Figure 1

Non-seed land plants lack ciliary Y-links. A - Cartoon of cilium structure indicating the basal body (BB), transition zone (TZ) and axoneme. The central pair microtubules (present in motile cilia) and stellate structure (present in Plantae) are shown in grey. B, C - Transmission electron micrographs of axoneme and transition zone architecture in mammals/trypanosomes (B) and non-seed land plants (C). Boxes represent a single enlarged doublet indicated by the asterisk; doublets were rotated to position the ciliary/flagellar membrane towards the top and right of the boxed area. Scale bars = 50 nm. Arrows indicate Y-links visible in mammalian and trypanosome cilia/flagella (B, top 3 panels). Note that these structures are absent in all non-seed plants examined (C, top 6 panels).