Intraspecific Diversity in the Cold Stress Response of Transposable Elements in the Diatom Leptocylindrus aporus

Abstract

Transposable elements (TEs), activated as a response to unfavorable conditions, have been proposed to contribute to the generation of genetic and phenotypic diversity in diatoms. Here we explore the transcriptome of three warm water strains of the diatom Leptocylindrus aporus, and the possible involvement of TEs in their response to changing temperature conditions. At low temperature (13 • C) several stress response proteins were overexpressed, confirming low temperature to be unfavorable for L. aporus, while TE-related transcripts of the LTR retrotransposon superfamily were the most enriched transcripts. Their expression levels, as well as most of the stress-related proteins, were found to vary significantly among strains, and even within the same strains analysed at different times. The lack of overexpression after many months of culturing suggests a possible role of physiological plasticity in response to growth under controlled laboratory conditions. While further investigation on the possible central role of TEs in the diatom stress response is warranted, the strain-specific responses and possible role of in-culture evolution draw attention to the interplay between the high intraspecific variability and the physiological plasticity of diatoms, which can both contribute to the adaptation of a species to a wide range of conditions in the marine environment.Genes 2020, 11, 9 2 of 25 (3) both of the above, as plasticity can be adaptive with respect to a function and may be altered by natural selection and ultimately become or facilitate adaptation.In addition to natural environmental variability, diatoms used in experimental research are also exposed to another source of variability; they are removed from their natural environment, isolated and transferred to laboratory conditions in which evolutionary processes do not cease to occur [8]. Many cases of novel genetic variation have been shown after years of maintenance in culture collection [9][10][11]. Considering the high adaptability of diatoms, it could be hard to interpret the intra-specific algal diversity observed in related studies as the result of (a) adaptation to the natural environment from which strains were isolated or (b) evolutionary changes while being in culture.Temperature is a very significant environmental variable that affects the physiological response of diatoms and ultimately determines their phenological patterns and geographic ranges [12][13][14], as well as one of the parameters that is usually kept constant in culture conditions. An increase in temperature leads to an increase in enzyme activity in metabolic processes, including photosynthesis and respiration, so the cells are expected to grow faster. Even algae obtained from cold habitats have shown at least short-term temperature optima for photosynthesis several degrees higher than the temperature at which they were growing. Low temperatures lead to the exact opposite direction so that, in order to survive, cells respond with an increase in enzyme synthesis [15,16]. A recent study ...

Surviving Heatwaves: Thermal Experience Predicts Life and Death in a Southern Ocean Diatom

“…These results are in line with previous studies that have used genomic and transcriptomic approaches to characterize the thermal adaptations of Southern Ocean diatoms, demonstrating that cells may employ common stress mechanisms at both thermal extremes (Mock et al, 2017;Pargana et al, 2020). Growth of Fragilariopsis cylindrus under both thermal extremes (−2, +11 • C) revealed similarities in altered gene expression relative to ambient conditions, indicating that generic stress responses were potentially employed in both thermal environments (Mock et al, 2017), and in Leptocylindrus aporus, expression of heat shock proteins (HSPs) was upregulated in both high and low temperature incubations (Pargana et al, 2020). The production of HSPs is known to increase during growth above T opt (Rousch et al, 2004;Leung et al, 2017), and has been shown to be maximized as temperatures approach thermal maxima (T max ) (Low et al, 2018).…”

Surviving heatwaves: thermal experience predicts life and death in a Southern Ocean diatom

“…We therefore hypothesize that thermal stress experienced at heatwave temperatures acted to enhance growth both at low (-2.2, -0.4 o C) and high (7.6 o C) thermal extremes (Figure 3). This idea is in line with previous studies that have used genomic and transcriptomic approaches to characterise the thermal adaptations of diatoms to the Southern Ocean, demonstrating that common stress mechanisms can be employed at both thermal extremes (Mock et al, 2017, Pargana et al, 2020. Growth of Fragilariopsis cylindrus under both thermal extremes (-2, +11 o C) revealed similarities in altered gene expression relative to ambient conditions, indicating that generic stress responses were potentially employed in both thermal environments (Mock et al, 2017), and Leptocylindrus aporus cultured at high and low temperatures revealed that the expression of heat shock proteins were upregulated under both thermal regimes (Pargana et al, 2020).…”

“…This idea is in line with previous studies that have used genomic and transcriptomic approaches to characterise the thermal adaptations of diatoms to the Southern Ocean, demonstrating that common stress mechanisms can be employed at both thermal extremes (Mock et al, 2017, Pargana et al, 2020. Growth of Fragilariopsis cylindrus under both thermal extremes (-2, +11 o C) revealed similarities in altered gene expression relative to ambient conditions, indicating that generic stress responses were potentially employed in both thermal environments (Mock et al, 2017), and Leptocylindrus aporus cultured at high and low temperatures revealed that the expression of heat shock proteins were upregulated under both thermal regimes (Pargana et al, 2020). The production of HSPs is known to increase during growth above Topt (Leung et al, 2017, Rousch et al, 2004, and has been shown to be maximised as temperatures approach thermal maxima (Tmax) (Low et al, 2018).…”

Physiological and molecular responses to ocean acidification among strains of a model diatom

“…As pCO 2 increases, Pt4 may reduce HCO − 3 acquisition more preferentially than other strains, which would save more energy consumed by CCMs. However, the strains used in this study have been transferred from their local natural environment to laboratory conditions for several decades, in which evolutionary processes do not cease to occur (Lakeman et al 2009;Pargana et al 2020). Therefore, to better explore strain-specific response to ocean acidification, molecular and physiological experiments in both laboratory and field should be conducted using more recently isolated strains in the future.…”