April 21, 2020  |  

Insect genomes: progress and challenges.

In the wake of constant improvements in sequencing technologies, numerous insect genomes have been sequenced. Currently, 1219 insect genome-sequencing projects have been registered with the National Center for Biotechnology Information, including 401 that have genome assemblies and 155 with an official gene set of annotated protein-coding genes. Comparative genomics analysis showed that the expansion or contraction of gene families was associated with well-studied physiological traits such as immune system, metabolic detoxification, parasitism and polyphagy in insects. Here, we summarize the progress of insect genome sequencing, with an emphasis on how this impacts research on pest control. We begin with a brief introduction to the basic concepts of genome assembly, annotation and metrics for evaluating the quality of draft assemblies. We then provide an overview of genome information for numerous insect species, highlighting examples from prominent model organisms, agricultural pests and disease vectors. We also introduce the major insect genome databases. The increasing availability of insect genomic resources is beneficial for developing alternative pest control methods. However, many opportunities remain for developing data-mining tools that make maximal use of the available insect genome resources. Although rapid progress has been achieved, many challenges remain in the field of insect genomics. © 2019 The Royal Entomological Society.

April 21, 2020  |  

Mitochondrial DNA and their nuclear copies in the parasitic wasp Pteromalus puparum: A comparative analysis in Chalcidoidea.

Chalcidoidea (chalcidoid wasps) are an abundant and megadiverse insect group with both ecological and economical importance. Here we report a complete mitochondrial genome in Chalcidoidea from Pteromalus puparum (Pteromalidae). Eight tandem repeats followed by 6 reversed repeats were detected in its 3308?bp control region. This long and complex control region may explain failures of amplifying and sequencing of complete mitochondrial genomes in some chalcidoids. In addition to 37 typical mitochondrial genes, an extra identical isoleucine tRNA (trnI) was detected at the opposite end of the control region. This recent mitochondrial gene duplication indicates that gene arrangements in chalcidoids are ongoing. A comparison among available chalcidoid mitochondrial genomes reveals rapid gene order rearrangements overall and high protein substitution rates in most chalcidoid taxa. In addition, we identified 24 nuclear sequences of mitochondrial origin (NUMTs) in P. puparum, summing up to 9989?bp, with 3617?bp of these NUMTs originating from mitochondrial coding regions. NUMTs abundance in P. puparum is only one-twelfth of that in its relative, Nasonia vitripennis. Based on phylogenetic analysis, we provide evidence that a faster nuclear degradation rate contributes to the reduced NUMT numbers in P. puparum. Overall, our study shows unusually high rates of mitochondrial evolution and considerable variation in NUMT accumulation in Chalcidoidea. Copyright © 2018. Published by Elsevier B.V.

April 21, 2020  |  

A Pathovar of Xanthomonas oryzae Infecting Wild Grasses Provides Insight Into the Evolution of Pathogenicity in Rice Agroecosystems

Xanthomonas oryzae (Xo) are critical rice pathogens. Virulent lineages from Africa and Asia and less virulent strains from the US have been well characterized. X. campestris pv. leersiae (Xcl), first described in 1957, causes bacterial streak on the perennial grass, Leersia hexandra, and is a close relative of Xo. L. hexandra, a member of the Poaceae, is highly similar to rice phylogenetically, is globally ubiquitous around rice paddies, and is a reservoir of pathogenic Xo. We used long read, single molecule, real time (SMRT) genome sequences of five strains of Xcl from Burkina Faso, China, Mali and Uganda to determine the genetic relatedness of this organism with Xo. Novel Transcription Activator-Like Effectors (TALEs) were discovered in all five strains of Xcl. Predicted TALE target sequences were identified in the L. perrieri genome and compared to rice susceptibility gene homologs. Pathogenicity screening on L. hexandra and diverse rice cultivars confirmed that Xcl are able to colonize rice and produce weak but not progressive symptoms. Overall, based on average nucleotide identity, type III effector repertoires and disease phenotype, we propose to rename Xcl to X. oryzae pv. leersiae (Xol) and use this parallel system to improve understanding of the evolution of bacterial pathogenicity in rice agroecosystems.

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