Multiparental RNA-seq driven eQTL screening identifies loci underlying host plant fitness in a generalist herbivore

The two-spotted spider mite (Tetranychus urticae) is a highly adaptable pest, yet the genetic factors contributing to its ability to thrive on various host plants are not fully understood. A research team aimed to identify genetic loci associated with the mite's fitness when transitioning from a common host (bean) to a more challenging host (tomato).

Traditional QTL mapping methods struggle with complex genetic backgrounds and the high costs associated with trans-eQTL hotspot detection, making this study particularly noteworthy.

To overcome these challenges, the researchers employed a multiparental mapping strategy using RNA-seq. A randomly mating population was generated on bean from a limited number of genetically diverse, often heterozygous parents. This population was then transferred to tomato prior to RNA-seq. By sequencing the genomes of the parents and the mapping population individuals, the team was able to reconstruct the genomes as combinations of parental haploblocks.

This innovative approach enabled the identification of 23 distinct trans-eQTL hotspot regions associated with the expression of numerous target genes.

The most significant hotspot was located on chromosome 3 and was associated with the expression of approximately 900 genes. This region showed enrichment for functions related to detoxification and digestion, suggesting a potential role in the mite's adaptation to the new host plant. Furthermore, the study found that four specific genotypes within these trans-eQTL hotspot regions explained significant variation in the mite's fitness on the challenging tomato host.

This finding contrasts with traditional QTL mapping approaches, where such genotypes would not have been detected due to multiple testing corrections.

Overall, this study demonstrates the power of a multiparental RNA-seq driven eQTL screening strategy for identifying trans-eQTL hotspots and discovering trait-associated loci in complex genetic backgrounds. This approach has the potential to greatly enhance our understanding of the genetic basis of host plant fitness in multiparental genetic systems.