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"Davis, C"
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Seed filling in domesticated maize and rice depends on SWEET-mediated hexose transport
Carbohydrate import into seeds directly determines seed size and must have been increased through domestication. However, evidence of the domestication of sugar translocation and the identities of seed-filling transporters have been elusive. Maize ZmSWEET4c, as opposed to its sucrose-transporting homologs, mediates transepithelial hexose transport across the basal endosperm transfer layer (BETL), the entry point of nutrients into the seed, and shows signatures indicative of selection during domestication. Mutants of both maize ZmSWEET4c and its rice ortholog OsSWEET4 are defective in seed filling, indicating that a lack of hexose transport at the BETL impairs further transfer of sugars imported from the maternal phloem. In both maize and rice, SWEET4 was likely recruited during domestication to enhance sugar import into the endosperm.
Journal Article
Discovery of orbital-selective Cooper pairing in FeSe
The superconductor iron selenide (FeSe) is of intense interest owing to its unusual nonmagnetic nematic state and potential for high-temperature superconductivity. But its Cooper pairing mechanism has not been determined. We used Bogoliubov quasiparticle interference imaging to determine the Fermi surface geometry of the electronic bands surrounding the G = (0, 0) and X = (p/aFe, 0) points of FeSe and to measure the corresponding superconducting energy gaps. We show that both gaps are extremely anisotropic but nodeless and that they exhibit gap maxima oriented orthogonally in momentum space. Moreover, by implementing a novel technique, we demonstrate that these gaps have opposite sign with respect to each other. This complex gap configuration reveals the existence of orbital-selective Cooper pairing that, in FeSe, is based preferentially on electrons from the dyz orbitals of the iron atoms.
Journal Article
Magnetic field–induced pair density wave state in the cuprate vortex halo
High magnetic fields suppress cuprate superconductivity to reveal an unusual density wave (DW) state coexisting with unexplained quantum oscillations. Although routinely labeled a charge density wave (CDW), this DW state could actually be an electron-pair density wave (PDW). To search for evidence of a field-induced PDW, we visualized modulations in the density of electronic states N(r) within the halo surrounding Bi₂Sr₂CaCu₂O₈ vortex cores. We detected numerous phenomena predicted for a field-induced PDW, including two sets of particle-hole symmetric N(r) modulations with wave vectors QP
and 2QP
, with the latter decaying twice as rapidly from the core as the former. These data imply that the primary field-induced state in underdoped superconducting cuprates is a PDW, with approximately eight CuO₂ unit-cell periodicity and coexisting with its secondary CDWs.
Journal Article
Theatre of Nepal and the people who make it
\"Theatre of Nepal and the People Who Make It' is the first comprehensive look at Nepali theatre for readers outside of Nepal. Charting Nepali theatre from ancient times to the present and from the metropolis of Kathmandu to far-flung regions, this book highlights the history of formal theatre and connects it to shifting political and social conditions in the country. Sourcing extensive fieldwork, it takes us back stage to meet individual theatre makers and learn their unique attributes and stories. From these intimate glimpses and the intertwining of political history with theatrical expression, a portrait emerges that conveys the character of Nepalis who, in spite of adversities, continue to dramatize their hopes, fears, principles, and priorities through theatrical means\"-- Provided by publisher.
Book
Imaging orbital-selective quasiparticles in the Hund’s metal state of FeSe
Strong electronic correlations, emerging from the parent Mott insulator phase, are key to copper-based high-temperature superconductivity. By contrast, the parent phase of an iron-based high-temperature superconductor is never a correlated insulator. However, this distinction may be deceptive because Fe has five actived d orbitals while Cu has only one. In theory, such orbital multiplicity can generate a Hund’s metal state, in which alignment of the Fe spins suppresses inter-orbital fluctuations, producing orbitally selective strong correlations. The spectral weights Zm of quasiparticles associated with different Fe orbitals m should then be radically different. Here we use quasiparticle scattering interference resolved by orbital content to explore these predictions in FeSe. Signatures of strong, orbitally selective differences of quasiparticle Zm appear on all detectable bands over a wide energy range. Further, the quasiparticle interference amplitudes reveal that \\[Z_{xy} < Z_{xz} \\ll Z_{yz}\\], consistent with earlier orbital-selective Cooper pairing studies. Thus, orbital-selective strong correlations dominate the parent state of iron-based high-temperature superconductivity in FeSe.
Journal Article
A male-expressed rice embryogenic trigger redirected for asexual propagation through seeds
The molecular pathways that trigger the initiation of embryogenesis after fertilization in flowering plants, and prevent its occurrence without fertilization, are not well understood(1). Here we show in rice (Oryza sativa) that BABY BOOM1 (BBM1), a member of the AP2 family(2) of transcription factors that is expressed in sperm cells, has a key role in this process. Ectopic expression of BBM1 in the egg cell is sufficient for parthenogenesis, which indicates that a single wild-type gene can bypass the fertilization checkpoint in the female gamete. Zygotic expression of BBM1 is initially specific to the male allele but is subsequently biparental, and this is consistent with its observed auto-activation. Triple knockout of the genes BBM1, BBM2 and BBM3 causes embryo arrest and abortion, which are fully rescued by male-transmitted BBM1. These findings suggest that the requirement for fertilization in embryogenesis is mediated by male-genome transmission of pluripotency factors. When genome editing to substitute mitosis for meiosis (MiMe)(3,4) is combined with the expression of BBM1 in the egg cell, clonal progeny can be obtained that retain genome-wide parental heterozygosity. The synthetic asexual-propagation trait is heritable through multiple generations of clones. Hybrid crops provide increased yields that cannot be maintained by their progeny owing to genetic segregation. This work establishes the feasibility of asexual reproduction in crops, and could enable the maintenance of hybrids clonally through seed propagation(5,6).
Journal Article