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Abstract

For the unicellular alga Chlamydomonas reinhardtii, the presence of N-glycosylated
proteins on the surface of two flagella is crucial for both cell-cell interaction during mating and
flagellar surface adhesion. However, it is not known whether only the presence or also the
composition of N-glycans attached to respective proteins is important for these processes. To this
end, we tested several C. reinhardtii insertional mutants and a CRISPR/Cas9 knockout mutant of
xylosyltransferase 1A, all possessing altered N-glycan compositions. Taking advantage of atomic
force microscopy and micropipette force measurements, our data revealed that reduction in
N-glycan complexity impedes the adhesion force required for binding the flagella to surfaces. This
results in impaired polystyrene bead binding and transport but not gliding of cells on solid
surfaces. Notably, assembly, intraflagellar transport, and protein import into flagella are not
affected by altered N-glycosylation. Thus, we conclude that proper N-glycosylation of flagellar
proteins is crucial for adhering C. reinhardtii cells onto surfaces, indicating that N-glycans mediate surface adhesion via direct surface contact.