Intraflagellar transport (IFT) is required for ciliary assembly and maintenance. While disruption of IFT may trigger ciliary disassembly, we show here that IFT mediated transport of a CDK-like kinase ensures proper ciliary disassembly. Mutations in flagellar shortening 2 (FLS2), encoding a CDK-like kinase, lead to retardation of cilia resorption and delay of cell cycle progression. Stimulation for ciliary disassembly induces gradual dephosphorylation of FLS2 accompanied with gradual inactivation. Loss of FLS2 or its kinase activity induces early onset of kinesin13 phosphorylation in cilia. FLS2 is predominantly localized in the cell body, however, it is transported to cilia upon induction of ciliary disassembly. FLS2 directly interacts with IFT70 and loss of this interaction inhibits its ciliary transport, leading to dysregulation of kinesin13 phosphorylation and retardation of ciliary disassembly. Thus, this work demonstrates that IFT plays active roles in controlling proper ciliary disassembly by transporting a protein kinase to cilia to regulate a microtubule depolymerizer.

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16Intraflagellar transport (IFT) is required for ciliary assembly and maintenance. While 17 disruption of IFT may trigger ciliary disassembly, we show here that IFT mediated 18 transport of a CDK-like kinase ensures proper ciliary disassembly. Mutations in 19 flagellar shortening 2 (FLS2), encoding a CDK-like kinase, lead to retardation of cilia 20 resorption and delay of cell cycle progression. Stimulation for ciliary disassembly 21 induces gradual dephosphorylation of FLS2 accompanied with gradual inactivation. 22 Loss of FLS2 or its kinase activity induces early onset of kinesin13 phosphorylation in 23 cilia. FLS2 is predominantly localized in the cell body, however, it is transported to 24 cilia upon induction of ciliary disassembly. FLS2 directly interacts with IFT70 and loss 25 of this interaction inhibits its ciliary transport, leading to dysregulation of kinesin13 26 phosphorylation and retardation of ciliary disassembly. Thus, this work demonstrates 27 that IFT plays active roles in controlling proper ciliary disassembly by transporting a 28 protein kinase to cilia to regulate a microtubule depolymerizer. 29 30 31 Chlamydomonas 3 34 Author Summary 35 Cilia or eukaryotic flagella are cellular surface protrusions that function in cell motility 36 as well as sensing. They are dynamic structures that undergo assembly and 37 disassembly. Cilia are resorbed during cell cycle progression. Dysregulation of cilia 38 resorption may cause delay of cell cycle progression, which underlies aberrant cell 39 differentiation and even cancer. Ciliary resorption requires depolmerization of 40 axonemal microtubules that is mediated by kinesin13. Using the unicellular green alga, 41 Chlamydomonas, we have identified a CDK-like kinase FLS2 that when mutated 42 retards cilia resorption, leading to delay of cell cycle progression. FLS2, a cell body 43 protein, is transported to cilia via intraflagellar transport upon induction of cilia 44 resorption. FLS2 directly interacts with IFT70 and loss of this interaction inhibits 45 transport of FLS2 to cilia and fails to regulate proper phosphorylation of kinesin13 in 46 cilia. 47 50 Cilia are microtubule-based cellular structures that extend from the cell surface. The 51 cellular motility and signaling mediated by cilia plays pivotal roles in physiology and 52 development [1, 2]. The medical importance of cilia is underscored by at least 35 53 ciliopathies that are caused by mutations in around 200 cilia-related genes [3]. 54 55Cilia are dynamic structures that undergo assembly and disassembly. They are 56 assembled after cell division and disassembled prior to and/or during mitosis [4][5][6][7]. 57They are also subjected to disassembly during cell differentiation and in response to 58 cellular stress [8][9][10]. Ciliary disassembly may occur via deflagellation/deciliation 59 (shedding of whole cilium or flagellum) or resorption (gradual shortening from the 60 ciliary tip) depending on physiological context and/or stimulus [8, 11, 12]. During cell 61 cycle progression in mammalian...