A transient radial cortical microtubule array primes cell division in Arabidopsis
Résumé
Because all cells experience mechanical stress, they have to develop resistance mechanisms to survive. In plants, this notably involves guidance of cellulose deposition by cortical microtubules in the direction of maximal tensile stress. Although the formation of new walls during cell division tends to follow maximal tensile stress direction too, analyses of individual cells over time reveal a much more variable behavior. The origin of such variability, as well as the exact role of interphasic microtubule behavior before cell division have remained mysterious so far. To approach this question, we took advantage of the Arabidopsis stem, where the tensile stress pattern is both highly anisotropic and stable. Although cortical microtubules generally align with maximal tensile stress, we detected a specific time window, ca. 3 hours before cell division, where cells form a radial pattern of cortical microtubules. This pattern was observed in different growth conditions, and was not related to cell geometry or polar auxin transport. Interestingly, this cortical radial pattern correlated with the well-documented increase of cytoplasmic microtubule accumulation before cell division. This radial organization was prolonged in cells of the trm678 mutant, where cortical microtubules are partially disorganized.
Whereas division plane orientation in trm678 is noisier, we found that cell division symmetry was in contrast more precise. We propose that an increased cytoplasmic microtubule accumulation in late G2 disrupts cortical microtubules alignment with tissue stress, allowing the cell to transiently explore its own geometry in order to select a future division plane with correct orientation and symmetry.
In all kingdoms, cells divide according to their own geometry as well as external cues. We discovered a transient stage in plant cells, where part of the division machinery becomes blind to mechanical forces originating from the tissue. Using quantitative imaging and mutant analysis, we propose that this new pre-mitotic stage allows cells to take their own geometry into account and increase the precision of the following division.
Domaines
Sciences du Vivant [q-bio]Origine | Fichiers produits par l'(les) auteur(s) |
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