A genome resource for Acacia, Australia's largest plant genus

Chromosome-level de novo genome unveils the evolution of Gleditsia sinensis and thorns development

Gleditsia sinensis Lam. (G. sinensis) as an important species within the Leguminosae family, has been utilized in Chinese medicine for centuries, and its thorns serve as a chief medicinal ingredient. The absence of a comprehensive genome database has hindered its in-depth research. In this investigation, a chromosome-level de novo genome assembly of G. sinensis 'Yulin No.1' was achieved, which harbors a 786.13 Mb sized genome with 36,408 protein-coding genes and experiences two WGD events. The comparative and evolutionary analysis unveiled the close phylogenetic relationship between G. sinensis and eight other Leguminosae species. The WGCNA and gene family analysis further indicated that GsinMYB was involved in the development of thorns. This investigation offered a high-level genome of G. sinensis, facilitating comparisons in Leguminosae species evolution and functional elucidation. It also provided key insights for further research on the molecular regulation mechanisms of thorn development in plants and the molecular breeding of G. sinensis.

The genomes of seven economic Caesalpinioideae trees provide insights into polyploidization history and secondary metabolite biosynthesis

The Caesalpinioideae subfamily contains many well-known trees that are important for economic sustainability and human health, but a lack of genomic resources has hindered their breeding and utilization. Here, we present chromosome-level reference genomes for the two food and industrial trees Gleditsia sinensis (921 Mb) and Biancaea sappan (872 Mb), the three shade and ornamental trees Albizia julibrissin (705 Mb), Delonix regia (580 Mb), and Acacia confusa (566 Mb), and the two pioneer and hedgerow trees Leucaena leucocephala (1338 Mb) and Mimosa bimucronata (641 Mb). Phylogenetic inference shows that the mimosoid clade has a much higher evolutionary rate than the other clades of Caesalpinioideae. Macrosynteny comparison suggests that the fusion and breakage of an unstable chromosome are responsible for the difference in basic chromosome number (13 or 14) for Caesalpinioideae. After an ancient whole-genome duplication (WGD) shared by all Caesalpinioideae species (CWGD, ∼72.0 million years ago [MYA]), there were two recent successive WGD events, LWGD-1 (16.2-19.5 MYA) and LWGD-2 (7.1-9.5 MYA), in L. leucocephala. Thereafter, ∼40% gene loss and genome-size contraction have occurred during the diploidization process in L. leucocephala. To investigate secondary metabolites, we identified all gene copies involved in mimosine metabolism in these species and found that the abundance of mimosine biosynthesis genes in L. leucocephala largely explains its high mimosine production. We also identified the set of all potential genes involved in triterpenoid saponin biosynthesis in G. sinensis, which is more complete than that based on previous transcriptome-derived unigenes. Our results and genomic resources will facilitate biological studies of Caesalpinioideae and promote the utilization of valuable secondary metabolites.

Expression-environment associations in transcriptomic heat stress responses for a global plant lineage

The increasing frequency and severity of heatwaves will intensify stress on plants. Given regional variation in heatwave exposure and expected differences in thermal tolerance between species it is unlikely that all plant species will be affected equally by climate change. However, little is currently known about variation in the responses of plants to heat stress, or how those responses differ among closely related species adapted to different environments. Here we quantify the response of 17 Acacia species (175 RNA-seq libraries), from across Australia's diverse biomes, to a multi-day experimental heatwave treatment to identify variation in transcriptomic and physiological responses to heat stress. Genes with known heat response functions showed consistent responses across Acacia species. Up to 10% of all genes and over 100 gene families showed significant clinal variation in the magnitude of their expression plasticity across species. Specifically, gene families linked to the temperature stress response were overrepresented among significant relationships with home range temperature conditions. Gene expression responses seen on the first day of the heatwave were more frequently associated with home range climates, while expression responses by day four were more commonly related to photosystem II acclimation. Comparative transcriptomics on non-model species has the potential to provide key information on stress response plasticity, especially when linked with our understanding of model species. Our study indicates that the pressing challenge to identifying potentially vulnerable species to climate change could be benefited by the further exploration of clinal variation in transcriptome plasticity.

Plant genome information facilitates plant functional genomics

MAIN CONCLUSION

In this review, we give an overview of plant sequencing efforts and how this impacts plant functional genomics research. Plant genome sequence information greatly facilitates the studies of plant biology, functional genomics, evolution of genomes and genes, domestication processes, phylogenetic relationships, among many others. More than two decades of sequencing efforts have boosted the number of available sequenced plant genomes. The first plant genome, of Arabidopsis, was published in the year 2000 and currently, 4604 plant genomes from 1482 plant species have been published. Various large sequence initiatives are running, which are planning to produce tens of thousands of sequenced plant genomes in the near future. In this review, we give an overview on the status of sequenced plant genomes and on the use of genome information in different research areas.

Technology-enabled great leap in deciphering plant genomes

Plant genomes provide essential and vital basic resources for studying many aspects of plant biology and applications (for example, breeding). From 2000 to 2020, 1,144 genomes of 782 plant species were sequenced. In the past three years (2021-2023), 2,373 genomes of 1,031 plant species, including 793 newly sequenced species, have been assembled, representing a great leap. The 2,373 newly assembled genomes, of which 63 are telomere-to-telomere assemblies and 921 have been generated in pan-genome projects, cover the major phylogenetic clades. Substantial advances in read length, throughput, accuracy and cost-effectiveness have notably simplified the achievement of high-quality assemblies. Moreover, the development of multiple software tools using different algorithms offers the opportunity to generate more complete and complex assemblies. A database named N3: plants, genomes, technologies has been developed to accommodate the metadata associated with the 3,517 genomes that have been sequenced from 1,575 plant species since 2000. We also provide an outlook for emerging opportunities in plant genome sequencing.

Chromosome-level genome of the transformable northern wattle, Acacia crassicarpa

The genus Acacia is a large group of woody legumes containing an enormous amount of morphological diversity in leaf shape. This diversity is at least in part the result of an innovation in leaf development where many Acacia species are capable of developing leaves of both bifacial and unifacial morphologies. While not unique in the plant kingdom, unifaciality is most commonly associated with monocots, and its developmental genetic mechanisms have yet to be explored beyond this group. In this study, we identify an accession of Acacia crassicarpa with high regeneration rates and isolate a clone for genome sequencing. We generate a chromosome-level assembly of this readily transformable clone, and using comparative analyses, confirm a whole-genome duplication unique to Caesalpinoid legumes. This resource will be important for future work examining genome evolution in legumes and the unique developmental genetic mechanisms underlying unifacial morphogenesis in Acacia.