Exploring Transposons in macroalgae: LTR elements and neighbouring genes in red seaweeds

Pilar Garcia-JimenezRafael R. Robaina^*

• University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain

The discovery of transposable elements (TEs) or transposons by Barbara McClintock in 1949 has led to the understanding that these elements play a pivotal role in the evolution and genetic variability of organisms. TEs are classified into two main classes: Class I, or retrotransposons, are transposed through an RNA intermediate, whereas Class II are mobilised directly through DNA. The influence of TEs on gene expression is considerable, as their insertion near or within genes can result in alterations to their functionality. Due to their disruptive role, organisms have evolved regulatory mechanisms to control their activity, particularly under conditions of stress, where the activation of TEs seems to be trigger and it can result in mutations. Regarding marine macroalgae, TEs also play a significant role in the structure of the genome, although there is currently a paucity of knowledge regarding their dynamics. In this study, TEs were annotated and characterised in seventeen publicly available, non-annotated algal genomes using the new powerful pipeline Earlgrey to quantify their diversity and activity over time. The results demonstrated a diverse range of presence and diversity among the red, brown, and green algae. In the case of red algae, retrotransposons of the LTR type were found to be the most abundant. Further analysis with a local script revealed that many LTRs were found near or within hundreds of hits in three protein databases, with a multiplicity of functions. The most frequently identified were LTR-specific enzymes, such as Ribonuclease H, alongside nucleic acid-binding proteins, and cation-binding proteins (e.g., CCHC-type zinc-finger proteins, haem peroxidase superfamily), which play key roles in mitigating recurrent marine ionic stress. The colocalization of transposable elements (TEs) with stress-responsive proteins raises a compelling question: does stress-induced activation of these proteins modulate LTR activity as a regulatory safeguard, or has the LTR been functionally assimilated into the cellular network, facilitating protein expression as part of the adaptive stress response?This perspective unveils a promising avenue for investigating the functional integration of TEs in cellular resilience, with potential implications for understanding the evolutionary dynamics of stress adaptation.