A chromosome-scale genome assembly of Castanopsis hystrix provides new insights into the evolution and adaptation of Fagaceae species.

Fagaceae species dominate forests and shrublands throughout the Northern Hemisphere, and have been used as models to investigate the processes and mechanisms of adaptation and speciation. Compared with the well-studied genus Quercus, genomic data is limited for the tropical-subtropical genus Castanopsis. Castanopsis hystrix is an ecologically and economically valuable species with a wide distribution in the evergreen broad-leaved forests of tropical-subtropical Asia. Here, we present a high-quality chromosome-scale reference genome of C. hystrix, obtained using a combination of Illumina and PacBio HiFi reads with Hi-C technology. The assembled genome size is 882.6 Mb with a contig N50 of 40.9 Mb and a BUSCO estimate of 99.5%, which are higher than those of recently published Fagaceae species. Genome annotation identified 37,750 protein-coding genes, of which 97.91% were functionally annotated. Repeat sequences constituted 50.95% of the genome and LTRs were the most abundant repetitive elements. Comparative genomic analysis revealed high genome synteny between C. hystrix and other Fagaceae species, despite the long divergence time between them. Considerable gene family expansion and contraction were detected in Castanopsis species. These expanded genes were involved in multiple important biological processes and molecular functions, which may have contributed to the adaptation of the genus to a tropical-subtropical climate. In summary, the genome assembly of C. hystrix provides important genomic resources for Fagaceae genomic research communities, and improves understanding of the adaptation and evolution of forest trees.

The Maternal Donor of Chrysanthemum Cultivars Revealed by Comparative Analysis of the Chloroplast Genome.

Chrysanthemum (Chrysanthemum morifolium Ramat) is an important floricultural crop and medicinal herb. Modern chrysanthemum cultivars have complex genetic backgrounds because of multiple cycles of hybridization, polyploidization, and prolonged cultivation. Understanding the genetic background and hybrid origin of modern chrysanthemum cultivars can provide pivotal information for chrysanthemum genetic improvement and breeding. By now, the origin of cultivated chrysanthemums remains unclear. In this study, 36 common chrysanthemum cultivars from across the world and multiple wild relatives were studied to identify the maternal donor of modern chrysanthemum. Chloroplast (cp) genomes of chrysanthemum cultivars were assembled and compared with those of the wild relatives. The structure of cp genomes was highly conserved among cultivars and wild relatives. Phylogenetic analyses based on the assembled cp genomes showed that all chrysanthemum cultivars grouped together and shared 64 substitutions that were distinct from those of their wild relatives. These results indicated that a diverged lineage of the genus Chrysanthemum, which was most likely an extinct or un-sampled species/population, provided a maternal source for modern cultivars. These findings provide important insights into the origin of chrysanthemum cultivars, and a source of valuable genetic markers for chrysanthemum breeding programs.

Complete chloroplast genome sequence of a Chinese traditional cultivar in Chrysanthemum, Chrysanthemum morifolium 'Anhuishiliuye'.

The complete plastid genome of Chrysanthemum morifolium 'Anhuishiliuye', a Chinese traditional cultivar, was determined and analyzed in this work. It had a circular-mapping molecular with the length of 151,059 bp.The LSC and SSC of 82,857 bp and 18,294 bp were separated by two IRs of 24,954 bp. The chloroplast genome of C. morifolium 'Anhuishiliuye' contains 125 genes, including 83 protein-coding genes, 34 ribosomal RNA genes and 8 transfer RNA genes. Phylogenetic analysis showed that C. morifolium 'Anhuishiliuye' clustered together with other Chrysanthemum species. The data provided would be useful for elucidation of phylogenetics and evolution in Chrysanthemum cultivars.

Multiferroic hydrogenated graphene bilayer.

We investigated the multiferroic properties of a hydrogenated graphene bilayer using first-principles calculations. The proposed material is composed of one fully hydrogenated and one semi-hydrogenated graphene monolayer. Inside the van der Waals gap, hydrogen atoms are only adsorbed on either the top or the bottom layer of graphene, thus breaking the centrosymmetry. The calculated electric polarization is 0.137 × 10-10 C m-1, with the transition barrier of switching the polarization being 393 meV per formula unit. We showed that ferroelectricity can be preserved down to atomic thickness. We also studied the domain wall energy and its migration for various domain wall densities, and our results indicate a robust polarization configuration against room temperature thermal fluctuation. As graphene is known to be able to sustain large strain, we further explored ferroelectricity tuning via strain, and found that the polarization can be effectively tuned up to 20% without perturbing the polarization switching barrier. Our results suggest a realizable multiferroic two-dimensional material using the most used two-dimensional material, graphene.