Abstract
The filamentous algal endophyte Laminarionema elsbetiae is highly prevalent in European populations of the brown alga Saccharina latissima, but has also been found occasionally in the other kelp species Laminaria digitata. The presence of L. elsbetiae coincides with morphological changes in the hosts such as twisted stipes and deformed blades, however, little is known about the molecular bases of these algal host-endophyte interactions. Using a co-cultivation experiment, we showed that physiological and gene regulation responses, and later endophyte prevalences are different between the main and the occasional host. The contact with the endophyte L. elsbetiae induced a stronger and faster transcriptomic regulation in the occasional host L. digitata after 24 h, from which growth rate was later affected. During the first two days of co-cultivation, only 21 differentially expressed genes (DEGs) were common in both kelps, indicating a crucial difference between the molecular responses of the two hosts. By functional annotation, we identified DEGs related to host-endophyte recognition, defense response and cell wall modification. Our results suggest that expression pattern differences between the two kelps related to the recognition of the endophyte and later defense reactions could explain the variability of observed physiological responses and host-endophyte specificity in kelp natural populations.
Highlights
Kelps – including large brown macroalgae of the order Laminariales – are major components of rocky intertidal and subtidal habitats (Wynne and Bold, 1985)
This study provides a first insight into the bases of kelp-endophyte interactions on both physiological and molecular level and highlights the complex and specific cross-talk occurring after the recognition of endophytes by kelps which could explain host specificity
It was reported that algal endophytes can reduce the growth of their hosts by up to 70%, as it has been shown for the red algal endophyte Hypneocolax stellaris in its host, the rhodophyte Hypnea musciformis (Apt, 1984)
Summary
Kelps – including large brown macroalgae of the order Laminariales – are major components of rocky intertidal and subtidal habitats (Wynne and Bold, 1985) They do serve as food source or habitats for animals, and provide a substratum for smaller organisms growing on (epiphytes) or inside (endophytes) of their thalli, such as fungi, oomycetes or filamentous algae (Bartsch et al, 2008; Gachon et al, 2010). Laminariales Responses Upon Endophyte Infection with disease symptoms in their hosts such as twisted stipes, crippled thalli or a reduced growth of the kelps (Peters, 1996; Gauna et al, 2009; Thomas et al, 2009), but the nature of endophytic relationships in different kelps species, from detrimental to neutral ones, is still an open question. It seems that kelpendophyte relationships underlie a certain specificity, but the molecular bases of the interaction between kelps and brown algal endophytes remain poorly understood
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