Abstract
What makes an insect a pest of crops and how do new pest species may appear? /nWhile a global food crisis threatens, 20 % of crops are eaten by insects. Providing knowledge on insect pest genomes, and on the ability of insects to adapt to different host-plants and to diversify may help deciphering new crop plant protection strategies. /n /nSpeciation, adaptation and genomes, transcriptome, epigenome /nSpeciation is a gradual process through which two populations of the same species will accumulate genetic differences and lose the ability to cross. Adaptation to the environment, including the host-plant for herbivores, can lead to the formation of new species. /nOur insect model, the moth Spodoptera frugiperda, the “fall armyworm” is a pest of crops. It exist as two variants, one found on corn, the other found on rice or pasture grass. Both variants coexist in the same geographical areas and are morphologically indistinguishable. The primary goal of the project is to know whether they correspond to one or two species. /nWe want to know if they cross each other in the laboratory, but also in nature. On the other hand we want to know if they have accumulated genetic differences (mutations, rearrangements, differences in transposable elements). /nOur second goal is to identify genes involved in adaptation to the host plant and and to know how their expression is regulated on the two plants. In other words, we want to know if the two variants use the same genes when making their life cycle on one or the other of the two host plants or whether certain genes are turned on (expressed) on plants and off (not expressed) on the other. The ability of a living to turn on or off certain genes depending on its environment is what is called «the regulation of gene expression.« It involves modifications of proteins and DNA or proteins associated with DNA. We want to identify some of these changes. /nFinally we want to determine if the host plant had a role in the formation of two variants, or if they diverged before the arrival of rice and corn crops. /nThis project brings together the complementary skills of four laboratories, DGIMI for genomics of adaptation to the plant and its regulation, CBGP for phylogenetics and study of natural populations structure, INRIA Rennes for comparative genomes analysis, URGI, for comparative analysis of transposable elements. /n /nIntegration of different approaches to meet the goals /nPhysiology / genetics /nIn order to determineif the 2 variants are species or populations of the same species, we perform crosses of lab individuals. We measure the number of fertile couples. If an offspring is obtained, we check whether the larvae carry the genetic material of their parents in expected proportion. To see which genes are necessary for the insect to develop on one or the other host plants, we follow the development of the two variants on plants under controlled temperature, humidity, lighting conditions: We measure the weight of insect and their development time on the two plants. /nTranscriptomics /nThe genetic material is stored in the cell nuclei, as genes carried by the chromosomes. Copies of genes called mRNA contain a message that can be translated into proteins in the cytoplasm of cells. To know which genes are necessary for the insect to grow on one plant, mRNA will be extracted from larvae. By sequencing, the messages coded by these mRNA will be analyzed. We will then compare the messages expressed on different plants. /nGenomics /nWe will compare the whole genome sequence of the two insects, not only the genes, but the genomic region located between genes containing transposable elements. /nEpigenomics /nWe will look at the factors that regulate gene expression by chromatin immunoprecipitation experiments, which permit identification of marks that are transmitted from one cell generation to the next in addition to the genetic code of bases. /nPhylogenetic /nIt is from the comparison of gene sequences of individuals from natural populations to trace their genealogy and estimate their divergence times. /nphylogeographic / population genetics /nIt is to study the distribution of the two variants over a wide geographical area. At a more local level we try to see if variants cross each other in nature, looking if they exchange genes and they have alleles (forms of genes) in common by sequence analysis of some markers in individuals collected in the field.
France