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キーワード:
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要旨:
Red algae (or Rhodophyta) are a highly diverse phylum of marine organisms in the Archaeplastida kingdom that share a common ancestor with the Viridiplantae lineage (chlorophyte and streptophyte algae plus land plants). Red algae occupy an essential niche as primary producers in marine and freshwater ecosystems across the globe and played a key role in the evolution of other major photosynthetic groups like dinoflagellates, diatoms and brown algae. Fossil evidence also suggests that red algae were one of the first eukaryotic lineages to evolve complex multicellularity, further emphasising their key phylogenetic position in the tree of life. Despite their key ecological and agronomic importance, red algal biology remains virtually unexplored at a molecular level, which has been hampered by the lack of a bona fide red algal model system and the general scarcity of high-quality genomes from the more complex red seaweeds. The Rhodophyta phylogeny currently encompasses 7,461 species but the majority (~95%) belong to just one class called the Florideophyceae. Strikingly, more than one third of all taxa (~36%) are assigned to a single order called the Ceramiales, highlighting an evolutionary radiation that remains to be fully explored. In an effort to develop a novel model system to study red algal development and reproduction, we have generated the first chromosome-level genome assembly for a prominent member of the Ceramiales. Contrary to the commonly held view that red algal genomes are small (up to ~100Mb) with low gene and intron count compared to other lineages, we report significant genome size expansion in this model red alga, which represents the largest and most contiguous red algal genome assembled to date. I will describe our efforts to characterize and trace the genetic and molecular basis for genome size expansion in the Ceramiales, which we hypothesise to be a major source of genetic novelty underpinning the evolutionary success of this highly evolved and species-rich order. This has far-reaching implications for our understanding of red algal ecology, adaptation and evolution, with the genomic resources we are developing for our new red algal model system further promising to reveal new insights into the biology of this important but virtually unexplored group of eukaryotes.
