Genome analysis of Phrixothrix hirtus (Phengodidae) railroad worm shows the expansion of odorant-binding gene families and positive selection on morphogenesis and sex determination genes.

Among bioluminescent beetles of the Elateroidea superfamily, Phengodidae is the third largest family, with 244 bioluminescent species distributed only in the Americas, but is still the least studied from the phylogenetic and evolutionary points of view. The railroad worm Phrixothrix hirtus is an essential biological model and symbolic species due to its bicolor bioluminescence, being the only organism that produces true red light among bioluminescent terrestrial species. Here, we performed partial genome assembly of P. hirtus, combining short and long reads generated with Illumina sequencing, providing the first source of genomic information and a framework for comparative analyses of the bioluminescent system in Elateroidea. This is the largest genome described in the Elateroidea superfamily, with an estimated size of ∼3.4 Gb, displaying 32 % GC content, and 67 % transposable elements. Comparative genomic analyses showed a positive selection of genes and gene family expansion events of growth and morphogenesis gene products, which could be associated with the atypical anatomical development and morphogenesis found in paedomorphic females and underdeveloped males. We also observed gene family expansion among distinct odorant-binding receptors, which could be associated with the pheromone communication system typical of these beetles, and retrotransposable elements. Common genes putatively regulating bioluminescence production and control, including two luciferase genes corresponding to lateral lanterns green-emitting and head lanterns red-emitting luciferases with 7 exons and 6 introns, and genes potentially involved in luciferin biosynthesis were found, indicating that there are no clear differences about the presence or absence of gene families associated with bioluminescence in Elateroidea.

Cross-genera SSR transferability in cacti revealed by a case study using Cereus (Cereeae, Cactaceae).

The study of transferability of simple sequence repeats (SSR) among closely related species is a well-known strategy in population genetics, however transferability among distinct genera is less common. We tested cross-genera SSR amplification in the family Cactaceae using a total of 20 heterologous primers previously developed for the genera Ariocarpus, Echinocactus, Polaskia and Pilosocereus, in four taxa of the genus Cereus: C. fernambucensis subsp. fernambucensis, C. fernambucensis subsp. sericifer, C. jamacaru and C. insularis. Nine microsatellite loci were amplified in Cereus resulting in 35.2% of success in transferability, which is higher than the average rate of 10% reported in the literature for cross-genera transferability in eudicots. The genetic variation in the transferred markers was sufficient to perform standard clustering analysis, indicating each population as a cohesive genetic cluster. Overall, the amount of genetic variation found indicates that the transferred SSR markers might be useful in large-scale population studies within the genus Cereus.