Genome size (also known as the C-value) refers to the total amount of DNA contained within one copy of a single complete genome; it is broadly constant within an organism (Greilhuber et al., 2005; Swift, 1950). More and more species' genome sizes have been assessed since early studies in the 1950s, covering more than 12,273

Background Eudicots are the most diverse group of flowering plants that compromise five well-defined lineages: core eudicots, Ranunculales, Proteales, Trochodendrales, and Buxales. However, the phylogenetic relationships between these five lineages and their chromosomal evolutions remain unclear, and a lack of high-quality genome analyses for Buxales has hindered many efforts to address this knowledge gap. Results Here, we present a high-quality chromosome-level genome of Buxus austro-yunnanensis (Buxales). Our phylogenomic analyses revealed that Buxales and Trochodendrales are genetically similar and classified as sisters. Additionally, both are sisters to the core eudicots, while Ranunculales was found to be the first lineage to diverge from these groups. Incomplete lineage sorting and hybridization were identified as the main contributors to phylogenetic discordance (34.33%) between the lineages. In fact, B. austro-yunnanensis underwent only one whole-genome duplication event, and collinear gene phylogeny analyses suggested that separate independent polyploidizations occurred in the five eudicot lineages. Using representative genomes from these five lineages, we reconstructed the ancestral eudicot karyotype (AEK) and generated a nearly gapless karyotype projection for each eudicot species. Within core eudicots, we recovered one common chromosome fusion event in asterids and malvids, respectively. Further, we also found that the previously reported fused AEKs in Aquilegia (Ranunculales) and Vitis (core eudicots) have different fusion positions, which indicates that these two species have different karyotype evolution histories. Conclusions Based on our phylogenomic and karyotype evolution analyses, we revealed the likely relationships and evolutionary histories of early eudicots. Ultimately, our study expands genomic resources for early-diverging eudicots.

Background Bretschneidera sinensis is an endangered relic tree species in the Akaniaceae family and is sporadically distributed in eastern Asia. As opposed to its current narrow and rare distribution, the fossil pollen of B. sinensis has been found to be frequent and widespread in the Northern Hemisphere during the Late Miocene. B. sinensis is also a typical mycorrhizal plant, and its annual seedlings exhibit high mortality rates in absence of mycorrhizal development. The chromosome-level high-quality genome of B. sinensis will help us to more deeply understand the survival and demographic histories of this relic species. Results A total of 25.39 Gb HiFi reads and 109.17 Gb Hi-C reads were used to construct the chromosome-level genome of B. sinensis, which is 1.21 Gb in length with the contig N50 of 64.13 Mb and chromosome N50 of 146.54 Mb. The identified transposable elements account for 55.21% of the genome. A total of 45,839 protein-coding genes were predicted in B. sinensis. A lineage-specific whole-genome duplication was detected, and 7,283 lineage-specific expanded gene families with functions related to the specialized endotrophic mycorrhizal adaptation were identified. The historical effective population size (Ne) of B. sinensis was found to oscillate greatly in response to Quaternary climatic changes. The Ne of B. sinensis has decreased rapidly in the recent past, making its extant Ne extremely lower. Our additional evolutionary genomic analyses suggested that the developed mycorrhizal adaption might have been repeatedly disrupted by environmental changes caused by Quaternary climatic oscillations. The environmental changes and an already decreased population size during the Holocene may have led to the current rarity of B. sinensis. Conclusion This is a detailed report of the genome sequences for the family Akaniaceae distributed in evergreen forests in eastern Asia. Such a high-quality genomic resource may provide critical clues for comparative genomics studies of this family in the future.

Flowering plants (angiosperms) dominate our planet and sustain all life on Earth. However, evolutionary relationships among the angiosperm lineages that diverged early – Amborellales, Nymphaeales, Austrobaileyales and Mesangiospermae, which further comprises monocots and other four clades – have remained highly disputed likely because of their rapid diversification promoted by an ancestral polyploidization event. Here, we present high-quality chromosomal-level genome assemblies of two species – star anise (Illicium verum: 12.5 Gb with a large size) in the Austrobaileyales and calamus (Acorus gramineus) representing the sister lineage to all other extant monocots. These two genomes filled the final gaps of all genomic representatives for major angiosperm lineages. Our phylogenetic analyses of collinear genes support Amborellales and Nymphaeales as sister lineages and they, together with Austrobaileyales and monocots are successively sister to other Mesangiospermae clades. Based on chromosome-like synteny blocks shared between extant genomes, we constructed the ancestral angiosperm karyotype to be x=16. We independently established evolutionary relationships for all sampled species based on shared polyploidizations and chromosomal fusions from the common ancestral karyotype. This phylogenetic relationship is congruent with that from collinear genes, especially the finding that Amborellales and Nymphaeales shared a rare chromosomal fusion not seen in other angiosperms. These results advance our understanding and shed new lights on early diversification and karyotype evolution of flowering plants.

Objectives: Toward common methods for system monitoring and evaluation, we proposed a key performance indicator framework and discussed lessons learned while implementing a statewide exposure notification (EN) system in California during the COVID-19 epidemic. Materials and Methods: California deployed the Google Apple Exposure Notification framework, branded CA Notify, on December 10, 2020, to supplement traditional COVID-19 contact tracing programs. For system evaluation, we defined 6 key performance indicators: adoption, retention, sharing of unique codes, identification of potential contacts, behavior change, and impact. We aggregated and analyzed data from December 10, 2020, to July 1, 2021, in compliance with the CA Notify privacy policy. Results: We estimated CA Notify adoption at nearly 11 million smartphone activations during the study period. Among 1 654 201 CA Notify users who received a positive test result for SARS-CoV-2, 446 634 (27%) shared their unique code, leading to ENs for other CA Notify users who were in close proximity to the SARS-CoV-2–positive individual. We identified at least 122 970 CA Notify users as contacts through this process. Contact identification occurred a median of 4 days after symptom onset or specimen collection date of the user who received a positive test result for SARS-CoV-2. Practice Implications: Smartphone-based EN systems are promising new tools to supplement traditional contact tracing and public health interventions, particularly when efficient scaling is not feasible for other approaches. Methods to collect and interpret appropriate measures of system performance must be refined while maintaining trust and privacy.