2,502 research outputs found
The juxtamembrane and carboxy-terminal domains of Arabidopsis PRK2 are critical for ROP-induced growth in pollen tubes.
Polarized growth of pollen tubes is a critical step for successful reproduction in angiosperms and is controlled by ROP GTPases. Spatiotemporal activation of ROP (Rho GTPases of plants) necessitates a complex and sophisticated regulatory system, in which guanine nucleotide exchange factors (RopGEFs) are key components. It was previously shown that a leucine-rich repeat receptor-like kinase, Arabidopsis pollen receptor kinase 2 (AtPRK2), interacted with RopGEF12 for its membrane recruitment. However, the mechanisms underlying AtPRK2-mediated ROP activation in vivo are yet to be defined. It is reported here that over-expression of AtPRK2 induced tube bulging that was accompanied by the ectopic localization of ROP-GTP and the ectopic distribution of actin microfilaments. Tube depolarization was also induced by a potentially kinase-dead mutant, AtPRK2K366R, suggesting that the over-expression effect of AtPRK2 did not require its kinase activity. By contrast, deletions of non-catalytic domains in AtPRK2, i.e. the juxtamembrane (JM) and carboxy-terminal (CT) domains, abolished its ability to affect tube polarization. Notably, AtPRK2K366R retained the ability to interact with RopGEF12, whereas AtPRK2 truncations of these non-catalytic domains did not. Lastly, it has been shown that the JM and CT domains of AtPRK2 were not only critical for its interaction with RopGEF12 but also critical for its distribution at the plasma membrane. These results thus provide further insight into pollen receptor kinase-mediated ROP activation during pollen tube growth
Constraining neutrino mass in dynamical dark energy cosmologies with the logarithm parametrization and the oscillating parametrization
We constrain two dynamical dark energy models that are parametrized by the
logarithm form of
and the oscillating form of
. Comparing with
the Chevallier-Polarski-Linder (CPL) model, the two parametrizations for dark
energy can explore the whole evolution history of the universe properly. Using
the current mainstream observational data including the cosmic microwave
background data and the baryon acoustic oscillation data as well as the type Ia
supernovae data, we perform the statistic analysis to global fit these
models, finding that the logarithm parametrization and the oscillating
parametrization are almost as well as the CPL scenario in fitting these data.
We make a comparison for the impacts of the dynamical dark energy on the
cosmological constraints on the total mass of active neutrinos. We find that
the dark energy properties could significantly change the fitting results of
neutrino mass. Looser constraints on are obtained in the
logarithm and oscillating models than those derived in the CPL model.
Consideration of the possible mass ordering of neutrinos reveals that the most
stringent constraint on appears in the degenerate hierarchy
case
Anomalous Frequency Trends in MoS2 Thin Films Attributed to Surface Effects
The layered dichalcogenide MoS2 has many unique physical properties in low
dimensions. Recent experimental Raman spectroscopies report an anomalous blue
shift of the in-plane E2g1 mode with decreasing thickness, a trend that is not
understood. Here, we combine experimental Raman scattering and theoretical
studies to clarify and explain this trend. Special attention is given to
understanding the surface effect on Raman frequencies by using a force
constants model based on first-principles calculations. Surface effects refer
to the larger Mo-S force constants at the surface of thin film MoS2, which
results from a loss of neighbours in adjacent MoS2 layers. Without surface
effects, the frequencies of both out-of-plane A1g and in-plane E2g1 modes
decrease with decreasing thickness. However, the E2g1 mode blue shifts while
the A1g mode red shifts once the surface effect is included, in agreement with
the experiment. Our results show that competition between the thickness effect
and the surface effect determines the mechanical properties of two-dimensional
MoS2, which we believe applies to other layered materials
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