Rhizostomins: A Novel Pigment Family From Rhizostome Jellyfish (Cnidaria, Scyphozoa)

Abstract

Many pigments, such as melanins, are widely distributed throughout the animal kingdom. Others have arisen as novelties in particular lineages, for example, the Green Fluorescent Protein (GFP) found in cnidarians. While GFPs, widely used as fluorescent tags in biomedical research, are the most famous cnidarian example, other novel proteins have also been identified within this phylum. A blue protein that contains a Kringle (KR) domain inserted within a Frizzled cysteine-rich domain (Fz-CRD) was previously described from the jellyfish Rhizostoma pulmo (named rpulFKz1), however little is known about this pigment’s evolution or distribution among cnidarians. We performed a systematic search for homologs of this protein in published genomes and transcriptomes of 93 cnidarians. Phylogenetic analyses revealed eight predicted proteins that possess both domains in the same arrangement and that fall within the same clade as rpulFKz1. The sequence of one of these proteins contains motifs that match sequenced peptides of Cassio Blue, the blue pigment from Cassiopea xamachana. Another one of these proteins belongs to Stomolophus meleagris, and chemical studies on blue pigments that may occur in this genus have shown similarities to rpulFKz1 and Cassio Blue. Therefore, we hypothesize that the eight rpulFKz1 homologs identified are also pigment precursors. All precursors identified were exclusive to jellyfish in the order Rhizostomeae, so we herein name this new pigment family “rhizostomins.” Not all rhizostomes analyzed are blue, however, so these rhizostomin proteins may also be responsible for other colors, or perform other biochemical and biophysical roles. Previous studies have hypothesized that cnidarian pigments are photoprotective, and this study serves as basis for future investigations not only on the function of rhizostomins, but also on potential biotechnological applications for these proteins.

Marine natural products

“…A systematic search of published genomes and transcriptomes of cnidarians for homologues of the blue protein rpulFKz1, originally described from the jellyfish Rhizostoma pulmo , has identified a family of pigment precursors called the rhizostomins specifically associated with jellyfish in the order Rhizostomeae. 601 Not all precursors were associated with blue pigmented organisms, suggesting that the proteins may be responsible for other colours, possibly by modification of the protein/chromophore, or that they confer photoprotection or act in other, as yet unknown roles.…”

The mesoglea buffers the physico-chemical microenvironment of photosymbionts in the upside-down jellyfish Cassiopea sp.

“…Cassiopea contain distinct white striated patterns in dense layers along the rhopalia canals in the bell and under oral arms (see white patches in Figure 1B; Bigelow, 1900). While little is known about host pigments in Cassiopea and other rhizostome jellyfish (Hamaguchi et al, 2021;Lawley et al, 2021), Frontiers in Ecology and Evolution 06 frontiersin.org our reflection data (compare for example rhopalia canal with anastomosing tissue in Figure 2) suggests that the white pigmented tissue can play a role in scattering and reflection of light in Cassiopea medusae, similar to host pigments and the skeleton in reef-building corals (Wangpraseurt et al, 2014a;Jacques et al, 2019). More detailed analyses are required to understand the full potential of lightmodulating host pigments in Cassiopea, and how the holobiont might respond and grow under various light regimes.…”

The mesoglea buffers the physico-chemical microenvironment of photosymbionts in the upside-down jellyfishCassiopeasp

“…Cassiopea contain distinct white striated patterns in dense layers along the rhopalia canals in the bell and under oral arms (see white patches in Figure 1B) (Bigelow, 1900). While little is known about host pigments in Cassiopea and other rhizostome jellyfish (Hamaguchi et al, 2021;Lawley et al, 2021), our reflection data (compare e.g. rhopalia canal with anastomosing tissue in Figure 2) suggests that the white pigmented tissue can play a role in scattering and reflection of light in Cassiopea medusae, similar to host pigments and the skeleton in reef building corals (Wangpraseurt et al, 2014a;Jacques et al, 2019).…”