Triant, D. A. | Search bioRxiv

bioRxiv2025

Evolution of highly repetitive silk genes in the Luna moth, Actias luna

Gene duplications are a major driver of molecular diversification and phenotypic evolution. Arthropod silk genes provide an excellent model for studying these processes due to their highly repetitive sequences and rapid evolutionary rates. In Lepidoptera, the Fibroin heavy chain (fibH) gene encodes the primary structural protein for silk fibers, contributing largely to their mechanical strength. This inner fibroin core is surrounded by an outer coating composed primarily of sericins. Sericins are a group of highly repetitive, serine-rich proteins that modulate silk fiber properties. Although sericins in the Domesticated silkworm (Bombyx mori) have been associated with life stage-specific variation in silk characteristics, their evolution and function across Lepidoptera remain poorly understood. Here, we provide a detailed molecular characterization of sericin genes in the Luna moth (Actias luna), a saturniid species known for forming dense, robust, silk-woven cocoons. We identified eight sericin genes that (1) are frequently arranged into clusters of closely related paralogs, (2) exhibit considerable variation in repeat number and amino acid composition, and (3) display distinct gene expression patterns across life stages. A comparison of sericin genes across Saturniidae and Bombycidae reveals evidence for convergent subfunctionalization. These findings suggest that sericin gene duplications enable dynamic shifts in silk composition both within and between species, potentially reflecting adaptive responses to ecological and functional demands. Significance StatementGene duplications are thought to be a major driver of molecular diversification and phenotypic evolution. Arthropod silk genes, characterized by their repetitive sequences and rapid evolution, provide an ideal model for studying these processes. Sericins, a group of highly repetitive, serine-rich silk proteins, are hypothesized to have contributed to the diversification of silk properties, both within and across lepidopteran species. However, their diversity and evolution is poorly understood. Focusing on the Luna moth (Actias luna), we show that sericin gene duplications across Saturniidae have led to subfunctionalization, enabling changes to silk composition. These modifications may represent adaptative responses to ecological and functional demands.

evolutionary biology↗

bioRxiv2021

Rapid shifts in mitochondrial tRNA import in a plant lineage with extensive mitochondrial tRNA gene loss

In most eukaryotes, transfer RNAs (tRNAs) are one of the very few classes of genes remaining in the mitochondrial genome, but some mitochondria have lost these vestiges of their prokaryotic ancestry. Sequencing of mitogenomes from the flowering plant genus Silene previously revealed a large range in tRNA gene content, suggesting rapid and ongoing gene loss/replacement. Here, we use this system to test longstanding hypotheses about how mitochondrial tRNA genes are replaced by importing nuclear-encoded tRNAs. We traced the evolutionary history of these gene loss events by sequencing mitochondrial genomes from key outgroups (Agrostemma githago and Silene [=Lychnis] chalcedonica). We then performed the first global sequencing of purified plant mitochondrial tRNA populations to characterize the expression of mitochondrial-encoded tRNAs and the identity of imported nuclear-encoded tRNAs. We also confirmed the utility of high-throughput sequencing methods for the detection of tRNA import by sequencing mitochondrial tRNA populations in a species (Solanum tuberosum) with known tRNA trafficking patterns. Mitochondrial tRNA sequencing in Silene revealed substantial shifts in the abundance of some nuclear-encoded tRNAs in conjunction with their recent history of mt-tRNA gene loss and surprising cases where tRNAs with anticodons still encoded in the mitochondrial genome also appeared to be imported. These data suggest that nuclear-encoded counterparts are likely replacing mitochondrial tRNAs even in systems with recent mitochondrial tRNA gene loss, and the redundant import of a nuclear-encoded tRNA may provide a mechanism for functional replacement between translation systems separated by billions of years of evolutionary divergence.

evolutionary biology↗