Parthenosporophytes of the brown alga Ectocarpus siliculosus exhibit sex-dependent differences in thermotolerance as well as fatty acid and sterol composition

Abstract

In the filamentous brown alga Ectocarpus siliculosus, male and female sex is expressed during the haploid parthenosporophyte phase of the life cycle. Here, we found that male parthenosporophytes displayed thermotolerance whereas female specimens displayed severely reduced viability at 25 °C and 28 °C. Profiling of polyunsaturated fatty acids showed that n-3 and n-6 were the predominant species in male and female parthenosporophytes, respectively, and that the n-3/n-6 fatty acid ratio was not affected by a temperature change. Both male and female parthenosporophytes contained the sterols fucosterol, cholesterol, and ergosterol, but these were present at higher levels at 10-25 °C in female specimens than in males. Thus, these fatty acids and sterols would be expected to make the membranes more rigid in the female compared to the male, which is opposite to the paradigm that increased rigidity confers thermotolerance. Our results suggest that the sex-dependent thermotolerance in E. siliculosus parthenosporophytes is not explained by the relationship between membrane fluidity and differences in fatty acids and sterol compositions.

Semi-Quantitative Targeted Gas Chromatography-Mass Spectrometry Profiling Supports a Late Side-Chain Reductase Cycloartenol-to-Cholesterol Biosynthesis Pathway in Brown Algae

“…The four brown algae for which, we already reconstructed a GSMN illustrate well the classical challenge of heterogeneous data integration. For the two Ectocarpus species, we had GC-MS profiling data, partially overlapping, but also partially contradicting those published by others (Mikami et al, 2018). For S. japonica, the published sterol profiles (Honya et al, 1994) were in agreement with our own observations in the closely related S. latissima.…”

“…Among the other investigated sterols, lanosterol was never found, whereas 24-ethylcholesterol and lathosterol were found only in the three red algal species, and zymosterol was found only in P. palmata and in E. subulatus. The fact that we did not detect ergosterol in any of the analyzed algae was particularly striking because it was recently reported to be present in E. siliculosus, using a different separation technique, HPLC coupled to fluorescence detection (Mikami et al, 2018). Therefore, we checked using a spiked extract that we were technically able to identify the standard in an extract from E. siliculosus tissue (Supplementary Figure S1).…”

“…Finally, to explain the observation of 24-ethylcholest-22-enol in some brown algae, it is necessary to infer the presence of 24-ethylcholesterol as an intermediate, because in that case the lack of Δ 24(25) or Δ 24(28) would render impossible a sterol-28-methylation from 24-methylcholest-22-enol. Actually, 24-ethylcholesterol has been reported in other brown algae by different groups (Kamenarska et al, 2003;Lopes et al, 2011;Mikami et al, 2018).…”

“…The main brown algal sterol is fucosterol, but C28 and C27 sterols have also been reported, for example, in the model brown alga Ectocarpus siliculosus (Mikami et al, 2018). Among C27 derivatives, specialized metabolites have also been identified, such as a molecule bearing structural similarity to a brassinosteroid biosynthesis precursors in the fucale Cytoseira myrica (Hamdy et al, 2009), or the mozukulins from another ectocarpale species, the mozuku Cladosiphon okamuranus (Cheng et al, 2016).…”

Heat‐stress Memory is Responsible for Acquired Thermotolerance inBangia fuscopurpurea

“…Letters denote statistically significant differences ( P < 0.05) as determined by one‐way ANOVA as described in Mikami et al. ().…”