Kinesin-4 optimizes microtubule orientations for responsive tip growth guidance in moss

Tip-growing cells of, amongst others, plants and fungi secrete wall materials in a highly polarized fashion for fast and efficient colonization of the environment. A polarized microtubule cytoskeleton, in which most microtubule ends are directed toward the growing apex, has been implicated in directing growth. Its organizing principles, in particular regarding maintenance of network unipolarity, have remained elusive. We show that a kinesin-4 protein, hitherto best known for a role in cytokinesis, suppresses encounters between antiparallel microtubules. Without this activity, microtubules hyper-aligned along the growth axis and increasingly grew away from the apex. Cells themselves displayed an overly straight growth path and a delayed gravitropic response. This result revealed conflicting systemic needs for a stable growth direction and an ability to change course in response to extracellular cues. Thus, the use of selective inhibition of microtubule growth at antiparallel overlaps constitutes a new organizing principle within a unipolar microtubule array. A kinesin-4-mediated, selective inhibition of microtubule growth at antiparallel overlaps suppresses encounters between antiparallel microtubules in the unipolar microtubule array in tip-growing moss cells. This mechanism constitutes a new organizing principle within unipolar microtubule arrays.

Automated summary

Tip-growing cells of plants and fungi secrete wall materials in a polarized manner for efficient colonization. In this study, a kinesin-4 protein was found to suppress encounters between antiparallel microtubules, leading to a stable growth direction. This discovery provides a new organizing principle within unipolar microtubule arrays.