Molecular Characterization and Pathogenicity of a Novel Soybean-Infecting Monopartite Geminivirus in China

Elucidating the ecophysiology of soybean pod-sucking stinkbug Riptortus pedestris (Hemiptera: Alydidae) based on de novo genome assembly and transcriptome analysis

Food security is important for the ever-growing global population. Soybean, Glycine max (L.) Merr., is cultivated worldwide providing a key source of food, protein and oil. Hence, it is imperative to maintain or to increase its yield under different conditions including challenges caused by abiotic and biotic stresses. In recent years, the soybean pod-sucking stinkbug Riptortus pedestris has emerged as an important agricultural insect pest in East, South and Southeast Asia. Here, we present a genomics resource for R. pedestris including its genome assembly, messenger RNA (mRNA) and microRNA (miRNA) transcriptomes at different developmental stages and from different organs. As insect hormone biosynthesis genes (genes involved in metamorphosis) and their regulators such as miRNAs are potential targets for pest control, we analyzed the sesquiterpenoid (juvenile) and ecdysteroid (molting) hormone biosynthesis pathway genes including their miRNAs and relevant neuropeptides. Temporal gene expression changes of these insect hormone biosynthesis pathways were observed at different developmental stages. Similarly, a diet-specific response in gene expression was also observed in both head and salivary glands. Furthermore, we observed that microRNAs (bantam, miR-14, miR-316, and miR-263) of R. pedestris fed with different types of soybeans were differentially expressed in the salivary glands indicating a diet-specific response. Interestingly, the opposite arms of miR-281 (-5p and -3p), a miRNA involved in regulating development, were predicted to target Hmgs genes of R. pedestris and soybean, respectively. These observations among others highlight stinkbug's responses as a function of its interaction with soybean. In brief, the results of this study not only present salient findings that could be of potential use in pest management and mitigation but also provide an invaluable resource for R. pedestris as an insect model to facilitate studies on plant-pest interactions.

Molecular identification and development of an infectious cDNA clone of Trichosanthes kirilowii-infecting cucurbit mild mosaic virus

Trichosanthes kirilowii has been mainly grown for use in traditional Chinese medicine. In this study, cucurbit mild mosaic virus (CuMMV) belonging to the genus Fabavirus was identified from T. kirilowii plants. CuMMV possesses a segmented, bipartite linear single-stranded RNA genome composed of RNA1 and RNA2. Sequence analysis showed that each genomic segment shares the highest sequence similarity with those of CuMMV isolated from pumpkin. A full-length infectious cDNA clone of CuMMV was further constructed and was found to induce typical symptoms in T. kirilowii, Cucumis sativus, C. melo, Citrullus lanatus, and Cucurbita pepo. The sap inoculum derived from the infectious cDNA clone of CuMMV could be mechanically transmitted and reproduce similar symptoms in the tested plants. This is the first report on the construction of a biologically active, full-length infectious cDNA clone of CuMMV, which will provide a useful tool in understanding CuMMV-encoded proteins and plant-CuMMV interactions.

The rising threat of geminiviruses: molecular insights into the disease mechanism and mitigation strategies

BACKGROUND

Geminiviruses are among the most threatening emerging plant viruses, accountable for a huge loss to agricultural production worldwide. These viruses have been responsible for some serious outbreaks during the last few decades across different parts of the world. Sincere efforts have been made to regulate the disease incidence by incorporating a multi-dimensional approach, and this process has been facilitated greatly by the advent of molecular techniques. But, the mixed infection due to the polyphagous nature of vectors results in viral recombination followed by the emergence of novel viral strains which thus renders the existing mitigation strategies ineffective. Hence, a multifaceted insight into the molecular mechanism of the disease is really needed to understand the regulatory points; much has been done in this direction during the last few years. The present review aims to explore all the latest developments made so far and to organize the information in a comprehensive manner so that some novel hypotheses for controlling the disease may be generated.

METHODS AND RESULTS

Starting with the background information, diverse genera of geminiviruses are listed along with their pathological and economic impacts. A comprehensive and detailed mechanism of infection is elaborated to study the interactions between vector, host, and virus at different stages in the life cycle of geminiviruses. Finally, an effort isalso made to analyze the progress made at the molecular level for the development of various mitigation strategies and suggest more effective and better approaches for controlling the disease.

CONCLUSION

The study has provided a thorough understanding of molecular mechanism of geminivirus infection.

Whole-plant microbiome profiling reveals a novel geminivirus associated with soybean stay-green disease

Microbiota colonize every accessible plant tissue and play fundamental roles in plant growth and health. Soybean stay-green syndrome (SGS), a condition that causes delayed leaf senescence (stay-green), flat pods and abnormal seeds of soybean, has become the most serious disease of soybean in China. However, the direct cause of SGS is highly debated, and little is known about how SGS affect soybean microbiome dynamics, particularly the seed microbiome. We studied the bacterial, fungal, and viral communities associated with different soybean tissues with and without SGS using a multi-omics approach, and investigated the possible pathogenic agents associated with SGS and how SGS affects the assembly and functions of plant-associated microbiomes. We obtained a comprehensive view of the composition, function, loads, diversity, and dynamics of soybean microbiomes in the rhizosphere, root, stem, leaf, pod, and seed compartments, and discovered that soybean SGS was associated with dramatically increased microbial loads and dysbiosis of the bacterial microbiota in seeds. Furthermore, we identified a novel geminivirus that was strongly associated with soybean SGS, regardless of plant cultivar, sampling location, or harvest year. This whole-plant microbiome profiling of soybean provides the first demonstration of geminivirus infection associated with microbiota dysbiosis, which might represent a general microbiological symptom of plant diseases.