Mechanical stress contributes to the expression of the STM homeobox gene in Arabidopsis shoot meristems

Abstract

The role of mechanical signals in cell identity determination remains poorly explored in tissues. Furthermore, because mechanical stress is widespread, mechanical signals are difficult to uncouple from biochemical-based transduction pathways. Here we focus on the homeobox gene SHOOT MERISTEMLESS (STM), a master regulator and marker of meristematic identity in Arabidopsis. We found that STM expression is quantitatively correlated to curvature in the saddle-shaped boundary domain of the shoot apical meristem. As tissue folding reflects the presence of mechanical stress, we test and demonstrate that STM expression is induced after micromechanical perturbations. We also show that STM expression in the boundary domain is required for organ separation. While STM expression correlates with auxin depletion in this domain, auxin distribution and STM expression can also be uncoupled. STM expression and boundary identity are thus strengthened through a synergy between auxin depletion and an auxin-independent mechanotransduction pathway at the shoot apical meristem.DOI: http://dx.doi.org/10.7554/eLife.07811.001

Interplay between miRNA regulation and mechanical stress forCUCgene expression at the shoot apical meristem

“…We recently showed that mechanical perturbations in the form of ablation in the SAM is sufficient to induce CUC3 expression in the SAM, while CUC1 expression profile remains largely unaffected in the same conditions. 26 Here we further confirm this result: No significant induction of signal or change in signal patterning was detected in the pCUC1:: CUC1-GFP line after ablation (Fig. 1C upper panels).…”

“…4,15,32 A key question for the future is the analysis of the interplay between mechanical forces and the molecular regulators of meristem function (Fig. 1A).In a recent article, 26 we showed that a master regulator of meristem maintenance, the homeodomain protein SHOOT MERISTEMLESS (STM) is expressed at a higher level in the boundary domain, and that this local increase in promoter activity can be related to mechanical stress: mechanical perturbations are sufficient to induce STM expression in the meristem. Interestingly, mechanical perturbations do not affect all boundary-expressed genes in the same way.…”

“…For instance, the promoter activity of the PINOID gene, which is also increased in the boundary domain, is not affected by mechanical perturbations. 26 Here we focus on the most canonical genetic markers of boundary identity, the CUP SHAPED COTYLEDON (CUC) genes. CUC1, CUC2 and CUC3, belong to a group of NAC domain transcription factors and show a high level of functional redundancy.…”

Cell division plane orientation based on tensile stress inArabidopsis thaliana

“…Stacks of 1,024 × 1,024 pixels of three dissected meristems, with Z slices every 0.5 μm, were acquired every 12 h during 48 h on a Zeiss LSM 700 upright confocal microscope, with a 40× water-dipping lens. Stacks from the kinetics were processed with a C++ script, using the Level Set method (45) to detect the surface of the meristem at high resolution. Meshes of these surfaces were then created with MorphoGraphX (17,46).…”

Direct conversion of root primordium into shoot meristem relies on timing of stem cell niche development

“…Thus, the lock on organ identity probably resides in the final pattern of the meristematic tissues. It might be encoded in the tensile stress networks that characterize different cell arrangements as mechanical forces regulate key meristem factors including STM (Landrein et al, 2015). Alternatively, the size and shape of the lateral organ might alter the distribution of morphogens or the penetration of exogenous cytokinin, as well as other compounds, which control meristem functions.…”