Resolution of Brassicaceae Phylogeny Using Nuclear Genes Uncovers Nested Radiations and Supports Convergent Morphological Evolution

Genomes of Meniocus linifolius and Tetracme quadricornis reveal the ancestral karyotype and genomic features of core Brassicaceae

Brassicaceae represents an important plant family from both a scientific and economic perspective. However, genomic features related to the early diversification of this family have not been fully characterized, especially upon the uplift of the Tibetan Plateau, which was followed by increasing aridity in the Asian interior, intensifying monsoons in Eastern Asia, and significantly fluctuating daily temperatures. Here, we reveal the genomic architecture that accompanied early Brassicaceae diversification by analyzing two high-quality chromosome-level genomes for Meniocus linifolius (Arabodae; clade D) and Tetracme quadricornis (Hesperodae; clade E), together with genomes representing all major Brassicaceae clades and the basal Aethionemeae. We reconstructed an ancestral core Brassicaceae karyotype (CBK) containing 9 pseudochromosomes with 65 conserved syntenic genomic blocks and identified 9702 conserved genes in Brassicaceae. We detected pervasive conflicting phylogenomic signals accompanied by widespread ancient hybridization events, which correlate well with the early divergence of core Brassicaceae. We identified a successive Brassicaceae-specific expansion of the class I TREHALOSE-6-PHOSPHATE SYNTHASE 1 (TPS1) gene family, which encodes enzymes with essential regulatory roles in flowering time and embryo development. The TPS1s were mainly randomly amplified, followed by expression divergence. Our results provide fresh insights into historical genomic features coupled with Brassicaceae evolution and offer a potential model for broad-scale studies of adaptive radiation under an ever-changing environment.

Nuclear phylogenomics of Asteraceae with increased sampling provides new insights into convergent morphological and molecular evolution

Convergent morphological evolution is widespread in flowering plants, and understanding this phenomenon relies on well-resolved phylogenies. Nuclear phylogenetic reconstruction using transcriptome datasets has been successful in various angiosperm groups, but it is limited to taxa with available fresh materials. Asteraceae, which are one of the two largest angiosperm families and are important for both ecosystems and human livelihood, show multiple examples of convergent evolution. Nuclear Asteraceae phylogenies have resolved relationships among most subfamilies and many tribes, but many phylogenetic and evolutionary questions regarding subtribes and genera remain, owing to limited sampling. Here, we increased the sampling for Asteraceae phylogenetic reconstruction using transcriptomes and genome-skimming datasets and produced nuclear phylogenetic trees with 706 species representing two-thirds of recognized subtribes. Ancestral character reconstruction supports multiple convergent evolutionary events in Asteraceae, with gains and losses of bilateral floral symmetry correlated with diversification of some subfamilies and smaller groups, respectively. Presence of the calyx-related pappus may have been especially important for the success of some subtribes and genera. Molecular evolutionary analyses support the likely contribution of duplications of MADS-box and TCP floral regulatory genes to innovations in floral morphology, including capitulum inflorescences and bilaterally symmetric flowers, potentially promoting the diversification of Asteraceae. Subsequent divergences and reductions in CYC2 gene expression are related to the gain and loss of zygomorphic flowers. This phylogenomic work with greater taxon sampling through inclusion of genome-skimming datasets reveals the feasibility of expanded evolutionary analyses using DNA samples for understanding convergent evolution.

The chromosome-level genomes of the herbal magnoliids Warburgia ugandensis and Saururus chinensis

Warburgia ugandensis and Saururus chinensis are two of the most important medicinal plants in magnoliids and are widely utilized in traditional Kenya and Chinese medicine, respectively. The absence of higher-quality reference genomes has hindered research on the medicinal compound biosynthesis mechanisms of these plants. We report the chromosome-level genome assemblies of W. ugandensis and S. chinensis, and generated 1.13 Gb and 0.53 Gb genomes from 74 and 27 scaffolds, respectively, using BGI-DIPSEQ, Nanopore, and Hi-C sequencing. The scaffold N50 lengths were 82.97 Mb and 48.53 Mb, and the assemblies were anchored to 14 and 11 chromosomes of W. ugandensis and S. chinensis, respectively. In total, 24,739 and 20,561 genes were annotated, and 98.5% and 98% of the BUSCO genes were fully represented, respectively. The chromosome-level genomes of W. ugandensis and S. chinensis will be valuable resources for understanding the genetics of these medicinal plants, studying the evolution of magnoliids and angiosperms and conserving plant genetic resources.

Complementing model species with model clades

Model species continue to underpin groundbreaking plant science research. At the same time, the phylogenetic resolution of the land plant tree of life continues to improve. The intersection of these 2 research paths creates a unique opportunity to further extend the usefulness of model species across larger taxonomic groups. Here we promote the utility of the Arabidopsis thaliana model species, especially the ability to connect its genetic and functional resources, to species across the entire Brassicales order. We focus on the utility of using genomics and phylogenomics to bridge the evolution and diversification of several traits across the Brassicales to the resources in Arabidopsis, thereby extending scope from a model species by establishing a "model clade." These Brassicales-wide traits are discussed in the context of both the model species Arabidopsis and the family Brassicaceae. We promote the utility of such a "model clade" and make suggestions for building global networks to support future studies in the model order Brassicales.

A chromosome-level genome assembly for the amphibious plant Rorippa aquatica reveals its allotetraploid origin and mechanisms of heterophylly upon submergence

The ability to respond to varying environments is crucial for sessile organisms such as plants. The amphibious plant Rorippa aquatica exhibits a striking type of phenotypic plasticity known as heterophylly, a phenomenon in which leaf form is altered in response to environmental factors. However, the underlying molecular mechanisms of heterophylly are yet to be fully understood. To uncover the genetic basis and analyze the evolutionary processes driving heterophylly in R. aquatica, we assembled the chromosome-level genome of the species. Comparative chromosome painting and chromosomal genomics revealed that allopolyploidization and subsequent post-polyploid descending dysploidy occurred during the speciation of R. aquatica. Based on the obtained genomic data, the transcriptome analyses revealed that ethylene signaling plays a central role in regulating heterophylly under submerged conditions, with blue light signaling acting as an attenuator of ethylene signal. The assembled R. aquatica reference genome provides insights into the molecular mechanisms and evolution of heterophylly.

Nuclear phylogenomics of angiosperms and insights into their relationships and evolution

Angiosperms (flowering plants) are by far the most diverse land plant group with over 300,000 species. The sudden appearance of diverse angiosperms in the fossil record was referred to by Darwin as the "abominable mystery," hence contributing to the heightened interest in angiosperm evolution. Angiosperms display wide ranges of morphological, physiological, and ecological characters, some of which have probably influenced their species richness. The evolutionary analyses of these characteristics help to address questions of angiosperm diversification and require well resolved phylogeny. Following the great successes of phylogenetic analyses using plastid sequences, dozens to thousands of nuclear genes from next-generation sequencing have been used in angiosperm phylogenomic analyses, providing well resolved phylogenies and new insights into the evolution of angiosperms. In this review we focus on recent nuclear phylogenomic analyses of large angiosperm clades, orders, families, and subdivisions of some families and provide a summarized Nuclear Phylogenetic Tree of Angiosperm Families. The newly established nuclear phylogenetic relationships are highlighted and compared with previous phylogenetic results. The sequenced genomes of Amborella, Nymphaea, Chloranthus, Ceratophyllum, and species of monocots, Magnoliids, and basal eudicots, have facilitated the phylogenomics of relationships among five major angiosperms clades. All but one of the 64 angiosperm orders were included in nuclear phylogenomics with well resolved relationships except the placements of several orders. Most families have been included with robust and highly supported placements, especially for relationships within several large and important orders and families. Additionally, we examine the divergence time estimation and biogeographic analyses of angiosperm on the basis of the nuclear phylogenomic frameworks and discuss the differences compared with previous analyses. Furthermore, we discuss the implications of nuclear phylogenomic analyses on ancestral reconstruction of morphological, physiological, and ecological characters of angiosperm groups, limitations of current nuclear phylogenomic studies, and the taxa that require future attention.

The evolution of ephemeral flora in Xinjiang, China: insights from plastid phylogenomic analyses of Brassicaceae

BACKGROUND

The ephemeral flora of northern Xinjiang, China, plays an important role in the desert ecosystems. However, the evolutionary history of this flora remains unclear. To gain new insights into its origin and evolutionary dynamics, we comprehensively sampled ephemeral plants of Brassicaceae, one of the essential plant groups of the ephemeral flora.

RESULTS

We reconstructed a phylogenetic tree using plastid genomes and estimated their divergence times. Our results indicate that ephemeral species began to colonize the arid areas in north Xinjiang during the Early Miocene and there was a greater dispersal of ephemeral species from the surrounding areas into the ephemeral community of north Xinjiang during the Middle and Late Miocene, in contrast to the Early Miocene or Pliocene periods.

CONCLUSIONS

Our findings, together with previous studies, suggest that the ephemeral flora originated in the Early Miocene, and species assembly became rapid from the Middle Miocene onwards, possibly attributable to global climate changes and regional geological events.

Angiosperm-wide analysis of fruit and ovary evolution aided by a new nuclear phylogeny supports association of the same ovary type with both dry and fleshy fruits

Fruit functions in seed protection and dispersal and belongs to many dry and fleshy types, yet their evolutionary pattern remains unclear in part due to uncertainties in the phylogenetic relationships among several orders and families. Thus we used nuclear genes of 502 angiosperm species representing 231 families to reconstruct a well supported phylogeny, with resolved relationships for orders and families with previously uncertain placements. Using this phylogeny as a framework, molecular dating supports a Triassic origin of the crown angiosperms, followed by the emergence of most orders in the Jurassic and Cretaceous and their rise to ecological dominance during the Cretaceous Terrestrial Revolution. The robust phylogeny allowed an examination of the evolutionary pattern of fruit and ovary types, revealing a trend of parallel carpel fusions during early diversifications in eudicots, monocots, and magnoliids. Moreover, taxa in the same order or family with the same ovary type can develop either dry or fleshy fruits with strong correlations between specific types of dry and fleshy fruits; such associations of ovary, dry and fleshy fruits define several ovary-fruit "modules" each found in multiple families. One of the frequent modules has an ovary containing multiple ovules, capsules and berries, and another with an ovary having one or two ovules, achenes (or other single-seeded dry fruits) and drupes. This new perspective of relationships among fruit types highlights the closeness of specific dry and fleshy fruit types, such as capsule and berry, that develop from the same ovary type and belong to the same module relative to dry and fleshy fruits of other modules (such as achenes and drupes). Further analyses of gene families containing known genes for ovary and fruit development identified phylogenetic nodes with multiple gene duplications, supporting a possible role of whole-genome duplications, in combination with climate changes and animal behaviors, in angiosperm fruit and ovary diversification.

Research progress on Brassicaceae plants: a bibliometrics analysis

The Brassicaceae is a worldwide family that produces ornamental flowers, edible vegetables, and oilseed plants, with high economic value in agriculture, horticulture, and landscaping. This study used the Web of Science core dataset and the CiteSpace bibliometric tool to quantitatively visualize the number of publications, authors, institutions, and countries of 3139 papers related to Brassicaceae plants from 2002 to 2022. The keywords and references were divided into two phases: Phase 1 (2002-2011) and Phase 2 (2012-2022) for quantitative and qualitative analysis. The results showed: An average annual publication volume of 149 articles, with an overall fluctuating upward trend; the research force was mainly led by Professor Ihsan A. Al-shehbaz from Missouri Botanical Garden; and the United States had the highest number of publications. In the first phase, research focused on the phylogeny of Brassicaceae plants, while the second phase delved into diverse research based on previous studies, research in areas such as polyploidy, molecular technique, physiology, and hyperaccumulator has been extended. Based on this research, we propounded some ideas for future studies on Brassicaceae plants and summarized the research gaps.

Remarkable mitochondrial genome heterogeneity in Meniocus linifolius (Brassicaceae)

KEY MESSAGE

Detailed analyses of 16 genomes identified a remarkable acceleration of mutation rate, hence mitochondrial sequence and structural heterogeneity, in Meniocus linifolius (Brassicaceae). The powerhouse, mitochondria, in plants feature high levels of structural variation, while the encoded genes are normally conserved. However, the substitution rates and spectra of mitochondria DNA within the Brassicaceae, a family with substantial scientific and economic importance, have not been adequately deciphered. Here, by analyzing three newly assembled and 13 known mitochondrial genomes (mitogenomes), we report the highly variable genome structure and mutation rates in Brassicaceae. The genome sizes and GC contents are 196,604 bp and 46.83%, 288,122 bp and 44.79%, and 287,054 bp and 44.93%, for Meniocus linifolius (Mli), Crucihimalaya lasiocarpa (Cla), and Lepidium sativum (Lsa), respectively. In total, 29, 33, and 34 protein-coding genes (PCGs) and 14, 18, and 18 tRNAs are annotated for Mli, Cla, and Lsa, respectively, while all mitogenomes contain one complete circular molecule with three rRNAs and abundant RNA editing sites. The Mli mitogenome features four conformations likely mediated by the two pairs of long repeats, while at the same time seems to have an unusual evolutionary history due to higher GC content, loss of more genes and sequences, but having more repeats and plastid DNA insertions. Corroborating with these, an ambiguous phylogenetic position with long branch length and elevated synonymous substitution rate in nearly all PCGs are observed for Mli. Taken together, our results reveal a high level of mitogenome heterogeneity at the family level and provide valuable resources for further understanding the evolutionary pattern of organelle genomes in Brassicaceae.

Genomic exploration of Sesuvium sesuvioides: comparative study and phylogenetic analysis within the order Caryophyllales from Cholistan desert, Pakistan

BACKGROUND

The Aizoaceae family's Sesuvium sesuvioides (Fenzl) Verdc is a medicinal species of the Cholistan desert, Pakistan. The purpose of this study was to determine the genomic features and phylogenetic position of the Sesuvium genus in the Aizoaceae family. We used the Illumina HiSeq2500 and paired-end sequencing to publish the complete chloroplast sequence of S. sesuvioides.

RESULTS

The 155,849 bp length cp genome sequence of S. sesuvioides has a 36.8% GC content. The Leucine codon has the greatest codon use (10.6%), 81 simple sequence repetitions of 19 kinds, and 79 oligonucleotide repeats. We investigated the phylogeny of the order Caryophyllales' 27 species from 23 families and 25 distinct genera. The maximum likelihood tree indicated Sesuvium as a monophyletic genus, and sister to Tetragonia. A comparison of S. sesuvioides, with Sesuvium portulacastrum, Mesembryanthemum crystallinum, Mesembryanthemum cordifolium, and Tetragonia tetragonoides was performed using the NCBI platform. In the comparative investigation of genomes, all five genera revealed comparable cp genome structure, gene number and composition. All five species lacked the rps15 gene and the rpl2 intron. In most comparisons with S. sesuvioides, transition substitutions (Ts) were more frequent than transversion substitutions (Tv), producing Ts/Tv ratios larger than one, and the Ka/Ks ratio was lower than one. We determined ten highly polymorphic regions, comprising rpl22, rpl32-trnL-UAG, trnD-GUC-trnY-GUA, trnE-UUC-trnT-GGU, trnK-UUU-rps16, trnM-CAU-atpE, trnH-GUG-psbA, psaJ-rpl33, rps4-trnT-UGU, and trnF-GAA-ndhJ.

CONCLUSION

The whole S. sesuvioides chloroplast will be examined as a resource for in-depth taxonomic research of the genus when more Sesuvium and Aizoaceae species are sequenced in the future. The chloroplast genomes of the Aizoaceae family are well preserved, with little alterations, indicating the family's monophyletic origin. This study's highly polymorphic regions could be utilized to build realistic and low-cost molecular markers for resolving taxonomic discrepancies, new species identification, and finding evolutionary links among Aizoaceae species. To properly comprehend the evolution of the Aizoaceae family, further species need to be sequenced.

Phylotranscriptomic analyses reveal deep gene tree discordance in Camellia (Theaceae)

Gene tree discordance is a significant legacy of biological evolution. Multiple factors can result in incongruence among genes, such as introgression, incomplete lineage sorting (ILS), gene duplication or loss. Resolving the background of gene tree discordance is a critical way to uncover the process of species diversification. Camellia, the largest genus in Theaceae, has controversial taxonomy and systematics due in part to a complex evolutionary history. We used 60 transcriptomes of 55 species, which represented 15 sections of Camellia to investigate its phylogeny and the possible causes of gene tree discordance. We conducted gene tree discordance analysis based on 1,617 orthologous low-copy nuclear genes, primarily using coalescent species trees and polytomy tests to distinguish hard and soft conflict. A selective pressure analysis was also performed to assess the impact of selection on phylogenetic topology reconstruction. Our results detected different levels of gene tree discordance in the backbone of Camellia, and recovered rapid diversification as one of the possible causes of gene tree discordance. Furthermore, we confirmed that none of the currently proposed sections of Camellia was monophyletic. Comparisons among datasets partitioned under different selective pressure regimes showed that integrating all orthologous genes provided the best phylogenetic resolution of the species tree of Camellia. The findings of this study reveal rapid diversification as a major source of gene tree discordance in Camellia and will facilitate future investigation of reticulate relationships at the species level in this important plant genus.

A genomic panel for studying C3-C4 intermediate photosynthesis in the Brassiceae tribe

Research on C4 and C3-C4 photosynthesis has attracted significant attention because the understanding of the genetic underpinnings of these traits will support the introduction of its characteristics into commercially relevant crop species. We used a panel of 19 taxa of 18 Brassiceae species with different photosynthesis characteristics (C3 and C3-C4) with the following objectives: (i) create draft genome assemblies and annotations, (ii) quantify orthology levels using synteny maps between all pairs of taxa, (iii) ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠describe the phylogenetic relatedness across all the species, and (iv) track the evolution of C3-C4 intermediate photosynthesis in the Brassiceae tribe. Our results indicate that the draft de novo genome assemblies are of high quality and cover at least 90% of the gene space. Therewith we more than doubled the sampling depth of genomes of the Brassiceae tribe that comprises commercially important as well as biologically interesting species. The gene annotation generated high-quality gene models, and for most genes extensive upstream sequences are available for all taxa, yielding potential to explore variants in regulatory sequences. The genome-based phylogenetic tree of the Brassiceae contained two main clades and indicated that the C3-C4 intermediate photosynthesis has evolved five times independently. Furthermore, our study provides the first genomic support of the hypothesis that Diplotaxis muralis is a natural hybrid of D. tenuifolia and D. viminea. Altogether, the de novo genome assemblies and the annotations reported in this study are a valuable resource for research on the evolution of C3-C4 intermediate photosynthesis.

Antagonistic RALF peptides control an intergeneric hybridization barrier on Brassicaceae stigmas

Pollen-pistil interactions establish interspecific/intergeneric pre-zygotic hybridization barriers in plants. The rejection of undesired pollen at the stigma is crucial to avoid outcrossing but can be overcome with the support of mentor pollen. The mechanisms underlying this hybridization barrier are largely unknown. Here, in Arabidopsis, we demonstrate that receptor-like kinases FERONIA/CURVY1/ANJEA/HERCULES RECEPTOR KINASE 1 and cell wall proteins LRX3/4/5 interact on papilla cell surfaces with autocrine stigmatic RALF1/22/23/33 peptide ligands (sRALFs) to establish a lock that blocks the penetration of undesired pollen tubes. Compatible pollen-derived RALF10/11/12/13/25/26/30 peptides (pRALFs) act as a key, outcompeting sRALFs and enabling pollen tube penetration. By treating Arabidopsis stigmas with synthetic pRALFs, we unlock the barrier, facilitating pollen tube penetration from distantly related Brassicaceae species and resulting in interspecific/intergeneric hybrid embryo formation. Therefore, we uncover a "lock-and-key" system governing the hybridization breadth of interspecific/intergeneric crosses in Brassicaceae. Manipulating this system holds promise for facilitating broad hybridization in crops.

Complex origin, evolution, and diversification of non-canonically organized OVATE-OFP and OVATE-Like OFP gene pair across Embryophyta

Ovate Family Proteins (OFP) is a plant-specific gene family of negative transcriptional regulators. Till-date, a handful of in-silico studies have provided glimpses into family size, expansion patterns, and genic features across all major plant lineages. A major lacuna exists in understanding origin of organisation complexity of members such as those arranged in a head-to-head manner which may lead to transcriptional co-regulation via a common bi-directional promoter. To address this gap, we investigated the origin, organization and evolution of two head-to-head arranged gene pairs of homologs of AtOFP2-AtOFP17, and, AtOFP4-AtOFP20 across Archaeplastida. The ancestral forms of AtOFP2, AtOFP4, AtOFP17, and AtOFP20 are likely to have evolved in last common ancestors of Embryophyta (land plants) given their complete absence in Rhodophyta and Chlorophyta. The OFP gene family originated and expanded in Bryophyta, including protein variants with complete (OVATE-OFP) or partial (OVATE-Like OFP) OVATE domain; with head-to-head organization present only in Spermatophyta (gymnosperms and angiosperms). Ancestral State Reconstruction revealed the origin of head-to-head organized gene pair in gymnosperms, with both genes being OVATE-OFP (homologs of AtOFP2/4). Phylogenetic reconstruction and copy number analysis suggests the presence of a single copy of the head-to-head arranged pair of OFP2/4 (OVATE)-OFP17/20 (OVATE-Like) in all angiosperms except Brassicaceae, and a duplication event in last common ancestor of core Brassicaceae approximately 32-54 MYA leading to origin of AtOFP2-AtOFP17 and AtOFP4-AtOFP20 as paralogs. Synteny analysis of genomic regions harbouring homologs of AtOFP2-AtOFP17, AtOFP4-AtOFP20 and AtOFP2/4-AtOFP17/20 across angiosperms suggested ancestral nature of AtOFP2-AtOFP17 gene pair. The present study thus establishes the orthology and evolutionary history of two non-canonically organised gene pairs with variation in their OVATE domain. The non-canonical organisation, atleast in Brassicaceae, has the potential of generating complex transcriptional regulation mediated via a common bi-directional promoter. The study thus lays down a framework to understand evolution of gene and protein structure, transcriptional regulation and function across a phylogenetic lineage through comparative analyses.

Global Brassicaceae phylogeny based on filtering of 1,000-gene dataset

The mustard family (Brassicaceae) is a scientifically and economically important family, containing the model plant Arabidopsis thaliana and numerous crop species that feed billions worldwide. Despite its relevance, most phylogenetic trees of the family are incompletely sampled and often contain poorly supported branches. Here, we present the most complete Brassicaceae genus-level family phylogenies to date (Brassicaceae Tree of Life or BrassiToL) based on nuclear (1,081 genes, 319 of the 349 genera; 57 of the 58 tribes) and plastome (60 genes, 265 genera; all tribes) data. We found cytonuclear discordance between the two, which is likely a result of rampant hybridization among closely and more distantly related lineages. To evaluate the impact of such hybridization on the nuclear phylogeny reconstruction, we performed five different gene sampling routines, which increasingly removed putatively paralog genes. Our cleaned subset of 297 genes revealed high support for the tribes, whereas support for the main lineages (supertribes) was moderate. Calibration based on the 20 most clock-like nuclear genes suggests a late Eocene to late Oligocene origin of the family. Finally, our results strongly support a recently published new family classification, dividing the family into two subfamilies (one with five supertribes), together representing 58 tribes. This includes five recently described or re-established tribes, including Arabidopsideae, a monogeneric tribe accommodating Arabidopsis without any close relatives. With a worldwide community of thousands of researchers working on Brassicaceae and its diverse members, our new genus-level family phylogeny will be an indispensable tool for studies on biodiversity and plant biology.

Insights into the Evolution of Ohnologous Sequences and Their Epigenetic Marks Post-WGD in Malus Domestica

A Whole Genome Duplication (WGD) event occurred several Ma in a Rosaceae ancestor, giving rise to the Maloideae subfamily which includes today many pome fruits such as pear (Pyrus communis) and apple (Malus domestica). This complete and well-conserved genome duplication makes the apple an organism of choice to study the early evolutionary events occurring to ohnologous chromosome fragments. In this study, we investigated gene sequence evolution and expression, transposable elements (TE) density, and DNA methylation level. Overall, we identified 16,779 ohnologous gene pairs in the apple genome, confirming the relatively recent WGD. We identified several imbalances in QTL localization among duplicated chromosomal fragments and characterized various biases in genome fractionation, gene transcription, TE densities, and DNA methylation. Our results suggest a particular chromosome dominance in this autopolyploid species, a phenomenon that displays similarities with subgenome dominance that has only been described so far in allopolyploids.

Underestimated diversity in high elevations of a global biodiversity hotspot: two new endemic species of Aethionema (Brassicaceae) from the alpine zone of Iran

Although the mountains in South-West Asia are a global biodiversity hotspot, our understanding of their biodiversity, especially in the commonly remote alpine and subnival zones, is still limited. This is well exemplified here by Aethionema umbellatum (Brassicaceae), a species considered to have a wide yet disjoint distribution in the Zagros and Yazd-Kerman mountains of western and central Iran. Morphological and molecular phylogenetic data (based on plastid trnL-trnF and nuclear ITS sequences) show that A. umbellatum is restricted to a single mountain range in southwestern Iran (Dena Mts., southern Zagros), whereas populations from central Iran (Yazd-Kerman and central Zagros) and from western Iran (central Zagros) belong to species new to science, A. alpinum and A. zagricum, respectively. Both new species are phylogenetically and morphologically close to A. umbellatum, with which they share unilocular fruits and one-seeded locules. However, they are easily distinguishable by leaf shape, petal size, and fruit characters. This study confirms that the alpine flora of the Irano-Anatolian region is still poorly known. As the proportion of rare and local endemic species in alpine habitats is high, these habitats are of prime interest for conservation efforts.

The evolution of the hypotetraploid Catolobus pendulus genome - the poorly known sister species of Capsella

The establishment of Arabidopsis as the most important plant model has also brought other crucifer species into the spotlight of comparative research. While the genus Capsella has become a prominent crucifer model system, its closest relative has been overlooked. The unispecific genus Catolobus is native to temperate Eurasian woodlands, from eastern Europe to the Russian Far East. Here, we analyzed chromosome number, genome structure, intraspecific genetic variation, and habitat suitability of Catolobus pendulus throughout its range. Unexpectedly, all analyzed populations were hypotetraploid (2n = 30, ~330 Mb). Comparative cytogenomic analysis revealed that the Catolobus genome arose by a whole-genome duplication in a diploid genome resembling Ancestral Crucifer Karyotype (ACK, n = 8). In contrast to the much younger Capsella allotetraploid genomes, the presumably autotetraploid Catolobus genome (2n = 32) arose early after the Catolobus/Capsella divergence. Since its origin, the tetraploid Catolobus genome has undergone chromosomal rediploidization, including a reduction in chromosome number from 2n = 32 to 2n = 30. Diploidization occurred through end-to-end chromosome fusion and other chromosomal rearrangements affecting a total of six of 16 ancestral chromosomes. The hypotetraploid Catolobus cytotype expanded toward its present range, accompanied by some longitudinal genetic differentiation. The sister relationship between Catolobus and Capsella allows comparative studies of tetraploid genomes of contrasting ages and different degrees of genome diploidization.

A high-quality chromosome-level Eutrema salsugineum genome, an extremophile plant model

BACKGROUND

Eutrema salsugineum (2n = 14), a halophyte in the family Brassicaceae, is an attractive model to study abiotic stress tolerance in plants. Two versions of E. salsugineum genomes that previously reported were based on relatively short reads; thus, the repetitive regions were difficult to characterize.

RESULTS

We report the sequencing and assembly of the E. salsugineum (Shandong accession) genome using long-read sequencing and chromosome conformation capture data. We generated Oxford Nanopore long reads at high depth (> 60X) of genome coverage with additional short reads for error correction. The new assembly has a total size of 295.5 Mb with 52.8% repetitive sequences, and the karyotype of E. salsugineum is consistent with the ancestral translocation Proto-Calepineae Karyotype structure in both order and orientation. Compared with previous assemblies, this assembly has higher contiguity, especially in the centromere region. Based on this new assembly, we predicted 25,399 protein-coding genes and identified the positively selected genes associated with salt and drought stress responses.

CONCLUSION

The new genome assembly will provide a valuable resource for future genomic studies and facilitate comparative genomic analysis with other plants.

Nuclear phylogeny and insights into whole-genome duplications and reproductive development of Solanaceae plants

Solanaceae, the nightshade family, have ∼2700 species, including the important crops potato and tomato, ornamentals, and medicinal plants. Several sequenced Solanaceae genomes show evidence for whole-genome duplication (WGD), providing an excellent opportunity to investigate WGD and its impacts. Here, we generated 93 transcriptomes/genomes and combined them with 87 public datasets, for a total of 180 Solanaceae species representing all four subfamilies and 14 of 15 tribes. Nearly 1700 nuclear genes from these transcriptomic/genomic datasets were used to reconstruct a highly resolved Solanaceae phylogenetic tree with six major clades. The Solanaceae tree supports four previously recognized subfamilies (Goetzeioideae, Cestroideae, Nicotianoideae, and Solanoideae) and the designation of three other subfamilies (Schizanthoideae, Schwenckioideae, and Petunioideae), with the placement of several previously unassigned genera. We placed a Solanaceae-specific whole-genome triplication (WGT1) at ∼81 million years ago (mya), before the divergence of Schizanthoideae from other Solanaceae subfamilies at ∼73 mya. In addition, we detected two gene duplication bursts (GDBs) supporting proposed WGD events and four other GDBs. An investigation of the evolutionary histories of homologs of carpel and fruit developmental genes in 14 gene (sub)families revealed that 21 gene clades have retained gene duplicates. These were likely generated by the Solanaceae WGT1 and may have promoted fleshy fruit development. This study presents a well-resolved Solanaceae phylogeny and a new perspective on retained gene duplicates and carpel/fruit development, providing an improved understanding of Solanaceae evolution.

An updated classification of the Brassicaceae (Cruciferae)

Based on recent achievements in phylogenetic studies of the Brassicaceae, a novel infrafamilial classification is proposed that includes major improvements at the subfamilial and supertribal levels. Herein, the family is subdivided into two subfamilies, Aethionemoideae (subfam. nov.) and Brassicoideae. The Brassicoideae, with 57 of the 58 tribes of Brassicaceae, are further partitioned into five supertribes, including the previously recognized Brassicodae and the newly established Arabodae, Camelinodae, Heliophilodae, and Hesperodae. Additional tribus-level contributions include descriptions of the newly recognized Arabidopsideae, Asperuginoideae, Hemilophieae, Schrenkielleae, and resurrection of the Chamireae and Subularieae. Further detailed comments on 17 tribes in need of clarifications are provided.

Synteny Identifies Reliable Orthologs for Phylogenomics and Comparative Genomics of the Brassicaceae

Large genomic data sets are becoming the new normal in phylogenetic research, but the identification of true orthologous genes and the exclusion of problematic paralogs is still challenging when applying commonly used sequencing methods such as target enrichment. Here, we compared conventional ortholog detection using OrthoFinder with ortholog detection through genomic synteny in a data set of 11 representative diploid Brassicaceae whole-genome sequences spanning the entire phylogenetic space. Then, we evaluated the resulting gene sets regarding gene number, functional annotation, and gene and species tree resolution. Finally, we used the syntenic gene sets for comparative genomics and ancestral genome analysis. The use of synteny resulted in considerably more orthologs and also allowed us to reliably identify paralogs. Surprisingly, we did not detect notable differences between species trees reconstructed from syntenic orthologs when compared with other gene sets, including the Angiosperms353 set and a Brassicaceae-specific target enrichment gene set. However, the synteny data set comprised a multitude of gene functions, strongly suggesting that this method of marker selection for phylogenomics is suitable for studies that value downstream gene function analysis, gene interaction, and network studies. Finally, we present the first ancestral genome reconstruction for the Core Brassicaceae which predating the Brassicaceae lineage diversification ∼25 million years ago.

Transcriptome-based variations effectively untangling the intraspecific relationships and selection signals in Xinyang Maojian tea population

As one of the world's top three popular non-alcoholic beverages, tea is economically and culturally valuable. Xinyang Maojian, this elegant green tea, is one of the top ten famous tea in China and has gained prominence for thousands of years. However, the cultivation history of Xinyang Maojian tea population and selection signals of differentiation from the other major variety Camellia sinensis var. assamica (CSA) remain unclear. We newly generated 94 Camellia sinensis (C. sinensis) transcriptomes including 59 samples in the Xinyang area and 35 samples collected from 13 other major tea planting provinces in China. Comparing the very low resolution of phylogeny inferred from 1785 low-copy nuclear genes with 94 C. sinensis samples, we successfully resolved the phylogeny of C. sinensis samples by 99,115 high-quality SNPs from the coding region. The sources of tea planted in the Xinyang area were extensive and complex. Specifically, Shihe District and Gushi County were the two earliest tea planting areas in Xinyang, reflecting a long history of tea planting. Furthermore, we identified numerous selection sweeps during the differentiation of CSA and CSS and these positive selection genes are involved in many aspects such as regulation of secondary metabolites synthesis, amino acid metabolism, photosynthesis, etc. Numerous specific selective sweeps of modern cultivars were annotated with functions in various different aspects, indicating the CSS and CSA populations possibly underwent independent specific domestication processes. Our study indicated that transcriptome-based SNP-calling is an efficient and cost-effective method in untangling intraspecific phylogenetic relationships. This study provides a significant understanding of the cultivation history of the famous Chinese tea Xinyang Maojian and unravels the genetic basis of physiological and ecological differences between the two major tea subspecies.

Phylotranscriptomics Shed Light on Intrageneric Relationships and Historical Biogeography of Ceratozamia (Cycadales)

Ceratozamia Brongn. is one of the species-rich genera of Cycadales comprising 38 species that are mainly distributed in Mexico, with a few species reported from neighboring regions. Phylogenetic relationships within the genus need detailed investigation based on extensive datasets and reliable systematic approaches. Therefore, we used 30 of the known 38 species to reconstruct the phylogeny based on transcriptome data of 3954 single-copy nuclear genes (SCGs) via coalescent and concatenated approaches and three comparative datasets (nt/nt12/aa). Based on all these methods, Ceratozamia is divided into six phylogenetic subclades within three major clades. There were a few discrepancies regarding phylogenetic position of some species within these subclades. Using these phylogenetic trees, biogeographic history and morphological diversity of the genus are explored. Ceratozamia originated from ancestors in southern Mexico since the mid-Miocene. There is a distinct distribution pattern of species through the Trans-Mexican Volcanic Belt (TMVB), that act as a barrier for the species dispersal at TMVB and its southern and northern part. Limited dispersal events occurred during the late Miocene, and maximum diversification happened during the Pliocene epoch. Our study provides a new insight into phylogenetic relationships, the origin and dispersal routes, and morphological diversity of the genus Ceratozamia. We also explain how past climatic changes affected the diversification of this Mesoamerica-native genus.

Nested singletons in molecular trees: Utility of adding morphological and geographical data from digitized herbarium specimens to test taxon concepts at species level in the case of Casearia (Salicaceae)

Using the genus Casearia, we assessed the status of nested singletons: individual specimens corresponding to accepted species but in molecular trees appearing nested within clades of closely related species. Normally, such cases would be left undecided, while on the other hand, timely taxonomic decisions are required. We argue that morphological, chorological, and ecological data can be informative to illuminate patterns of speciation. Their use can provide a first step in testing taxon concepts at species level. We focused on five cases of nested singletons in trees of the genus Casearia. We employed PCA and cluster analysis to assess phenotypic differentiation. Using geocoordinates, we calculated niche space differentiation based on 19 bioclim variables, by means of PCA and niche equivalency and similarity tests and generated dot maps. We found that the singletons were morphologically distinctive in two of the five cases (Casearia selloana and C. manausensis), relatively distinctive in two other cases (C. zizyphoides and C. mariquitensis), and partially overlapping in the last case (C. grandiflora). For two cases (C. mariquitensis and C. selloana), ecological niche space was broadly overlapping, in two cases it was found broadly nested (C. grandiflora and C. zizyphoides), and in one case narrowly nested (C. manausensis), but in no case niche differentiation was observed. Niche overlap, similarity and equivalency showed corresponding patterns. Given these data, one would interpret C. selloana and C. manausensis as presumably well-distinguished taxa, their narrow distribution ranges suggesting recently emerging lineages. The other three cases are not clearcut. Morphological data would suggest particularly C. grandiflora conspecific with C. arborea, but differences in the distribution are intriguing. Our approach would reject the notion of potential synonymy based on nested phylogenetic placement for at least two of the five cases. The other case also shows no complete lack of differentiation which would support synonymy.

Diverse responses of halophyte and glycophyte Lepidium species to the salt-mediated amelioration of nickel toxicity and accumulation

Tolerance mechanisms employed by plants under environmental stresses can protect them against other co-occurring stresses. In this study, the effect of pre-exposure and simultaneous salt treatment on nickel (Ni) toxicity tolerance in one halophyte (L. sativum) and one glycophyte (L. latifolium) Lepidium species in hydroponics was investigated. In order to compare the species independent from their salt and Ni tolerance level, the glycophyte was subjected to lower salt and Ni concentrations and for a shorter period of time than the halophyte. Salt (NaCl) was applied at 50 and 100 mM concentrations and Ni was provided at an equal free Ni²⁺ activity by adding 100 and 200 µM Ni as single stresses, but 130 and 300 µM Ni for the treatment of its combination with salt in the glycophyte and halophyte, respectively. Temporal analyses of signaling molecules revealed that the halophyte is characteristically different from the glycophyte in that it exhibits a higher constitutive level of nitric oxide and hydrogen peroxide, a longer duration of response to Ni, and its augmentation by salt. In addition to higher biomass and less Ni accumulation in salt-treated plants, the concentrations of free thiol groups, leaf pigments, proline, free and cell wall-bound phenolics contents, and the activity of phenolic metabolizing enzymes were higher in L. latifolium under the combined salt and Ni treatments than under the single Ni stress. In contrast, the biomass and most biochemical parameters of Ni-stressed L. sativum plants were not enhanced by salt treatment but rather decreased. Our findings shed light on cross-tolerance mechanisms in halophytes and uncovered halophyte survival strategies under multiple stresses.

The genome sequence of Hirschfeldia incana, a new Brassicaceae model to improve photosynthetic light-use efficiency

Photosynthesis is a key process in sustaining plant and human life. Improving the photosynthetic capacity of agricultural crops is an attractive means to increase their yields. While the core mechanisms of photosynthesis are highly conserved in C₃ plants, these mechanisms are very flexible, allowing considerable diversity in photosynthetic properties. Among this diversity is the maintenance of high photosynthetic light-use efficiency at high irradiance as identified in a small number of exceptional C₃ species. Hirschfeldia incana, a member of the Brassicaceae family, is such an exceptional species, and because it is easy to grow, it is an excellent model for studying the genetic and physiological basis of this trait. Here, we present a reference genome of H. incana and confirm its high photosynthetic light-use efficiency. While H. incana has the highest photosynthetic rates found so far in the Brassicaceae, the light-saturated assimilation rates of closely related Brassica rapa and Brassica nigra are also high. The H. incana genome has extensively diversified from that of B. rapa and B. nigra through large chromosomal rearrangements, species-specific transposon activity, and differential retention of duplicated genes. Duplicated genes in H. incana, B. rapa, and B. nigra that are involved in photosynthesis and/or photoprotection show a positive correlation between copy number and gene expression, providing leads into the mechanisms underlying the high photosynthetic efficiency of these species. Our work demonstrates that the H. incana genome serves as a valuable resource for studying the evolution of high photosynthetic light-use efficiency and enhancing photosynthetic rates in crop species.

Comparative Analysis of the Chloroplast Genome of Cardamine hupingshanensis and Phylogenetic Study of Cardamine

Cardamine hupingshanensis (K. M. Liu, L. B. Chen, H. F. Bai and L. H. Liu) is a perennial herbal species endemic to China with narrow distribution. It is known as an important plant for investigating the metabolism of selenium in plants because of its ability to accumulate selenium. However, the phylogenetic position of this particular species in Cardamine remains unclear. In this study, we reported the chloroplast genome (cp genome) for the species C. hupingshanensis and analyzed its position within Cardamine. The cp genome of C. hupingshanensis is 155,226 bp in length and exhibits a typical quadripartite structure: one large single copy region (LSC, 84,287 bp), one small single copy region (17,943 bp) and a pair of inverted repeat regions (IRs, 26,498 bp). Guanine-Cytosine (GC) content makes up 36.3% of the total content. The cp genome contains 111 unique genes, including 78 protein-coding genes, 29 tRNA genes and 4 rRNA genes. A total of 115 simple sequences repeats (SSRs) and 49 long repeats were identified in the genome. Comparative analyses among 17 Cardamine species identified the five most variable regions (trnH-GUG-psbA, ndhK-ndhC, trnW-CCA-trnP-UGG, rps11-rpl36 and rpl32-trnL-UAG), which could be used as molecular markers for the classification and phylogenetic analyses of various Cardamine species. Phylogenetic analyses based on 79 protein coding genes revealed that the species C. hupingshanensis is more closely related to the species C. circaeoides. This relationship is supported by their shared morphological characteristics.

Phylogenomics as an effective approach to untangle cross-species hybridization event: A case study in the family Nymphaeaceae

Hybridization is common and considered as an important evolutionary force to increase intraspecific genetic diversity. Detecting hybridization events is crucial for understanding the evolutionary history of species and further improving molecular breeding. The studies on identifying hybridization events through the phylogenomic approach are still limited. We proposed the conception and method of identifying allopolyploidy events by phylogenomics. The reconciliation and summary of nuclear multi-labeled gene family trees were adopted to untangle hybridization events from next-generation data in our novel phylogenomic approach. Given horticulturalists’ relatively clear cultivated crossbreeding history, the water lily family is a suitable case for examining recent allopolyploidy events. Here, we reconstructed and confirmed the well-resolved nuclear phylogeny for the Nymphaeales family in the context of geological time as a framework for identifying hybridization signals. We successfully identified two possible allopolyploidy events with the parental lineages for the hybrids in the family Nymphaeaceae based on summarization from multi-labeled gene family trees of Nymphaeales. The lineages where species Nymphaea colorata and Nymphaea caerulea are located may be the progenitors of horticultural cultivated species Nymphaea ‘midnight’ and Nymphaea ‘Woods blue goddess’. The proposed hybridization hypothesis is also supported by horticultural breeding records. Our methodology can be widely applied to identify hybridization events and theoretically facilitate the genome breeding design of hybrid plants.

Genome-wide characterization of two Aubrieta taxa: Aubrieta canescens subsp. canescens and Au. macrostyla (Brassicaceae)

Aubrieta canescens complex is divided into two subspecies, Au. canescens subsp. canescens, Au. canescens subsp. cilicica and a distinct species, Au. macrostyla, based on molecular phylogeny. We generated a draft assembly of Au. canescens subsp. canescens and Au. macrostyla using paired-end shotgun sequencing. This is the first attempt at genome characterization for the genus. In the presented study, ~165 and ~157 Mbp of the genomes of Au. canescens subsp. canescens and Au. macrostyla were assembled, respectively, and a total of 32 425 and 31 372 gene models were predicted in the genomes of the target taxa, respectively. We corroborated the phylogenomic affinity of taxa with some core Brassicaceae species (Clades A and B) including Arabis alpina. The orthology-based tree suggested that Aubrieta species differentiated from A. alpina 1.3-2.0 mya (million years ago). The genome-wide syntenic comparison of two Aubrieta taxa revealed that Au. canescens subsp. canescens (46 %) and Au. macrostyla (45 %) have an almost identical syntenic gene pair ratio. These novel genome assemblies are the first steps towards the chromosome-level assembly of Au. canescens and understanding the genome diversity within the genus.

Genome diploidization associates with cladogenesis, trait disparity, and plastid gene evolution

Angiosperm genome evolution was marked by many clade-specific whole-genome duplication events. The Microlepidieae is one of the monophyletic clades in the mustard family (Brassicaceae) formed after an ancient allotetraploidization. Postpolyploid cladogenesis has resulted in the extant c. 17 genera and 60 species endemic to Australia and New Zealand (10 species). As postpolyploid genome diploidization is a trial-and-error process under natural selection, it may proceed with different intensity and be associated with speciation events. In Microlepidieae, different extents of homoeologous recombination between the two parental subgenomes generated clades marked by slow ("cold") versus fast ("hot") genome diploidization. To gain a deeper understanding of postpolyploid genome evolution in Microlepidieae, we analyzed phylogenetic relationships in this tribe using complete chloroplast sequences, entire 35S rDNA units, and abundant repetitive sequences. The four recovered intra-tribal clades mirror the varied diploidization of Microlepidieae genomes, suggesting that the intrinsic genomic features underlying the extent of diploidization are shared among genera and species within one clade. Nevertheless, even congeneric species may exert considerable morphological disparity (e.g. in fruit shape), whereas some species within different clades experience extensive morphological convergence despite the different pace of their genome diploidization. We showed that faster genome diploidization is positively associated with mean morphological disparity and evolution of chloroplast genes (plastid-nuclear genome coevolution). Higher speciation rates in perennials than in annual species were observed. Altogether, our results confirm the potential of Microlepidieae as a promising subject for the analysis of postpolyploid genome diploidization in Brassicaceae.

Analysis of flavonol regulator evolution in the Brassicaceae reveals MYB12, MYB111 and MYB21 duplications and MYB11 and MYB24 gene loss

Background

Flavonols are the largest subgroup of flavonoids, possessing multiple functions in plants including protection against ultraviolet radiation, antimicrobial activities, and flower pigmentation together with anthocyanins. They are of agronomical and economical importance because the major off-taste component in rapeseed protein isolates is a flavonol derivative, which limits rapeseed protein use for human consumption. Flavonol production in Arabidopsis thaliana is mainly regulated by the subgroup 7 (SG7) R2R3-MYB transcription factors MYB11, MYB12, and MYB111. Recently, the SG19 MYBs MYB21, MYB24, and MYB57 were shown to regulate flavonol accumulation in pollen and stamens. The members of each subgroup are closely related, showing gene redundancy and tissue-specific expression in A. thaliana. However, the evolution of these flavonol regulators inside the Brassicaceae, especially inside the Brassiceae, which include the rapeseed crop species, is not fully understood.

Results

We studied the SG7 and SG19 MYBs in 44 species, including 31 species of the Brassicaceae, by phylogenetic analyses followed by synteny and gene expression analyses. Thereby we identified a deep MYB12 and MYB111 duplication inside the Brassicaceae, which likely occurred before the divergence of Brassiceae and Thelypodieae. These duplications of SG7 members were followed by the loss of MYB11 after the divergence of Eruca vesicaria from the remaining Brassiceae species. Similarly, MYB21 experienced duplication before the emergence of the Brassiceae tribe, where the gene loss of MYB24 is also proposed to have happened. The members of each subgroup revealed frequent overlapping spatio-temporal expression patterns in the Brassiceae member B. napus, which are assumed to compensate for the loss of MYB11 and MYB24 in the analysed tissues.

Conclusions

We identified a duplication of MYB12, MYB111, and MYB21 inside the Brassicaceae and MYB11 and MYB24 gene loss inside the tribe Brassiceae. We propose that polyploidization events have shaped the evolution of the flavonol regulators in the Brassicaceae, especially in the Brassiceae.

The chloroplast genome of Farsetia hamiltonii Royle, phylogenetic analysis, and comparative study with other members of Clade C of Brassicaceae

BACKGROUND

Farsetia hamiltonii Royle is a medicinally important annual plant from the Cholistan desert that belongs to the tribe Anastaticeae and clade C of the Brassicaceae family. We provide the entire chloroplast sequence of F.hamiltonii, obtained using the Illumina HiSeq2500 and paired-end sequencing. We compared F. hamiltonii to nine other clade C species, including Farsetia occidentalis, Lobularia libyca, Notoceras bicorne, Parolinia ornata, Morettia canescens, Cochlearia borzaeana, Megacarpaea polyandra, Biscutella laevigata, and Iberis amara. We conducted phylogenetic research on the 22 Brassicaceae species, which included members from 17 tribes and six clades.

RESULTS

The chloroplast genome sequence of F.hamiltonii of 154,802 bp sizes with 36.30% GC content and have a typical structure comprised of a Large Single Copy (LSC) of 83,906 bp, a Small Single Copy (SSC) of 17,988 bp, and two copies of Inverted Repeats (IRs) of 26,454 bp. The genomes of F. hamiltonii and F. occidentalis show shared amino acid frequencies and codon use, RNA editing sites, simple sequence repeats, and oligonucleotide repeats. The maximum likelihood tree revealed Farsetia as a monophyletic genus, closely linked to Morettia, with a bootstrap score of 100. The rate of transversion substitutions (Tv) was higher than the rate of transition substitutions (Ts), resulting in Ts/Tv less than one in all comparisons with F. hamiltonii, indicating that the species are closely related. The rate of synonymous substitutions (Ks) was greater than non-synonymous substitutions (Ka) in all comparisons with F. hamiltonii, with a Ka/Ks ratio smaller than one, indicating that genes underwent purifying selection. Low nucleotide diversity values range from 0.00085 to 0.08516, and IR regions comprise comparable genes on junctions with minimal change, supporting the conserved status of the selected chloroplast genomes of the clade C of the Brassicaceae family. We identified ten polymorphic regions, including rps8-rpl14, rps15-ycf1, ndhG-ndhI, psbK-psbI, ccsA-ndhD, rpl36-rps8, petA-psbJ, ndhF-rpl32, psaJ-rpl3, and ycf1 that might be exploited to construct genuine and inexpensive to solve taxonomic discrepancy and understand phylogenetic relationship amongst Brassicaceae species.

CONCLUSION

The entire chloroplast sequencing of F. hamiltonii sheds light on the divergence of genic chloroplast sequences among members of the clade C. When other Farsetia species are sequenced in the future, the full F. hamiltonii chloroplast will be used as a source for comprehensive taxonomical investigations of the genus. The comparison of F. hamiltonii and other clade C species adds new information to the phylogenetic data and evolutionary processes of the clade. The results of this study will also provide further molecular uses of clade C chloroplasts for possible plant genetic modifications and will help recognise more Brassicaceae family species.

Idahoa and Subularia: Hidden polyploid origins of two enigmatic genera of crucifers

PREMISE

The monotypic Idahoa (I. scapigera) and the bispecific Subularia (S. aquatica and S. monticola) belong to Brassicaceae with unclear phylogenetic relationships and no tribal assignment. To fill this knowledge gap, we investigated these species and their closest relatives by combining cytogenomic and phylogenomic methods.

METHODS

We used whole plastome sequences in maximum likelihood and Bayesian inference analyses. We tested the phylogenetic informativeness of shared genomic repeats. We combined nuclear gene tree reconciliation and comparative chromosome painting (CCP) to examine the occurrence of past whole-genome duplications (WGDs).

RESULTS

The plastid data set corroborated the sister relationship between Idahoa and Subularia within the crucifer Lineage V but failed to resolve consistent topologies using both inference methods. The shared repetitive sequences provided conflicting pwhylogenetic signals. CCP analysis unexpectedly revealed that Idahoa (2n = 16) has a diploidized mesotetraploid genome, whereas two Subularia species (2n = 28 and 30) have diploidized mesoctoploid genomes. Several ancient allopolyploidy events have also been detected in closely related taxa (Chamira circaeoides, Cremolobeae, Eudemeae, and Notothlaspideae).

CONCLUSIONS

Our results suggest that the contentious phylogenetic placement of Idahoa and Subularia is best explained by two WGDs involving one or more shared parental genomes. The newly identified mesopolyploid genomes highlight the challenges of studying plant clades with complex polyploidy histories and provide a better framework for understanding genome evolution in the crucifer family.

Dynamic enhancer transcription associates with reprogramming of immune genes during pattern triggered immunity in Arabidopsis

Background

Enhancers are cis-regulatory elements present in eukaryote genomes, which constitute indispensable determinants of gene regulation by governing the spatiotemporal and quantitative expression dynamics of target genes, and are involved in multiple life processes, for instance during development and disease states. The importance of enhancer activity has additionally been highlighted for immune responses in animals and plants; however, the dynamics of enhancer activities and molecular functions in plant innate immunity are largely unknown. Here, we investigated the involvement of distal enhancers in early innate immunity in Arabidopsis thaliana.

Results

A group of putative distal enhancers producing low-abundance transcripts either unidirectionally or bidirectionally are identified. We show that enhancer transcripts are dynamically modulated in plant immunity triggered by microbe-associated molecular patterns and are strongly correlated with open chromatin, low levels of methylated DNA, and increases in RNA polymerase II targeting and acetylated histone marks. Dynamic enhancer transcription is correlated with target early immune gene expression patterns. Cis motifs that are bound by immune-related transcription factors, such as WRKYs and SARD1, are highly enriched within upregulated enhancers. Moreover, a subset of core pattern-induced enhancers are upregulated by multiple patterns from diverse pathogens. The expression dynamics of putative immunity-related enhancers and the importance of WRKY binding motifs for enhancer function were also validated.

Conclusions

Our study demonstrates the general occurrence of enhancer transcription in plants and provides novel information on the distal regulatory landscape during early plant innate immunity, providing new insights into immune gene regulation and ultimately improving the mechanistic understanding of the plant immune system.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01362-8.

Out of chaos: Phylogenomics of Asian Sonerileae

Sonerileae is a diverse Melastomataceae lineage comprising ca. 1000 species in 44 genera, with >70% of genera and species distributed in Asia. Asian Sonerileae are taxonomically intractable with obscure generic circumscriptions. The backbone phylogeny of this group remains poorly resolved, possibly due to complexity caused by rapid species radiation in early and middle Miocene, which hampers further systematic study. Here, we used genome resequencing data to reconstruct the phylogeny of Asian Sonerileae. Three parallel datasets, viz. single-copy ortholog (SCO), genomic SNPs, and whole plastome, were assembled from genome resequencing data of 205 species for this purpose. Based on these genome-scale data, we provided the first well resolved phylogeny of Asian Sonerileae, with 34 major clades identified and 74% of the interclade relationships consistently resolved by both SCO and genomic data. Meanwhile, widespread phylogenetic discordance was detected among SCO gene trees as well as species trees reconstructed using different tree estimation methods (concatenation/site-based coalescent method/summary method) or different datasets (SCO/genomic/plastome). We explored sources of discordance using multiple approaches and found that the observed discordance in Asian Sonerileae was mainly caused by a combination of biased distribution of missing data, random noise from uninformative genes, incomplete lineage sorting, and hybridization/introgression. Exploration of these sources can enable us to generate hypotheses for future testing, which is the first step towards understanding the evolution of Asian Sonerileae. We also detected high levels of homoplasy for some characters traditionally used in taxonomy, which explains current chaotic generic delimitations. The backbone phylogeny of Asian Sonerileae revealed in this study offers a solid basis for future taxonomic revision at the generic level.

Phylogenomics Resolves the Phylogeny of Theaceae by Using Low-Copy and Multi-Copy Nuclear Gene Makers and Uncovers a Fast Radiation Event Contributing to Tea Plants Diversity

Simple Summary

The Theaceae includes more than 300 species of great morphological diversity and has immense economic, cultural, and ornamental values. However, the evolutionary history of this family remains elusive. We integrated 91 genomes and transcriptome datasets of Theaceae and successfully resolved the phylogeny of Theaceae including relatives of cultivated tea plants from both extensive low-copy and multi-copy nuclear gene markers. Bayes-based molecular dating revealed that the ancestor of the tea family originated slightly earlier than the K-Pg boundary (Mass extinction events including the extinction of dinosaurs) with early diversification of three tribes associated with the Early Eocene Climatic Optimum. Further speciation analysis suggested a sole significant diversification shift rate in the common ancestor of Camellia associated with the Mid-Miocene Climatic Optimum. Collectively, polyploidy events, and key morphological innovation characters, such as pericarp with seed coat hardening, could possibly contribute to the Theaceae species diversity.

Abstract

Tea is one of the three most popular nonalcoholic beverages globally and has extremely high economic and cultural value. Currently, the classification, taxonomy, and evolutionary history of the tea family are largely elusive, including phylogeny, divergence, speciation, and diversity. For understanding the evolutionary history and dynamics of species diversity in Theaceae, a robust phylogenetic framework based on 1785 low-copy and 79,103 multi-copy nuclear genes from 91 tea plant genomes and transcriptome datasets had been reconstructed. Our results maximumly supported that the tribes Stewartieae and Gordonieae are successive sister groups to the tribe Theeae from both coalescent and super matrix ML tree analyses. Moreover, in the most evolved tribe, Theeae, the monophyletic genera Pyrenaria, Apterosperma, and Polyspora are the successive sister groups of Camellia. We also yield a well-resolved relationship of Camellia, which contains the vast majority of Theaceae species richness. Molecular dating suggests that Theaceae originated in the late L-Cretaceous, with subsequent early radiation under the Early Eocene Climatic Optimal (EECO) for the three tribes. A diversification rate shift was detected in the common ancestors of Camellia with subsequent acceleration in speciation rate under the climate optimum in the early Miocene. These results provide a phylogenetic framework and new insights into factors that likely have contributed to the survival of Theaceae, especially a successful radiation event of genus Camellia members to subtropic/tropic regions. These novel findings will facilitate the efficient conservation and utilization of germplasm resources for breeding cultivated tea and oil-tea. Collectively, these results provide a foundation for further morphological and functional evolutionary analyses across Theaceae.

Comparative transcriptomic analysis unveils the deep phylogeny and secondary metabolite evolution of 116 Camellia plants

Camellia plants include more than 200 species of great diversity and immense economic, ornamental, and cultural values. We sequenced the transcriptomes of 116 Camellia plants from almost all sections of the genus Camellia. We constructed a pan-transcriptome of Camellia plants with 89 394 gene families and then resolved the phylogeny of genus Camellia based on 405 high-quality low-copy core genes. Most of the inferred relationships are well supported by multiple nuclear gene trees and morphological traits. We provide strong evidence that Camellia plants shared a recent whole genome duplication event, followed by large expansions of transcription factor families associated with stress resistance and secondary metabolism. Secondary metabolites, particularly those associated with tea quality such as catechins and caffeine, were preferentially heavily accumulated in the Camellia plants from section Thea. We thoroughly examined the expression patterns of hundreds of genes associated with tea quality, and found that some of them exhibited significantly high expression and correlations with secondary metabolite accumulations in Thea species. We also released a web-accessible database for efficient retrieval of Camellia transcriptomes. The reported transcriptome sequences and obtained novel findings will facilitate the efficient conservation and utilization of Camellia germplasm towards a breeding program for cultivated tea, camellia, and oil-tea plants.

What can cold-induced transcriptomes of Arctic Brassicaceae tell us about the evolution of cold tolerance?

Little is known about the evolution of cold tolerance in polar plant species and how they differ from temperate relatives. To gain insight into their biology and the evolution of cold tolerance, we compared the molecular basis of cold response in three Arctic Brassicaceae species. We conducted a comparative time series experiment to examine transcriptional responses to low temperature. RNA was sampled at 22°C, and after 3, 6, and 24 at 2°C. We then identified sets of genes that were differentially expressed in response to cold and compared them between species, as well as to published data from the temperate Arabidopsis thaliana. Most differentially expressed genes were species‐specific, but a significant portion of the cold response was also shared among species. Among thousands of differentially expressed genes, ~200 were shared among the three Arctic species and A. thaliana, while ~100 were exclusively shared among the three Arctic species. Our results show that cold response differs markedly between Arctic Brassicaceae species, but probably builds on a conserved basis found across the family. They also confirm that highly polygenic traits such as cold tolerance may show little repeatability in their patterns of adaptation.

Convergent evolution of polyploid genomes from across the eukaryotic tree of life

By modeling the homoeologous gene losses that occurred in 50 genomes deriving from ten distinct polyploidy events, we show that the evolutionary forces acting on polyploids are remarkably similar, regardless of whether they occur in flowering plants, ciliates, fishes, or yeasts. We show that many of the events show a relative rate of duplicate gene loss before the first postpolyploidy speciation that is significantly higher than in later phases of their evolution. The relatively weak selective constraint experienced by the single-copy genes these losses produced leads us to suggest that most of the purely selectively neutral duplicate gene losses occur in the immediate postpolyploid period. Nearly all of the events show strong evidence of biases in the duplicate losses, consistent with them being allopolyploidies, with 2 distinct progenitors contributing to the modern species. We also find ongoing and extensive reciprocal gene losses (alternative losses of duplicated ancestral genes) between these genomes. With the exception of a handful of closely related taxa, all of these polyploid organisms are separated from each other by tens to thousands of reciprocal gene losses. As a result, it is very unlikely that viable diploid hybrid species could form between these taxa, since matings between such hybrids would tend to produce offspring lacking essential genes. It is, therefore, possible that the relatively high frequency of recurrent polyploidies in some lineages may be due to the ability of new polyploidies to bypass reciprocal gene loss barriers.

Phylogenomic Analyses of Alismatales Shed Light into Adaptations to Aquatic Environments

Land plants first evolved from freshwater algae, and flowering plants returned to water as early as the Cretaceous and multiple times subsequently. Alismatales is the largest clade of aquatic angiosperms including all marine angiosperms, as well as terrestrial plants. We used Alismatales to explore plant adaptations to aquatic environments by analyzing a data set that included 95 samples (89 Alismatales species) covering four genomes and 91 transcriptomes (59 generated in this study). To provide a basis for investigating adaptations, we assessed phylogenetic conflict and whole-genome duplication (WGD) events in Alismatales. We recovered a relationship for the three main clades in Alismatales as (Tofieldiaceae, Araceae) + core Alismatids. We also found phylogenetic conflict among the three main clades that was best explained by incomplete lineage sorting and introgression. Overall, we identified 18 putative WGD events across Alismatales. One of them occurred at the most recent common ancestor of core Alismatids, and three occurred at seagrass lineages. We also found that lineage and life-form were both important for different evolutionary patterns for the genes related to freshwater and marine adaptation. For example, several light- or ethylene-related genes were lost in the seagrass Zosteraceae, but are present in other seagrasses and freshwater species. Stomata-related genes were lost in both submersed freshwater species and seagrasses. Nicotianamine synthase genes, which are important in iron intake, expanded in both submersed freshwater species and seagrasses. Our results advance the understanding of the adaptation to aquatic environments and WGDs using phylogenomics.

A well-supported nuclear phylogeny of Poaceae and implications for the evolution of C4 photosynthesis

Poaceae (the grasses) includes rice, maize, wheat, and other crops, and is the most economically important angiosperm family. Poaceae is also one of the largest plant families, consisting of over 11 000 species with a global distribution that contributes to diverse ecosystems. Poaceae species are classified into 12 subfamilies, with generally strong phylogenetic support for their monophyly. However, many relationships within subfamilies, among tribes and/or subtribes, remain uncertain. To better resolve the Poaceae phylogeny, we generated 342 transcriptomic and seven genomic datasets; these were combined with other genomic and transcriptomic datasets to provide sequences for 357 Poaceae species in 231 genera, representing 45 tribes and all 12 subfamilies. Over 1200 low-copy nuclear genes were retrieved from these datasets, with several subsets obtained using additional criteria, and used for coalescent analyses to reconstruct a Poaceae phylogeny. Our results strongly support the monophyly of 11 subfamilies; however, the subfamily Puelioideae was separated into two non-sister clades, one for each of the two previously defined tribes, supporting a hypothesis that places each tribe in a separate subfamily. Molecular clock analyses estimated the crown age of Poaceae to be ∼101 million years old. Ancestral character reconstruction of C₃/C₄ photosynthesis supports the hypothesis of multiple independent origins of C₄ photosynthesis. These origins are further supported by phylogenetic analysis of the ppc gene family that encodes the phosphoenolpyruvate carboxylase, which suggests that members of three paralogous subclades (ppc-aL1a, ppc-aL1b, and ppc-B2) were recruited as functional C₄ppc genes. This study provides valuable resources and a robust phylogenetic framework for evolutionary analyses of the grass family.

Phylotranscriptomics of Theaceae: generic-level relationships, reticulation and whole-genome duplication

BACKGROUND AND AIMS

Theaceae, with three tribes, nine genera and more than 200 species, are of great economic and ecological importance. Recent phylogenetic analyses based on plastomic data resolved the relationships among the three tribes and the intergeneric relationships within two of those tribes. However, generic-level relationships within the largest tribe, Theeae, were not fully resolved. The role of putative whole-genome duplication (WGD) events in the family and possible hybridization events among genera within Theeae also remain to be tested further.

METHODS

Transcriptomes or low-depth whole-genome sequencing of 57 species of Theaceae, as well as additional plastome sequence data, were generated. Using a dataset of low-copy nuclear genes, we reconstructed phylogenetic relationships using concatenated, species tree and phylogenetic network approaches. We further conducted molecular dating analyses and inferred possible WGD events by examining the distribution of the number of synonymous substitutions per synonymous site (Ks) for paralogues in each species. For plastid protein-coding sequences , phylogenies were reconstructed for comparison with the results obtained from analysis of the nuclear dataset.

RESULTS

Based on the 610 low-copy nuclear genes (858 606 bp in length) investigated, Stewartieae was resolved as sister to the other two tribes. Within Theeae, the Apterosperma-Laplacea clade grouped with Pyrenaria, leaving Camellia and Polyspora as sister. The estimated ages within Theaceae were largely consistent with previous studies based mainly on plastome data. Two reticulation events within Camellia and one between the common ancestor of Gordonia and Schima were found. All members of the tea family shared two WGD events, an older At-γ and a recent Ad-β; both events were also shared with the outgroups (Diapensiaceae, Pentaphylacaceae, Styracaceae and Symplocaceae).

CONCLUSIONS

Our analyses using low-copy nuclear genes improved understanding of phylogenetic relationships at the tribal and generic levels previously proposed based on plastome data, but the phylogenetic position of the Apterosperma-Laplacea clade needs more attention. There is no evidence for extensive intergeneric hybridization within Theeae or for a Theaceae-specific WGD event. Land bridges (e.g. the Bering land bridge) during the Late Oligocene may have permitted the intercontinental plant movements that facilitated the putative ancient introgression between the common ancestor of Gordonia and Schima.

Phylotranscriptomics Resolves the Phylogeny of Pooideae and Uncovers Factors for Their Adaptive Evolution

Adaptation to cool climates has occurred several times in different angiosperm groups. Among them, Pooideae, the largest grass subfamily with ∼3,900 species including wheat and barley, have successfully occupied many temperate regions and play a prominent role in temperate ecosystems. To investigate possible factors contributing to Pooideae adaptive evolution to cooling climates, we performed phylogenetic reconstruction using five gene sets (with 1,234 nuclear genes and their subsets) from 157 transcriptomes/genomes representing all 15 tribes and 24 of 26 subtribes. Our phylogeny supports the monophyly of all tribes (except Diarrheneae) and all subtribes with at least two species, with strongly supported resolution of their relationships. Molecular dating suggests that Pooideae originated in the late Cretaceous, with subsequent divergences under cooling conditions first among many tribes from the early middle to late Eocene and again among genera in the middle Miocene and later periods. We identified a cluster of gene duplications (CGD5) shared by the core Pooideae (with 80% Pooideae species) near the Eocene–Oligocene transition, coinciding with the transition from closed to open habitat and an upshift of diversification rate. Molecular evolutionary analyses homologs of CBF for cold resistance uncovered tandem duplications during the core Pooideae history, dramatically increasing their copy number and possibly promoting adaptation to cold habitats. Moreover, duplication of AP1/FUL-like genes before the Pooideae origin might have facilitated the regulation of the vernalization pathway under cold environments. These and other results provide new insights into factors that likely have contributed to the successful adaptation of Pooideae members to temperate regions.

Phenotypic plasticity guides Moricandia arvensis divergence and convergence across the Brassicaceae floral morphospace

Many flowers exhibit phenotypic plasticity. By inducing the production of several phenotypes, plasticity may favour the rapid exploration of different regions of the floral morphospace. We investigated how plasticity drives Moricandia arvensis, a species displaying within-individual floral polyphenism, across the floral morphospace of the entire Brassicaceae family. We compiled the multidimensional floral phenotype, the phylogenetic relationships, and the pollination niche of over 3000 species to construct a family-wide floral morphospace. We assessed the disparity between the two M. arvensis floral morphs (as the distance between the phenotypic spaces occupied by each morph) and compared it with the family-wide disparity. We measured floral divergence by comparing disparity with the most common ancestor, and estimated the convergence of each floral morph with other species belonging to the same pollination niches. Moricandia arvensis exhibits a plasticity-mediated floral disparity greater than that found between species, genera and tribes. The novel phenotype of M. arvensis moves outside the region occupied by its ancestors and relatives, crosses into a new region where it encounters a different pollination niche, and converges with distant Brassicaceae lineages. Our study suggests that phenotypic plasticity favours floral divergence and rapid appearance of convergent flowers, a process which facilitates the evolution of generalist pollination systems.

A chromosome-level genome assembly of an alpine plant Crucihimalaya lasiocarpa provides insights into high-altitude adaptation

It remains largely unknown how plants adapt to high-altitude habitats. Crucihimalaya (Brassicaceae) is an alpine genus occurring in the Qinghai-Tibet Plateau characterized by cold temperatures and strong ultraviolet radiation. Here, we generated a chromosome-level genome for C. lasiocarpa with a total size of 255.8 Mb and a scaffold N50 size of 31.9 Mb. We first examined the karyotype origin of this species and found that the karyotype of five chromosomes resembled the ancestral karyotype of the Brassicaceae family, while the other three showed strong chromosomal structural variations. In combination with the rough genome sequence of another congener (C. himalaica), we found that the significantly expanded gene families and positively selected genes involved in alpine adaptation have occurred since the origin of this genus. Our new findings provide valuable information for the chromosomal karyotype evolution of Brassicaceae and investigations of high-altitude environment adaptation of the genus.

Genome-wide investigation of AP2/ERF gene family in the desert legume Eremosparton songoricum: Identification, classification, evolution, and expression profiling under drought stress

Eremosparton songoricum (Litv.) Vass. is a rare leafless legume shrub endemic to central Asia which grows on bare sand. It shows extreme drought tolerance and is being developed as a model organism for investigating morphological, physiological, and molecular adaptations to harsh desert environments. APETALA2/Ethylene Responsive Factor (AP2/ERF) is a large plant transcription factor family that plays important roles in plant responses to various biotic and abiotic stresses and has been extensively studied in several plants. However, our knowledge on the AP2/ERF family in legume species is limited, and no respective study was conducted so far on the desert shrubby legume E. songoricum. Here, 153 AP2/ERF genes were identified based on the E. songoricum genome data. EsAP2/ERFs covered AP2 (24 genes), DREB (59 genes), ERF (68 genes), and Soloist (2 genes) subfamilies, and lacked canonical RAV subfamily genes based on the widely used classification method. The DREB and ERF subfamilies were further divided into A1-A6 and B1-B6 groups, respectively. Protein motifs and exon-intron structures of EsAP2/ERFs were also examined, which matched the subfamily/group classification. Cis-acting element analysis suggested that EsAP2/ERF genes shared many stress- and hormone-related cis-regulatory elements. Moreover, the gene numbers and the ratio of each subfamily and the intron-exon structures were systematically compared with other model plants ranging from algae to angiosperms, including ten legumes. Our results supported the view that AP2 and ERF evolved early and already existed in algae, whereas RAV and DREB began to appear in moss species. Almost all plant AP2 and Soloist genes contained introns, whereas most DREB and ERF genes did not. The majority of EsAP2/ERFs were induced by drought stress based on RNA-seq data, EsDREBs were highly induced and had the largest number of differentially expressed genes in response to drought. Eight out of twelve representative EsAP2/ERFs were significantly up-regulated as assessed by RT-qPCR. This study provides detailed insights into the classification, gene structure, motifs, chromosome distribution, and gene expression of AP2/ERF genes in E. songoricum and lays a foundation for better understanding of drought stress tolerance mechanisms in legume plants. Moreover, candidate genes for drought-resistant plant breeding are proposed.

PlantTribes2: Tools for comparative gene family analysis in plant genomics

Plant genome-scale resources are being generated at an increasing rate as sequencing technologies continue to improve and raw data costs continue to fall; however, the cost of downstream analyses remains large. This has resulted in a considerable range of genome assembly and annotation qualities across plant genomes due to their varying sizes, complexity, and the technology used for the assembly and annotation. To effectively work across genomes, researchers increasingly rely on comparative genomic approaches that integrate across plant community resources and data types. Such efforts have aided the genome annotation process and yielded novel insights into the evolutionary history of genomes and gene families, including complex non-model organisms. The essential tools to achieve these insights rely on gene family analysis at a genome-scale, but they are not well integrated for rapid analysis of new data, and the learning curve can be steep. Here we present PlantTribes2, a scalable, easily accessible, highly customizable, and broadly applicable gene family analysis framework with multiple entry points including user provided data. It uses objective classifications of annotated protein sequences from existing, high-quality plant genomes for comparative and evolutionary studies. PlantTribes2 can improve transcript models and then sort them, either genome-scale annotations or individual gene coding sequences, into pre-computed orthologous gene family clusters with rich functional annotation information. Then, for gene families of interest, PlantTribes2 performs downstream analyses and customizable visualizations including, (1) multiple sequence alignment, (2) gene family phylogeny, (3) estimation of synonymous and non-synonymous substitution rates among homologous sequences, and (4) inference of large-scale duplication events. We give examples of PlantTribes2 applications in functional genomic studies of economically important plant families, namely transcriptomics in the weedy Orobanchaceae and a core orthogroup analysis (CROG) in Rosaceae. PlantTribes2 is freely available for use within the main public Galaxy instance and can be downloaded from GitHub or Bioconda. Importantly, PlantTribes2 can be readily adapted for use with genomic and transcriptomic data from any kind of organism.