Abstract
BackgroundMicrotubules (MTs) are polarized polymers with highly dynamic plus ends that stochastically switch between growth and shrinkage phases. In eukaryotic cells, a plethora of MT-associated proteins (MAPs) regulate the dynamics and higher-order organization of MTs to mediate distinct cellular functions. Plus-end tracking proteins (+TIPs) are a group of MAPs that specifically accumulate at the growing MT plus ends, where they modulate the behavior of the MT plus ends and mediate interactions with cellular targets. Although several functionally important + TIP proteins have been characterized in yeast and animals, little is known about this group of proteins in plants.ResultsWe report here that two homologous MAPs from Arabidopsis thaliana, Growing Plus-end Tracking 1 (GPT1) and GPT2 (henceforth GPT1/2), contain basic MT-binding regions at their central and C-terminal regions, and bind directly to MTs in vitro. Interestingly, GPT1/2 preferentially accumulated at the growing plus ends of cortical MTs in interphase Arabidopsis cells. When the GPT1/12-decorated growing plus ends switched to rapid depolymerization, GPT1/2 dissociated from the MT plus ends. Conversely, when the depolymerizing ends were rescued and started to polymerize again, GPT1/2 were immediately recruited to the growing MT tips. This tip tracking behavior of GPT proteins does not depend on the two established plant + TIPs, End-Binding protein 1 (EB1) and SPIRAL1 (SPR1).ConclusionsThe Arabidopsis MAPs GPT1 and GPT2 bind MTs directly through their basic regions. These MAPs track the plus ends of growing MTs independently of EB1 and SPR1 and represent a novel plant-specific + TIP family.
Highlights
Microtubules (MTs) are polarized polymers with highly dynamic plus ends that stochastically switch between growth and shrinkage phases
The amino acid sequences of Growing Plus-end Tracking 1 (GPT1) and Growing Plus-end Tracking 2 (GPT2) ( GPT1/2) share 59.8% similarity and 46.1% identity, and do not contain any defined domains with known functions. We demonstrate that these GPT proteins are novel plantspecific + Plus-end tracking proteins (TIPs) that track growing MT plus ends independently of End-Binding protein 1 (EB1) and SPR1
MT-binding regions in GPT1/2 GPT1/2 do not exhibit any significant amino acid homology with functionally characterized proteins [21], we noticed that the middle (M) and C-terminal (C) regions of these proteins are enriched in the basic amino acid residues Arg, Lys, and His (18.9% in GPT1 and 17.9% in GPT2; Fig. 1a and b)
Summary
Microtubules (MTs) are polarized polymers with highly dynamic plus ends that stochastically switch between growth and shrinkage phases. A plethora of MT-associated proteins (MAPs) regulate the dynamics and higher-order organization of MTs to mediate distinct cellular functions. Microtubules (MTs) are highly conserved polarized cytoskeletal polymers that mediate cellular processes such as motility, cell division, polarity, intracellular transport, and signaling in eukaryotic cells. GTP-bound α/β-tubulin heterodimers are stacked in a head-to-tail fashion to form polar protofilaments, which associate laterally to form polar hollow MT cylinders with highly dynamic plus ends and more stable minus ends. The GTP-bound tubulin forms a cap that stabilizes the plus end of the MT and thereby promotes its growth. GTP hydrolysis and subsequent phosphate release occur soon after tubulin incorporation into the protofilament, resulting in a short GTP cap [4]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
