as in parks in Fuzhou city, with nearly 80% of flowers on individual plants infected. At various locations in the city, disease incidence was 100%. Symptoms appeared as grayish green fungal growth on the stamens with the entire flower eventually turning black and covered with masses of fungal spores. Fifteen single spore isolates obtained from nine necrotic stamen samples were purified and cultured on Potato dextrose agar (PDA) plates at 24 ℃.The resultant fungal colonies were olivaceous-green to olivaceous-brown and had a velvet-like appearance. Conidiophores were smooth-walled, solitary, non-nodulose, and measuring 40 to 340 × 3 to 4 µm (n=50). Ramoconidia were cylindrical-oblong or slightly curved with 0 to 3 septa, and measuring 10 to 25 × 3 to 4 µm (n=50). Conidia were smooth-walled and prolifically produced in long chains. Terminal conidia were aseptate, subglobose, ovoid to limoniform, measuring 3 to 6 × 2 to 2.5 µm (n=50). Intercalary conidia were elliptical to limoniform or subcylindrical, aseptate, measuring 5 to 12 × 2.5 to 3 µm (n=50). On the basis of its morphology, the causal organism was identified as Cladosporium cladosporioides (Bensch et al. 2010). For molecular identification, pure cultures of five single-spore isolates were used for DNA extraction. A fragment in the ITS regions of the fungal rDNA, the ACT and the TEF1-α, was amplified using the primers ITS1/ITS4, ACT-512F/ACT-783R, and EF1728 F/EF1-986R. The DNA sequences obtained from all five isolates were identical. The resulting ITS (MK720012) and ACT (MN013164), and TEFl-α (MK752020) sequences from a representative isolate MRCIM19 were 98-100% identical to the C. cladosporioides accessions (ITS: MH863979, MG228421; ACT: HM148509, JF499878, HM148532; TEFl-α: JF499872). To test pathogenicity, a spore suspension (1×105 conidia/mL) was prepared from a seven- day- old culture of isolate MRCIM19 and 10 mL of the suspension was sprayed onto six flowers on each of three C. haematocephala plants. Sterile distilled water was sprayed onto three flowers of two plants as control. The inoculated flowers were covered with plastic bags which were removed two days post inoculation. Disease symptoms were recorded on each flower at 10 days post inoculation. Based on the morpho-molecular characters, the re-isolated fungus from the inoculated flowers was C. cladosporioides. This fungus was previously reported to cause blossom blight in strawberry in the USA and Korea (Gubler et al. 1999; Nam et al. 2015). Although it has been reported from many plants (Zhang 2003) in China, this is the first report of C. cladosporioides on C. haematocephala worldwide. References Bensch, K. et al. 2010. Stud Mycol. 67:1-94. Chinese Academy of Sciences (CAS), 1988. Flora Republicae Popularis Sinicae Editorial Committee, Beijing Sci. Press., 39: 38. Gubler, W. D. et al. 1999. Plant Dis. 83:400. Nam, M. H. et al. 2015. Microbiol. 43: 354-359. Zhang Z., Ed. 2003. Flora fungorum sinicorum, Vol. 14. Cladosporium, Fusicladium, Pyricularia. Beijing Science Press. 297.

Effects of Seedling Age on Colonization Patterns of Citrus limon Plants by Endophytic Beauveria bassiana and Metarhizium anisopliae and Their Influence on Seedlings Growth.

The inoculation methods, the fungal strains, and several other factors are known to influent the success of fungal entomopathogens colonization in plants. The physiological status of the plant could also be another determinant. In the present study, the ability of three strains of Beauveria bassiana and one strain of Metarhizium anisopliae to successfully colonize Citrus limon plants and the influence of seedling age on endophytic colonization success was examined. Three, 4, and 6 months old seedlings were inoculated with 10 mL of 1 × 108 conidial·mL-1 suspensions of each of the four fungal strains via foliar spraying. All fungal strains successfully colonized citrus seedlings and were sustained up to 2 months in colonized plants irrespective of the seedling age, with differences in the mean percentage colonization recorded at various post-inoculation periods among the fungal strains. The highest percent endophytic fungi recovery rate was recorded in the 3 months old seedlings, where fungal mycelia of inoculated fungi were successfully re-isolated from 65.6% of the untreated newly developed leaf and stem tissues. One strain of B. bassiana, BB Fafu-12, significantly improved seedling height and leaf number. The study demonstrates the influence of seedling age on B. bassiana and M. anisopliae successful colonization in the citrus plant.