Recently, a team led by Professor Ke Caihuan and Associate Professor Zhang Yuanye from Xiamen University, in collaboration with Professor Feng Danqing, made significant progress in the field of marine genomics and biofouling research. Their findings were published in Nature Genetics. The study analyzed the attachment and shell formation processes of the representative marine biofouling organism, tunicates, and revealed the origin and function of the new genes bcs-6 and bsf. These new genes provide a crucial genetic basis for organisms to adapt to unique habitats, offering important insights for marine antifouling technologies and biomimetic material development.
Tunicates, known as the "flat-laying heroes" of the ocean, are the only group of crustaceans that live a sessile lifestyle. Charles Darwin spent eight years observing and studying tunicates 170 years ago. Today, this fascinating organism continues to inspire biologists and materials scientists. Tunicates can secrete tunicate glue, which rapidly solidifies in water, making it an important biomimetic material. However, their attachment to surfaces such as ships and aquaculture nets causes significant damage, making them representative biofouling organisms.
The attachment and adaptation to a sessile lifestyle in tunicates involve unique traits formed during the process of adapting to specific habitats. The genetic basis of these unique traits may stem from new genes that evolved within the group during the evolutionary process. These genes consist of unknown sequences lacking corresponding functional information in current databases, posing a significant challenge in identifying and deciphering their functions.
The study obtained the chromosome-level genome of tunicates. Among the 26 expanded gene families, 3 are related to attachment, and 9 are related to shell formation. Members of the Hox gene family, Hox3 and abd-A, are lost in the tunicate genome, possibly due to the degeneration of predatory and swimming organs to adapt to a benthic sessile lifestyle.
The study serendipitously discovered a highly expressed gene, bcs-6, during the tunicate attachment process, which possesses a complete transposon structure. This structure belongs to a miniature terminal repeat retrotransposon, and the high expression of the tunicate transposon structural gene is attributed to the acquisition of a TATA box and a cis-regulatory element, CRE2 (CACGTG), during evolution, leading to gene duplication in the genome. The transposon structural gene is expressed in the oil droplet cells of tunicate larvae, binding to proteins related to the tricarboxylic acid cycle and glycolysis, regulating the endogenous energy supply during the attachment process. The transposon structure plays a crucial role in attachment.
The study indicates that transposons not only contribute fragments to genes or gene regulatory systems but can also transform into new genes and functions by acquiring promoters and cis-regulatory elements, updating our understanding of transposons.
Furthermore, the study identified a new gene, bsf, highly expressed in the mantle, a critical tissue for tunicate shell formation. The protein encoded by bsf contains 7 repetitive motifs, each capable of forming 4 reverse parallel β-fold structures. The recombinant protein can self-assemble into filamentous fibers in water, tightly binding to chitin and aragonite. The study proposed a mechanism model for tunicate shell formation. Investigating the evolutionary characteristics of the bsf gene that adapt to specific environments aids in developing biomimetic materials with special adhesive properties in aquatic environments.
The research received joint funding from the National Natural Science Foundation of China and the National Key Research and Development Program.
For more information on the paper, please visit: https://doi.org/10.1038/s41588-024-01733-7
