(a) Localization of DYF-19, HYLS-1, GASR-8 and K10G6.4 in tail phasmid cilia. Each phasmid organ contains two cilia bundled together40. Images show the ciliary base of one set of two phasmid cilia expressing mCherry-tagged DYF-19 and GFP-tagged candidate proteins as indicated. HYLS-1 and GASR-8 localize proximal to DYF-19 in the region of the degenerated basal body, whereas K10G6.4 completely co-localizes with DYF-19 on TFs. (b) Cartoon illustrating the relative localization of DYF-19, HYLS-1, GASR-8 and K10G6.4 at the ciliary base. (c) Dye-filling of phasmid cilia was used to analyse cilia integrity. hyls-1 and dyf-19 mutants are dye-fill defective, whereas gasr-8 and k10g6.4 mutants possess apparently normal cilia. More than 200 worms analysed for each genetic background. (d–i) HYLS-1 is required for proper localization of DYF-19, GASR-8 and K10G6.4. Phasmid cilia expressing fluorescently tagged DYF-19 (d), GASR-8 (f) and K10G6.4 (h) in WT and hyls-1 mutants. NPHP-1 (d,f) and MKS-5 (h) were used to label the TZ. Quantification of relative fluorescence intensities of DYF-19 (e), GASR-8 (g) and K10G6.4 (i) in cilia of WT and hyls-1 mutants. n represents number of cilia analysed. (j) BB remnant and TFs are missing at the base of hyls-1 amphid cilia. Scalebars, 200 nm (j), 1 μm (other panels). Error bars indicate s.d. Student's t-test indicates significant differences; *P<0.01 and ***P<0.001.