# Transcriptome Analysis of Differentially Expressed Genes in Freshwater Pearl Mussel (Sinohyriopsis cumingii) with Four Different Shell Colors

## TL;DR

This study identifies genes linked to shell and pearl color variation in freshwater mussels, offering insights for selective breeding to produce pearls with desired colors.

## Contribution

The study reveals specific genes and pathways responsible for shell and pearl coloration in Sinohyriopsis cumingii.

## Key findings

- Key genes involved in pigment metabolism show differential expression across shell colors.
- Genes related to mineral metabolism and absorption also exhibit significant variation.
- These genes influence melanin, carotenoids, porphyrins, and heme, affecting color formation.

## Abstract

Pearl culture is a significant global industry, with China being a leading producer in utilizing the freshwater mussel Sinohyriopsis cumingii. The color of the pearl is closely linked to the shell color of the mussel, yet the molecular genetic basis driving this variation remains unclear. This study investigated the mechanisms underlying shell and pearl coloration by analyzing the transcriptomes of juvenile S. cumingii with four distinct inner-shell colors. The results revealed significant differential expression of key genes regulating pigment metabolism, and genes involved in mineral metabolism and absorption. These findings indicate that shell color phenotypes are under stable genetic control, with the identified genes directly influencing color formation through pigment deposition and mineral integration. This study shows that specific genetic pathways govern color variation in S. cumingii, providing a molecular foundation for selective breeding. This knowledge holds considerable social and economic value, as it enables the targeted cultivation of mussels to produce pearls with desirable and consistent colors, thereby enhancing product quality, market value, and sustainability for the global pearl industry.

Pearl culture has long been a major global industry. As a significant global producer, China mainly produces pearls from the freshwater mussel (Sinohyriopsis cumingii). S. cumingii with various shell colors can produce pearls of different colors; for example, mussels with a blue-white shell can produce white pearls, while those with a purple shell can produce light-purple pearls. Therefore, investigating the molecular genetics of shell color variation in S. cumingii can advance our understanding of the mechanisms underlying differences in shell and pearl coloration in these mussels. In this study, we selected juvenile S. cumingii with four differently colored inner shells and collected tissue samples for transcriptomic analysis. The results showed that many key genes involved in the regulation of pigment metabolism (such as ADAMTS, TYR, BCDO2, and FTH1), as well as those associated with metabolism and mineral absorption (such as TRPV6, HCP1, HEPH, and Zip4), exhibited significant differences. Furthermore, these DEGs (differentially expressed genes) may influence the synthesis and metabolism of melanin, carotenoids, porphyrins, and heme, thereby affecting shell color variation; they might also be one of the potential reasons why S. cumingii produces pearls of different colors.