Brassinosteroids regulate petal spur length in Aquilegia by controlling cell elongation

Background and Aims Aquilegia produce elongated, three-dimensional petal spurs that fill with nectar to attract pollinators. Previous studies have shown that the diversity of spur length across the Aquilegia genus is a key innovation that is tightly linked with its recent and rapid diversification into new ranges, and that evolution of increased spur lengths are achieved via anisotropic cell elongation. Previous work identified a brassinosteroid response transcription factor as being enriched in the early developing spur cup. Brassinosteroids (BRs) are known to be important for cell elongation, suggesting that brassinosteroid-mediated response may be an important regulator of spur elongation and potentially a driver of spur length diversity in Aquilegia. In this study, we investigated the role of brassinosteroids in the development of the Aquilegia coerulea petal spur. Methods We exogenously applied the biologically active BR brassinolide to developing petals spurs to investigate spur growth under high hormone conditions. We used virus induced gene silencing and gene expression experiments to understand the function of brassinosteroid-related transcription factors in Aquilegia coerulea petal spurs. Key Results We identified a total of three Aquilegia homologs of the BES1/BZR1 protein family and found that these genes are ubiquitously expressed in all floral tissues during development, yet consistent with the previous RNAseq study, we found that two of these paralogs are enriched in early developing petals. Exogenously applied brassinosteroid increased petal spur length due to increased anisotropic cell elongation as well as cell division. We found that targeting of the AqBEH genes with VIGS resulted in shortened petals, a phenotype caused in part by a loss of cell anisotropy. Conclusions Collectively, our results support a role for brassinosteroids in anisotropic cell expansion in Aquilegia petal spurs and highlight the BR pathway as a potential player in the diversification of petal spur length in Aquilegia.

Molecular Dynamics Simulation of Octacosane for Phase Diagrams and Properties via United Atom Scheme

We used united atom scheme to build three types of crystalline structures for octacosane (C28H58) and carried out molecular dynamic simulations to investigate their properties. By gradual heating the three polymorphs, we successfully reproduced the sequence of experimentally reported crystalline phase, intermediate rotator phase and liquid phase. The obtained structural properties of the phases, such as molecule chain morphology, density, chain tilt angle, cell anisotropy. We revealed three mechanisms which well described the kinetic deformation and expansion during the annealing process. Furthermore, our model successfully predicted the melting temperature and the heat of fusion. We also reproduced characteristics of the rotator phases and the liquid phase, indicating the transferability of the united atom scheme among different condensed phases of octacosane. Our methodology represents an effective and efficient means of numerical study for octacosane and may have implication for other members of the n-alkane family.

Cell shape anisotropy and motility constrain self-organised feather pattern fidelity in birds

SummaryCellular self-organisation can emerge from stochastic fluctuations in properties of a developing tissue1–3. This mechanism explains the production of various motifs seen in nature4–7. However, events channelling its outcomes such that patterns are produced with reproducible precision key to fitness remain unexplored. Here, we compared the dynamic emergence of feather primordia arrays in poultry, finch, emu, ostrich and penguin embryos and correlated inter-species differences in pattern fidelity to the amplitude of dermal cell anisotropy in the un-patterned tissue. Using live imaging and ex vivo perturbations in these species, we showed that cell anisotropy optimises cell motility for sharp and precisely located primordia formation, and thus, proper pattern geometry. These results evidence a mechanism through which collective cellular properties of a developmental pattern system ensure stability in its self-organisation and contribute to its evolution.

Perturbative corrections for the scaling of heat transport in a Hele-Shaw geometry and its application to geological vertical fractures

In this work, we investigate numerically the perturbative effects of cell aperture in heat transport and thermal dissipation rate for a vertical Hele-Shaw geometry, which is used as an analogue representation of a planar vertical fracture at the laboratory scale. To model the problem, we derive a two-dimensional set of equations valid for this geometry. For Hele-Shaw cells heated from below and above, with periodic boundary conditions in the horizontal direction, the model gives new nonlinear scalings for both the time-averaged Nusselt number $\langle Nu\rangle _{\unicode[STIX]{x1D70F}}$ and dimensionless mean thermal dissipation rate $\langle \unicode[STIX]{x1D717}\rangle _{\unicode[STIX]{x1D70F}}$ in the high-Rayleigh regime. We demonstrate that $\langle Nu\rangle _{\unicode[STIX]{x1D70F}}$ and $\langle \unicode[STIX]{x1D717}\rangle _{\unicode[STIX]{x1D70F}}$ depend upon the cell anisotropy ratio $\unicode[STIX]{x1D716}$, which measures the ratio between the cell gap and height. We show that $\langle Nu\rangle _{\unicode[STIX]{x1D70F}}$ values in the high-Rayleigh regime decrease when $\unicode[STIX]{x1D716}$ grows, supporting the field observations at the fracture scale. When $\unicode[STIX]{x1D716}\ll 1$, our results are in agreement with the scalings found using the Darcy model. The numerical results satisfy the theoretical relation $\langle Nu\rangle _{\unicode[STIX]{x1D70F}}=Ra\langle \unicode[STIX]{x1D717}\rangle _{\unicode[STIX]{x1D70F}}$, which is obtained from the model. This latter relation is valid for all values of Rayleigh number considered. The perturbative effects of cell aperture are observed only in the exponents of the scalings $\langle Nu\rangle _{\unicode[STIX]{x1D70F}}\sim Ra^{\unicode[STIX]{x1D6FE}(\unicode[STIX]{x1D716})}$ and $\langle \unicode[STIX]{x1D717}\rangle _{\unicode[STIX]{x1D70F}}\sim Ra^{\unicode[STIX]{x1D6FE}(\unicode[STIX]{x1D716})-1}$.

Evolution of spur-length diversity in Aquilegia petals is achieved solely through cell-shape anisotropy

The role of petal spurs and specialized pollinator interactions has been studied since Darwin. Aquilegia petal spurs exhibit striking size and shape diversity, correlated with specialized pollinators ranging from bees to hawkmoths in a textbook example of adaptive radiation. Despite the evolutionary significance of spur length, remarkably little is known about Aquilegia spur morphogenesis and its evolution. Using experimental measurements, both at tissue and cellular levels, combined with numerical modelling, we have investigated the relative roles of cell divisions and cell shape in determining the morphology of the Aquilegia petal spur. Contrary to decades-old hypotheses implicating a discrete meristematic zone as the driver of spur growth, we find that Aquilegia petal spurs develop via anisotropic cell expansion. Furthermore, changes in cell anisotropy account for 99 per cent of the spur-length variation in the genus, suggesting that the true evolutionary innovation underlying the rapid radiation of Aquilegia was the mechanism of tuning cell shape.