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The gymnosperm Welwitschia mirabilis belongs to the ancient, enigmatic gnetophyte lineage. It is a unique desert plant with extreme longevity and two ever-elongating leaves. We present a chromosome-level assembly of its genome (6.8 Gb/1 C) together with methylome and transcriptome data to explore its astonishing biology. We also present a refined, high-quality assembly of Gnetum montanum to enhance our understanding of gnetophyte genome evolution. The Welwitschia genome has been shaped by a lineage-specific ancient, whole genome duplication (~86 million years ago) and more recently (1-2 million years) by bursts of retrotransposon activity. High levels of cytosine methylation (particularly at CHH motifs) are associated with retrotransposons, whilst long-term deamination has resulted in an exceptionally GC-poor genome. Changes in copy number and/or expression of gene families and transcription factors (e.g. R2R3MYB, SAUR) controlling cell growth, differentiation and metabolism underpin the plant’s longevity and tolerance to temperature, nutrient and water stress.

Gnetum (Gnetales: Gnetaceae) constitutes an evolutionarily isolated gymnosperm clade, comprising about 40 species that inhabit tropical areas of the world. While its closest living relative, the monotypic Welwitschia, has a well-documented fossil record from the Early Cretaceous, Gnetum-like fossils are rare and poorly understood. The phylogeny of Gnetum has been studied previously but the distant relationship to outgroups and the difficulty of obtaining plant material mean it is not yet fully resolved. Most species are tropical lianas with an angiospermous vegetative habit that are difficult to find and identify. Here a new phylogeny is presented based on nuclear and chloroplast data from 58 Gnetum accessions, representing 27 putative species, and outgroup information from other seed plants. The results provide support for South American species being sister to the remaining species. The two African species constitute a monophyletic group, sister to an Asian clade, within which the two arborescent species of the genus are the earliest diverging. Estimated divergence times indicate, in contrast with previous results, that the major lineages of Gnetum diverged in the Late Cretaceous. This result is obtained regardless of tree prior used in the BEAST analyses (Yule or birth-death). Together these findings suggest a correlation between early divergence events in extant Gnetum and the breakup of Gondwana in the Cretaceous. Compared to the old stem ages of major subclades of Gnetum, crown nodes date to the Cenozoic: the Asian crown group dates to the Cretaceous-Paleogene (K-Pg) boundary, the African crown group to the mid-Paleogene, and the South American crown group to the Paleogene-Neogene boundary. Although dispersal must have contributed to the current distribution of Gnetum, e.g., within South America and from Southeast Asian islands to the East Asian mainland, dispersal has apparently not occurred across major oceans, at least not during the Cenozoic.

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The genus Gnetum includes pantropical trees, shrubs and lianas, with unresolved phylogenetic relationships with other seed plant groups. Despite the reference genome for this genus being recently published, the molecular mechanisms that regulate the reproductive organ development of Gnetum remain unclear. A previous study showed that indole-3-acetic acid is involved in the regulation of female strobili of Gnetum, while the diversity and evolution of indole-3-acetic acid-related genes—the Aux/IAA genes—have never been investigated in Gnetales. Thus, a pooled sample from different developmental stages of female strobili in Gnetum luofuense C.Y. Cheng was sequenced using PacBio single-molecular long-read technology (SMRT) sequencing. PacBio SMRT sequencing generated a total of 53,057 full-length transcripts, including 2043 novel genes. Besides this, 10,454 alternative splicing (AS) events were detected with intron retention constituting the largest proportion (46%). Moreover, 1196 lncRNAs were identified, and 8128 genes were found to possess at least one poly (A) site. A total of 3179 regulatory proteins, including 1413 transcription factors (e.g., MADS-box and bHLHs), 477 transcription regulators (e.g., SNF2), and 1289 protein kinases (e.g., RLK/Pelles) were detected, and these protein regulators probably participated in the female strobili development of G. luofuense. In addition, this is the first study of the Aux/IAA genes of the Gnetales, and we identified 6, 7 and 12 Aux/IAA genes from Gnetum luofuense, Welwitschia mirabilis, and Ephedra equistina, respectively. Our phylogenetic analysis reveals that Aux/IAA genes from the gymnosperms tended to cluster and possessed gene structures as diverse as those in angiosperms. Moreover, the Aux/IAA genes of the Gnetales might possess higher molecular evolutionary rates than those in other gymnosperms. The sequencing of the full-length transcriptome paves the way to uncovering molecular mechanisms that regulate reproductive organ development in gymnosperms.

SEI films directly affect the dissolution and deposition of lithium during discharge and charge and thus are one of the key factors that determine the safety, power capability, morphology of lithium deposits, shelf life, and cycle life of LIBs. In particular, the breakdown of SEI can result in the nucleation and growth of lithium dendrites and cause the safety risk for the practical applications of LIBs in the electric vehicles and other high-energy-density electronic devices. [5,6] While, a stable and robust SEI film can effectively inhibit the lithium dendrite growth and thus prominently enhance the cycling performance and safety of the batteries. [1,7] Owing to directly growing on anode surfaces, the formation and stability of SEI films are greatly influenced by the volume variation of anodes during the charge-discharge cycling, especially at a high current density. [1,8] Although the importance of SEI has been widely recognized, the structure and kinetics of SEI are the less wellunderstood phenomena impacting battery technology. Various in situ techniques, for instances, in situ spectroscopic ellipsometry, [9] in situ nuclear magnetic resonance (NMR), [10] in situ X-ray diffraction, [11] in situ Fourier transform infrared (FTIR) spectroscopy, [12] and in situ electrochemical impedance spectroscopy, [13] have been employed to investigate the evolution of SEI films. Nevertheless, most of them are limited to the nonintuitive investigations. Several key questions on the SEI film formation, structure and failure are still elusive.Recently, in situ transmission electron microscopy (TEM) has been utilized as a power tool to explore the evolution of SEI films in LIBs. In particular, a liquid cell TEM technique can well mimic the chemical and electrochemical reactions in liquid media with controllable charge and discharge conditions of LIBs. Sacci et al. performed the first in situ TEM observations of SEI film formation on a gold electrode during cyclic voltammetry testing. [14] They found that SEI films form heterogeneously on the gold electrode and possess dendritic morphology. The formation and growth of SEI films on graphite/electrolyte interfaces were studied by Unocic et al. using in situ TEM. [15] By utilizing the liquid cell TEM, Zeng et al. monitored the structural evolution of SEI films in a cyclic voltammetry process and found that the growth of SEI films is limited by the electron transport and produces gaseous The solid electrolyte interphase (SEI) spontaneously formed on anode surfaces as a passivation layer plays a critical role in the lithium dissolution and deposition upon discharge/charge in lithium ion batteries and lithiummetal batteries. The formation kinetics and failure of the SEI films are the key factors determining the safety, power capability, and cycle life of lithium ion and lithium-metal batteries. Since SEI films evolve with the volumetric and interfacial changes of anodes, it is technically challenging in experimental study of SEI kinetics. Here operando observations are reported of SEI...

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