Séminaire Christophe Colleoni
Deciphering host-symbiont recognition in the photosynthetic association Symsagittifera roscoffensis–Tetraselmis sp. _ lundi 16 juin 2025, 11h00
Deciphering host-symbiont recognition in the photosynthetic association Symsagittifera roscoffensis–Tetraselmis sp.
The marine worm Symsagittifera roscoffensis, or Roscoff worm, establishes a sustainable symbiotic relationship with Tetraselmis algae. First described at the Marine Station of Roscoff (Brittany, France) in the late 19th century, this hermaphroditic flatworm exhibits a vivid green color due to the presence of around 100,000 algae thriving beneath its epidermis. Like most marine photosymbiotic associations, aposymbiotic worms acquire free-living algae from their environment in the days following hatching. The future photosymbionts are engulfed in vacuoles and undergo structural modifications during their migration from the mouth to the periphery, including the loss of flagella, the cell wall, and the eyespot. The ability to subject its photosynthetic partner to mutagenesis, along with the controlled life cycle of S. roscoffensis, and its free-living photosymbionts in the laboratory, provides a powerful forward genetic approach to studying this unique photosymbiosis. In this research project, we investigate the molecular recognition of photosynthetic partners by examining interactions between the algal cell wall and the worm’s lectins. Based on pioneering studies that identified 3-deoxy-D-manno-octulosonic acid (KDO) and 5-O-methyl-KDO (meKDO) as main components of the algal cell wall, we conducted a series of experiments, including reverse mutagenesis on three candidate genes, cks1, cks2, and cks3, which encode three annotated CMP-KDO synthases. Disrupting the cks1/cks2 genes significantly decreased meKDO levels but not KDO, suggesting that Cks activities do not overlap and contribute to cell wall synthesis. Controlled photosymbiosis experiments revealed reduced ingestion efficiency of cks1/cks2 mutants, indicating that alterations in cell wall composition impair the recognition step.
https://ugsf.univ-lille.fr/les-equipes/genetique-microbienne
The marine worm Symsagittifera roscoffensis, or Roscoff worm, establishes a sustainable symbiotic relationship with Tetraselmis algae. First described at the Marine Station of Roscoff (Brittany, France) in the late 19th century, this hermaphroditic flatworm exhibits a vivid green color due to the presence of around 100,000 algae thriving beneath its epidermis. Like most marine photosymbiotic associations, aposymbiotic worms acquire free-living algae from their environment in the days following hatching. The future photosymbionts are engulfed in vacuoles and undergo structural modifications during their migration from the mouth to the periphery, including the loss of flagella, the cell wall, and the eyespot. The ability to subject its photosynthetic partner to mutagenesis, along with the controlled life cycle of S. roscoffensis, and its free-living photosymbionts in the laboratory, provides a powerful forward genetic approach to studying this unique photosymbiosis. In this research project, we investigate the molecular recognition of photosynthetic partners by examining interactions between the algal cell wall and the worm’s lectins. Based on pioneering studies that identified 3-deoxy-D-manno-octulosonic acid (KDO) and 5-O-methyl-KDO (meKDO) as main components of the algal cell wall, we conducted a series of experiments, including reverse mutagenesis on three candidate genes, cks1, cks2, and cks3, which encode three annotated CMP-KDO synthases. Disrupting the cks1/cks2 genes significantly decreased meKDO levels but not KDO, suggesting that Cks activities do not overlap and contribute to cell wall synthesis. Controlled photosymbiosis experiments revealed reduced ingestion efficiency of cks1/cks2 mutants, indicating that alterations in cell wall composition impair the recognition step.
https://ugsf.univ-lille.fr/les-equipes/genetique-microbienne
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