Genome-wide identification of TRAF family genes in Urechis unicinctus (Annelida, Echiura) and their responses in resistance to high temperature stress

TRAFs (Tumor necrosis factor receptor-associated factors), serving as important signaling mediators, are essential for organismal immunity and biological responses to environmental stress. Temperature is an important environmental factor for the survival of organisms, but so far, the studies on sequence characteristics of the TRAF family genes and their responses to high temperature stress in marine animals are very limited. In this study, we conducted a genome-wide analysis of the TRAF family genes and revealed their characteristics of responding to high temperature stress in Urechis unicinctus, an economic coastal burrowing Echuran worm. Nine TRAF sequences were identified based on U. unicinctus genome database, which belonged to 5 TRAF members by phylogenetic analysis, namely UuTRAF2, UuTRAF3a, UuTRAF3b, UuTRAF3c, UuTRAF4a, UuTRAF4b, UuTRAF4c, UuTRAF6 and UuTRAF7. Especially, the copy number of TRAF3 and TRAF4 was higher, while the length and number of introns in TRAF2 and TRAF3 were significantly shorter and fewer in U. unicinctus compared to other invertebrates. Furthermore, the expression of the TRAF family genes showed obvious spatio-temporal specificity in the embryos, larvae, and adult tissues of U. unicinctus, with more TRAF family genes expressed in larvae, body wall, and hind-gut. When U. unicinctus adults were stressed by high temperature (29 °C), all the UuTRAFs were significantly up-regulated, especially UuTRAF2 and UuTRAF3a, which were kept at high levels during the experimental phase, indicating their importance in responding to the high temperature stress. Our findings will facilitate a greater comprehension of the sequence characteristics of TRAF family genes in annelids, and provide essential data for future exploring the genetic mechanism and breeding of high temperature tolerance of U. unicinctus.