Autophagy regulates the formation of primary cilia, which in turn affects autophagy. The relationship between autophagy and cilia is known to be bidirectional although the specific mechanisms involved have yet to be elucidated. In this study, we found for the first time that ATG8 protein localizes in the basal body of the dorsal kineties and the base of the ventral cirri in Euplotes amieti. ATG8 protein maintains the structural integrity of cilia and plays a role in the construction of the cortical ciliature and microtubule cytoskeleton associated with cilia. ATG8 gene interference leads to the degradation of IFT88, the transport protein in cilia, thus inhibiting the generation of cilia, and affecting the swing of cilia. This influences the swimming speed and cilia pattern, leading to death in Euplotes amieti.

Ultraviolet-B (UV-B) radiation is one of the important environmental factors limiting plant growth. Both abscisic acid (ABA) and microtubules have been previously reported to be involved in plant response to UV-B. However, whether there is a potential link between ABA and microtubules and the consequent signal transduction mechanism underlying plant response to UV-B radiation remains largely unclear. Here, by using sad2-2 mutant plants (sensitive to ABA and drought) and exogenous application of ABA, we saw that ABA strengthens the adaptive response to UV-B stress in Arabidopsis thaliana (A. thaliana). The abnormal swelling root tips of ABA-deficient aba3 mutants demonstrated that ABA deficiency aggravated the growth retardation imposed by UV-B radiation. In addition, the cortical microtubule arrays of the transition zones of the roots were examined in the aba3 and sad2-2 mutants with or without UV-B radiation. The observation revealed that UV-B remodels cortical microtubules, and high endogenous ABA can stabilize the microtubules and reduce their UV-B-induced reorganization. To further confirm the role of ABA on microtubule arrays, root growth and cortical microtubules were evaluated after exogenous ABA, taxol, and oryzalin feeding. The results suggested that ABA can promote root elongation by stabilizing the transverse cortical microtubules under UV-B stress conditions. We thus uncovered an important role of ABA, which bridges UV-B and plants\' adaptive response by remodeling the rearrangement of the cortical microtubules.

The organization of the microtubule cytoskeleton is critical for cell and organ morphogenesis. The evolutionarily conserved microtubule-severing enzyme KATANIN plays critical roles in microtubule organization in the plant and animal kingdoms. We previously used conical cell of Arabidopsis thaliana petals as a model system to investigate cortical microtubule organization and cell morphogenesis and determined that KATANIN promotes the formation of circumferential cortical microtubule arrays in conical cells. Here, we demonstrate that the conserved protein phosphatase PP2A interacts with and dephosphorylates KATANIN to promote the formation of circumferential cortical microtubule arrays in conical cells. KATANIN undergoes cycles of phosphorylation and dephosphorylation. Using co-immunoprecipitation coupled with mass spectrometry, we identified PP2A subunits as KATANIN-interacting proteins. Further biochemical studies showed that PP2A interacts with and dephosphorylates KATANIN to stabilize its cellular abundance. Similar to the katanin mutant, mutants for genes encoding PP2A subunits showed disordered cortical microtubule arrays and defective conical cell shape. Taken together, these findings identify PP2A as a regulator of conical cell shape and suggest that PP2A mediates KATANIN phospho-regulation during plant cell morphogenesis.

IQ67-domain (IQD) proteins, first identified in Arabidopsis and rice, are plant-specific calmodulin-binding proteins containing highly conserved motifs. They play a critical role in plant defenses, organ development and shape, and drought tolerance. Driven by comprehensive genome identification and analysis efforts, IQDs have now been characterized in several species and have been shown to act as microtubule-associated proteins, participating in microtubule-related signaling pathways. However, the precise molecular mechanisms underpinning their biological functions remain incompletely understood. Here we review current knowledge on how IQD family members are thought to regulate plant growth and development by affecting microtubule dynamics or participating in microtubule-related signaling pathways in different plant species and propose some new insights.

Upon water uptake and release of seed dormancy, embryonic plant cells expand, while being mechanically constrained by the seed coat. Cortical microtubules (CMTs) are key players of cell elongation in plants: their anisotropic orientation channels the axis of cell elongation through the guidance of oriented deposition of load-bearing cellulose microfibrils in the cell wall. Interestingly, CMTs align with tensile stress, and consistently, they reorient upon compressive stress in growing hypocotyls. How CMTs first organise in germinating embryos is unknown, and their relation with mechanical stress has not been investigated at such an early developing stage.
Here, we analysed CMT dynamics in dormant and non-dormant Arabidopsis seeds by microscopy of fluorescently tagged microtubule markers at different developmental time points and in response to abscisic acid and gibberellins. We found that CMTs first appear as very few thick bundles in dormant seeds. Consistently, analysis of available transcriptome and translatome datasets show that limiting amounts of tubulin and microtubule regulators initially hinder microtubule self-organisation. Seeds imbibed in the presence of gibberellic acid or abscisic acid displayed altered microtubule organisation and transcriptional regulation. Upon the release of dormancy, CMTs then self-organise into multiple parallel transverse arrays. Such behaviour matches the tensile stress patterns in such mechanically constrained embryos. This suggests that, as CMTs first self-organise, they also align with shape-derived tensile stress patterns.
Our results provide a scenario in which dormancy release in the embryo triggers microtubule self-organisation and alignment with tensile stress prior to germination and anisotropic growth.