The Ectocarpus IMMEDIATE UPRIGHT gene encodes a member of a novel family of cysteine-rich proteins with an unusual distribution across the eukaryotes

Abstract

The sporophyte generation of the brown alga Ectocarpus sp. exhibits an unusual pattern of development compared with the majority of brown algae. The first cell division is symmetrical and the apical-basal axis is established late in development. In the immediate upright (imm) mutant, the initial cell undergoes an asymmetric division to immediately establish the apical-basal axis. We provide evidence which suggests that this phenotype corresponds to the ancestral state of the sporophyte. The IMM gene encodes a protein of unknown function that contains a repeated motif also found in the EsV-1-7 gene of the Ectocarpus virus EsV-1. Brown algae possess large families of EsV-1-7 domain genes but these genes are rare in other stramenopiles, suggesting that the expansion of this family might have been linked with the emergence of multicellular complexity. EsV-1-7 domain genes have a patchy distribution across eukaryotic supergroups and occur in several viral genomes, suggesting possible horizontal transfer during eukaryote evolution.

DISTAG/TBCCd1 Is Required for Basal Cell Fate Determination in Ectocarpus

“…Several observations indicate that this basal network of prostrate filaments is equivalent to the basal system of the gametophyte generation, represented by the rhizoid: (1) both structures develop at the base of the alga (in contact with the substratum), (2) both structures serve an anchoring function, and (3) in sporophytes carrying the immediate upright (imm) mutation the system of prostrate filaments is homeotically replaced by a rhizoid similar to that of the gametophyte (Peters et al, 2008;Macaisne et al, 2017).…”

“…We recently adapted this Fucus RNAi protocol for Ectocarpus, using synthetic siRNA molecules instead of long double-stranded RNA molecules and a lipofectant specifically adapted for dsRNA delivery to introduce the siRNAs into the cell rather than the microinjection procedure used for Fucus (Macaisne et al, 2017).…”

“…A high-quality genome sequence is available for this species Cormier et al, 2017), together with extensive transcriptomic data Luthringer et al, 2015) and genetic tools including a dense genetic map (Heesch et al, 2010;Avia et al, 2017). Genetic transformation is not yet possible, but gene knockdown using RNA interference has been demonstrated (Macaisne et al, 2017). These various tools were employed in a recent study that was the first to identify a brown algal developmental gene using a forward genetic approach (Macaisne et al, 2017).…”

“…Genetic transformation is not yet possible, but gene knockdown using RNA interference has been demonstrated (Macaisne et al, 2017). These various tools were employed in a recent study that was the first to identify a brown algal developmental gene using a forward genetic approach (Macaisne et al, 2017).…”

Seaweed reproductive biology: environmental and genetic controls

“…Results have been published on two mutants, immediate upright (imm) and ouroboros (oro). The imm mutant exhibits partial conversion of the sporophyte generation into a gametophyte during early development, and the oro mutant generates a homeotic conversion of the sporophyte generation into a fully functional gametophyte (Peters et al 2008, Coelho et al 2011, Macaisne et al 2017. Ongoing studies focus on detecting the genes underlying the imm and oro mutants, which would allow comparison of the diploid program with other model systems.…”