TRANSCRIPTOME PROFILING OF THREE DIFFERENT LIFE CYCLE PHASES OF THE BLOOM-FORMING MARINE MICROALGA Emiliania huxleyi

Shai Fainsod 1,2 Omer Murik 3 Miguel J. Frada 1,2
1IUI, The Interuniversity Institute for Marine Sciences of Eilat, Eilat, Israel
2Ecology, Evolution and Behavior - Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
3Plant & Environmental Sciences - Alexander Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel

Emiliania huxleyi (coccolithophore) is a cosmopolitan microalga that forms extensive blooms in the oceans of large ecological and biogeochemical impact [1,2]. E. huxleyi displays a haplodiplontic sexual life cycle, composed of diploid (2N) and haploid (1N) cells with contrasting morpho-physiological properties, both capable of independent mitotic growth. 2N cells are nonmotile, distinctively covered with calcareous plates (coccoliths), are associated with bloom formation and sensitive to specific viruses (EhV) that terminate the blooms, compared to 1N cells that are noncalcified, biflagellate and EhV-resistant. Strikingly, it was recently shown that during EhV-infection, 2N cells (strain RCC 1216) can switch to a viral-resistant phase resembling 1N cells. It is possible that a mechanism of phenotype remodeling, decoupled from ploidy, may enhance survival rates of E. huxleyi EhV-infected blooms [3]. To characterize the degree of life-phase differentiation and the potential drivers of phenotype switch, we compared the transcriptome profiles of 2N, 1N and the novel 2N decoupled-phenotype strains. We firstly assembled de-novo the transcriptomes and found a large variability in gene expression between life cycle phases, but also phase-specific transcripts. The progress of these analyses will foster our understanding of the extent of genetic and physiological differentiation between life cycle phases and of viral resistant mechanisms in this important phytoplankton. Finally, it will also enable the development of gene-markers to assess the life cycle dynamics of E. huxleyi at sea.

1. Brown, Christopher W., and James A. Yoder. "Coccolithophorid blooms in the global ocean." Journal of Geophysical Research: Oceans 99.C4 (1994): 7467-7482.

2. Laber, Christien P., et al. "Coccolithovirus facilitation of carbon export in the North Atlantic." Nature microbiology (2018): 1.

3. Frada, Miguel José, et al. "Morphological switch to a resistant subpopulation in response to viral infection in the bloom-forming coccolithophore Emiliania huxleyi." PLoS pathogens 13.12 (2017): e1006775.









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