Genomes of multicellular algal sisters to land plants illuminate signaling network evolution

Zygnematophyceae are the algal sisters of land plants. Here we sequenced four genomes of filamentous Zygnematophyceae, including chromosome-scale assemblies for three strains of Zygnema circumcarinatum. We inferred traits in the ancestor of Zygnematophyceae and land plants that might have ushered in the conquest of land by plants: expanded genes for signaling cascades, environmental response, and multicellular growth. Zygnematophyceae and land plants share all the major enzymes for cell wall synthesis and remodifications, and gene gains shaped this toolkit. Co-expression network analyses uncover gene cohorts that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution.

Three de novo assembled wild cacao genomes from the Upper Amazon

Theobroma cacao, the chocolate tree, is indigenous to the Amazon basin, the greatest biodiversity hotspot on earth. Recent advancement in plant genomics highlights the importance of de novo sequencing of multiple reference genomes to capture the genome diversity present in different cacao populations. In this study, three high-quality chromosome-level genomes of wild cacao were constructed, de novo assembled with HiFi long reads sequencing, and scaffolded using a reference-free strategy. These genomes represent the three most important genetic clusters of cacao trees from the Upper Amazon region. The three wild cacao genomes were compared with two reference genomes of domesticated cacao. The five cacao genetic clusters were inferred to have diverged in the early and middle Pleistocene period, approximately 1.83-0.69 million years ago. The results shown here serve as an example of understanding how the Amazonian biodiversity was developed. The three wild cacao genomes provide valuable resources for studying genetic diversity and advancing genetic improvement of this species.

The American Cherimoya Genome Reveals Insights into the Intra-Specific Divergence, the Evolution of Magnoliales, and a Putative Gene Cluster for Acetogenin Biosynthesis

Annona cherimola (cherimoya) is a species renowned for its delectable fruit and medicinal properties. In this study, we developed a chromosome-level genome assembly for the cherimoya 'Booth' cultivar from the United States. The genome assembly has a size of 794 Mb with a N50 = 97.59 Mb. The seven longest scaffolds account for 87.6% of the total genome length, which corresponds to the seven pseudo-chromosomes. A total of 45,272 protein-coding genes (≥30 aa) were predicted with 92.9% gene content completeness. No recent whole genome duplications were identified by an intra-genome collinearity analysis. Phylogenetic analysis supports that eudicots and magnoliids are more closely related to each other than to monocots. Moreover, the Magnoliales was found to be more closely related to the Laurales than the Piperales. Genome comparison revealed that the 'Booth' cultivar has 200 Mb less repeats than the Spanish cultivar 'Fino de Jete', despite their highly similar (>99%) genome sequence identity and collinearity. These two cultivars were diverged during the early Pleistocene (1.93 Mya), which suggests a different origin and domestication of the cherimoya. Terpene/terpenoid metabolism functions were found to be enriched in Magnoliales, while TNL (Toll/Interleukin-1-NBS-LRR) disease resistance gene has been lost in Magnoliales during evolution. We have also identified a gene cluster that is potentially responsible for the biosynthesis of acetogenins, a class of natural products found exclusively in Annonaceae. The cherimoya genome provides an invaluable resource for supporting characterization, conservation, and utilization of Annona genetic resources.

Chromosome-level genomes of multicellular algal sisters to land plants illuminate signaling network evolution

The filamentous and unicellular algae of the class Zygnematophyceae are the closest algal relatives of land plants. Inferring the properties of the last common ancestor shared by these algae and land plants allows us to identify decisive traits that enabled the conquest of land by plants. We sequenced four genomes of filamentous Zygnematophyceae (three strains of Zygnema circumcarinatum and one strain of Z. cylindricum) and generated chromosome-scale assemblies for all strains of the emerging model system Z. circumcarinatum. Comparative genomic analyses reveal expanded genes for signaling cascades, environmental response, and intracellular trafficking that we associate with multicellularity. Gene family analyses suggest that Zygnematophyceae share all the major enzymes with land plants for cell wall polysaccharide synthesis, degradation, and modifications; most of the enzymes for cell wall innovations, especially for polysaccharide backbone synthesis, were gained more than 700 million years ago. In Zygnematophyceae, these enzyme families expanded, forming co-expressed modules. Transcriptomic profiling of over 19 growth conditions combined with co-expression network analyses uncover cohorts of genes that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution.

Chromosome genome assembly for the meagre, Argyrosomus regius, reveals species adaptations and sciaenid sex-related locus evolution

The meagre, Argyrosomus regius, has recently become a species of increasing economic interest for the Mediterranean aquaculture and there is ongoing work to boost production efficiency through selective breeding. Access to the complete genomic sequence will provide an essential resource for studying quantitative trait-associated loci and exploring the genetic diversity of different wild populations and aquaculture stocks in more detail. Here, we present the first complete genome for A. regius, produced through a combination of long and short read technologies and an efficient in-house developed pipeline for assembly and polishing. Scaffolding using previous linkage map data allowed us to reconstruct a chromosome level assembly with high completeness, complemented with gene annotation and repeat masking. The 696 Mb long assembly has an N50 = 27.87 Mb and an L50 = 12, with 92.85% of its length placed in 24 chromosomes. We use this new resource to study the evolution of the meagre genome and other Sciaenids, via a comparative analysis of 25 high-quality teleost genomes. Combining a rigorous investigation of gene duplications with base-wise conservation analysis, we identify candidate loci related to immune, fat metabolism and growth adaptations in the meagre. Following phylogenomic reconstruction, we show highly conserved synteny within Sciaenidae. In contrast, we report rapidly evolving syntenic rearrangements and gene copy changes in the sex-related dmrt1 neighbourhood in meagre and other members of the family. These novel genomic datasets and findings will add important new tools for aquaculture studies and greatly facilitate husbandry and breeding work in the species.

Linkage mapping, comparative genome analysis, and QTL detection for growth in a non-model teleost, the meagre Argyrosomus regius, using ddRAD sequencing

Meagre (Argyrosomus regius), is a benthopelagic species rapidly emerging in aquaculture, due to its low food to biomass conversion rate, good fillet yield and ease of production. Tracing a species genomic background along with describing the genetic basis of important traits can greatly influence both conservation strategies and production perspectives. In this study, we employed ddRAD sequencing of 266 fish from six F1 meagre families, to construct a high-density genetic map comprising 4529 polymorphic SNP markers. The QTL mapping analysis provided a genomic appreciation for the weight trait identifying a statistically significant QTL on linkage group 15 (LG15). The comparative genomics analysis with six teleost species revealed an evolutionarily conserved karyotype structure. The synteny observed, verified the already well-known fusion events of the three-spine stickleback genome, reinforced the evidence of reduced evolutionary distance of Sciaenids with the Sparidae family, reflected the evolutionary proximity with Dicentrarchus labrax, traced several putative chromosomal rearrangements and a prominent putative fusion event in meagre’s LG17. This study presents novel elements concerning the genome evolutionary history of a non-model teleost species recently adopted in aquaculture, starts to unravel the genetic basis of the species growth-related traits, and provides a high-density genetic map as a tool that can help to further establish meagre as a valuable resource for research and production.

Metagenomic profiling of host-associated bacteria from 8 datasets of the red alga Porphyra purpurea with MetaPhlAn3

Microbial communities play fundamental roles in association with marine algae; in fact, they are recognized to be actively involved in growth and morphogenesis of the algae. Porphyra purpurea is a red alga commonly found in the intertidal zone with a high economic value, however little is known about the bacterial species associated with this genus. Here we report the bacterial-associated diversity of P. purpurea in four different localities (Ireland, Italy United Kingdom and the USA) from analyzing eight publicly available metagenomic datasets. These were analyzed with Methaplan3 to identify the putative bacterial taxonomies and their relative abundances. Furthermore, we compared these results to the 16S rRNA metagenomic analysis pipeline of the MGnify database to evaluate both methods. Kraken2 was used to verify and support the results, as a complementary classification method to Metaphlan3. This approach highlighted the different taxonomic resolution of a 16S rRNA OTU-based method compared to the pan-genome approach deployed by Metaphlan3 and complemented by Kraken2. The results presented here provide valuable preliminary data on the putative host-associated bacterial species of P. purpurea.