Nuclear phylotranscriptomics and phylogenomics support numerous polyploidization events and hypotheses for the evolution of rhizobial nitrogen-fixing symbiosis in Fabaceae

Phylogenomics reveals a new generic delimitation of Asian Millettia, with reinstatements of Pongamia and Otosema (Fabaceae: Millettieae)

The generic relationships within the core Millettieae have not been well resolved to date. Millettia is considered one of the most problematic genera to classify within the core Millettieae, with approximately 150 species found in Asia and Africa. Recent molecular evidence has indicated that Millettia is highly polyphyletic. In this study, we utilized plastomes and single-copy nuclear genes from genome skimming sequencing to reconstruct the generic relationships and estimate the divergence time for the core Millettieae, focusing on the Asian species of Millettia. Our results revealed a broader circumscription of the core Millettieae with the inclusion of the Phaseoleae subtribe Ophrestiinae, consisting of 7 clades and 14 subclades within two main groups (canavanine and non-canavanine). The Asian species of Millettia were grouped into three distinct, well-supported subclades, leading us to propose a much narrower generic concept of Millettia, along with the reinstatements of the genera Pongamia and Otosema. Millettia s.str. was restricted to include only seven species. Pongamia was recognized as a medium-sized genus that includes Fordia and Ibatiria, with approximately 56 species. Otosema, usually treated as a subgenus or section of Millettia, was resurrected as a distinct genus with three species. Our findings also indicated that the sampled African Millettia species belong to three subclades distinct from the Asian Millettia subclades, warranting further investigation in future studies. The dating result showed that the early rapid diversification of the core Millettieae during the Mid-Miocene Climatic Optimum involved several major problematic genera, including Derris s.lato, Lonchocarpus s.lato, and Millettia s.lato, which may explain why these plant groups are difficult to classify. These results offer new insights into the phylogeny and taxonomy of the core Millettieae.

Phylogenomic analyses unravel the tangled evolutionary history of Genisteae (Fabaceae)

Genisteae, a tribe in the subfamily Papilionoideae (Fabaceae), is characterized by the production of quinolizidine alkaloids that confer pest resistance in most of its members. Many relationships at the generic level remain unresolved due largely to a lack of modern attempts to reconstruct the phylogeny. Previous studies with limited taxon sampling and only a few molecular loci indicated the presence of three clades within the tribe: the Lupinus clade, the Cytisus-Genista complex and the Argyrolobium group. There are also two historical genera, Teline and Chamaecytisus, that have been reclassified over the years with some controversy. Species from Teline are currently classified in Genista, and Chamaecytisus species are placed inside of Cytisus. Sellocharis is another genus with vague placement inside of Genisteae near Anarthrophyllum, based mostly on morphology and cytology. Representative taxa from 24 of the 25 genera of Genisteae, along with species of historical genera Teline and Chamaecytisus, were sampled and utilized in a phylogenomic investigation using both plastid and nuclear data to resolve relationships at the generic level. Whole genomic DNA was sequenced and complete plastomes were assembled and annotated. Low-copy nuclear genes were retrieved from the genomic DNA sequences using a mapping-assembly-scaffold approach. Phylogenetic analyses using maximum likelihood, Bayesian and coalescence methods resulted in fully resolved and strongly supported trees for both nuclear and plastid data that show four major clades inside of Genisteae: Cytisus-Genista complex, Lupinus clade, Argyrolobium group and the novel Anarthrophyllum group. The resulting phylogenetic trees also supported the transfer of the Argyrolobium group from Crotalarieae to Genisteae, and the reclassification of Teline inside of Genista, both of which were previously suggested in literature. The phylogenetic trees also determined a placement for Sellocharis in the new Anarthrophyllum group. Although both nuclear and plastid trees were congruent with respect to the monophyly and relationships among the four major clades, incongruence was detected within some of the major clades and the potential causes are discussed.

Genomic insights into drought adaptation of the forage shrub Caragana korshinskii (Fabaceae) widely planted in drylands

The Korshinsk peashrub (Caragana korshinskii), known for its exceptional drought tolerance, is widely cultivated in arid and semi-arid regions for vegetation restoration and as a vital forage plant. To elucidate the genomic basis of its drought tolerance, we generated a chromosomal-scale genome sequence of C. korshinskii. Our synteny analysis disputes the previously hypothesized genus-specific whole-genome duplication event, as suggested by earlier transcriptome study of this species and its congeners. We identified that tandem duplications were critical for the expansion of gene families, such as early light-induced protein, heat shock protein 100, and Dehydrin, which are involved in cellular protection processes. These expansions are likely pivotal to the superior drought tolerance observed in C. korshinskii, as evidenced by the elevated gene expression of these genes under drought conditions. Furthermore, overexpression studies of seven tandemly duplicated DHN genes revealed a substantial enhancement in drought survival rates of seedlings, likely attributable to increased gene dosage effects. Conversely, gene silencing via virus-induced gene silencing demonstrated opposing effects. Additionally, we have established the CakorDB, a genomic resource database for C. korshinskii (https://bis.zju.edu.cn/cakordb/), accessible freely to the scientific community. Collectively, our study not only provides a valuable genomic resource for the Korshinsk peashrub but also highlights the genetic adaptations that enable C. korshinskii to thrive in desert environments, positioning its stress-responsive genes as a valuable genetic reservoir for breeding drought-resistant crops.

Convergent evidence for the temperature-dependent emergence of silicification in terrestrial plants

Research on silicon (Si) biogeochemistry and its beneficial effects for plants has received significant attention over several decades, but the reasons for the emergence of high-Si plants remain unclear. Here, we combine experimentation, field studies and analysis of existing databases to test the role of temperature on the expression and emergence of silicification in terrestrial plants. We first show that Si is beneficial for rice under high temperature (40 °C), but harmful under low temperature (0 °C), whilst a 2 °C increase results in a 37% increase in leaf Si concentrations. We then find that, globally, the average distribution temperature of high-Si plant clades is 1.2 °C higher than that of low-Si clades. Across China, leaf Si concentrations increase with temperature in high-Si plants (wheat and rice), but not in low-Si plants (weeping willow and winter jasmine). From an evolutionary perspective, 77% of high-Si families (>10 mg Si g-1 DW) originate during warming episodes, while 86% of low-Si families (<1 mg Si g-1 DW) originate during cooling episodes. On average, Earth's temperature during the emergence of high-Si families is 3 °C higher than that of low-Si families. Taken together, our evidence suggests that plant Si variation is closely related to global and long-term climate change.

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 Complete Chloroplast Genome of Erythrina variegata L. (Papilionoideae, Fabaceae)

Erythrina variegata L. 1754, a thorny deciduous tree of Fabaceae, contains various chemical compounds such as alkaloids, flavonoids, and triterpenoids and exhibits anti-depressant, anti-inflammatory, and antidiabetic activities. However, genomic data of E. variegata are limited. In this study, the complete chloroplast genome of E. variegata was sequenced and characterized using Illumina sequencing platform. The chloroplast genome of E. variegata was 152,351 bp in length and consisted of a large single copy (82,907 bp), a small single copy (26,309 bp), and two inverted repeat regions (16,826 bp). There were 79 protein-coding genes, 30 transfer RNA genes, and four ribosomal RNA genes. Comparative analysis revealed high conservation of chloroplast genomes among Erythrina species regarding genome size, structure, and gene content. The phylogenetic study also indicated a close relationship between E. variagata and E. sanwicensis. This study provides initial plastome data for further genomic studies examining E. variegata and related species in Fabaceae.

Ecological analysis of plant community structure and soil effects in subtropical forest ecosystem

BACKGROUND

Subtropical forest plant diversity, characterized by a wide range of species adapted to seasonal variations, is vital for sustaining ecological balance, supporting diverse wildlife, and providing critical ecosystem services such as carbon sequestration and soil stabilization. The Changa Manga Forest, an ecologically rich area with varied vegetation, was analyzed to understand the intricate relationship between plant diversity and environmental factors. This study investigates the diversity patterns, vegetation structure, and environmental influences on forest biodiversity.

METHODS

A comprehensive survey was conducted across 127 stands within the Changa Manga Forest to document plant species and classify vegetation communities. Soil samples were collected and analyzed for key physicochemical parameters, while multivariate statistical methods, including hierarchical clustering and ordination, were applied to examine the relationships between vegetation structure and environmental factors. Diversity indices and beta diversity components were calculated to assess variations across plant communities.

RESULTS

The species were classified into six distinct vegetation communities: Neltuma-Ziziphus-Malvestrum (NZM), Broussonetia-Lantana-Morus (BLM), Dalbergia-Lantana-Solanum (DLS), Morus-Abutilon-Ricinus (MAR), Eucalyptus-Vachellia-Sorghum (EVS), and Bombax-Leucaena-Croton (BLC). Analyses using hierarchical clustering and ordination methods revealed significant differences in species composition among these communities, with NZM and DLS exhibiting the highest dissimilarity. Canonical Correspondence Analysis (CCA) indicated that environmental factors such as soil pH, available phosphorus (AP), and organic matter percentage (OM%) are crucial in shaping plant distribution, though the total explained variation remained relatively low. Diversity indices varied significantly among communities, with the NZM community showing the highest Shannon and Simpson diversity, while EVS exhibited the lowest. The beta diversity analysis revealed a high species turnover between certain communities, indicating complex ecological interactions. Our results indicate significant variability in plant community composition and diversity patterns, influenced by edaphic factors and environmental gradients. We anticipate that future environmental changes, such as shifts in soil properties, precipitation patterns, and increased human activity, may exacerbate declines in local plant species richness and disrupt community structures. To preserve the invaluable biodiversity of the study area for future generations, it is essential to implement timely and effective conservation and management strategies.

Protein import into bacterial endosymbionts and evolving organelles

Bacterial endosymbionts are common throughout the eukaryotic tree of life and provide a range of essential functions. The intricate integration of bacterial endosymbionts into a host led to the formation of the energy-converting organelles, mitochondria and plastids, that have shaped eukaryotic evolution. Protein import from the host has been regarded as one of the distinguishing features of organelles as compared to endosymbionts. In recent years, research has delved deeper into a diverse range of endosymbioses and discovered evidence for 'exceptional' instances of protein import outside of the canonical organelles. Here we review the current evidence for protein import into bacterial endosymbionts. We cover both 'recently evolved' organelles, where there is evidence for hundreds of imported proteins, and endosymbiotic systems where currently only single protein import candidates are described. We discuss the challenges of establishing protein import machineries and the diversity of mechanisms that have independently evolved to solve them. Understanding these systems and the different independent mechanisms, they have evolved is critical to elucidate how cellular integration arises and deepens at the endosymbiont to organelle interface. We finish by suggesting approaches that could be used in the future to address the open questions. Overall, we believe that the evidence now suggests that protein import into bacterial endosymbionts is more common than generally realized, and thus that there is an increasing number of partnerships that blur the distinction between endosymbiont and organelle.

Paralogous Gene Recruitment in Multiple Families Constitutes Genetic Architecture and Robustness of Pod Dehiscence in Legumes

Pod dehiscence facilitates seed dispersal in wild legumes while indehiscence is a key domestication trait in cultivated ones. However, the evolutionary genetic mechanisms underlying its diversity are largely unclear. In this study, we compared transcriptomes of two warm-season (Glycine spp. and Phaseolus spp.) and two cool-season (Pisum spp. and Medicago ruthenica) legumes in analysis of dehiscent and indehiscent pod genotypes. Differentially expressed genes in AP2/ERF-like transcription factors and seven structural gene families, including lactoperoxidase, laccase, and cellulose synthase-interactive proteins, which are involved in secondary cell wall component accumulation, were identified to exert key roles in pod dehiscence variation. In accordance with this, higher lignin and cellulose contents were observed in pod secondary cell wall of dehiscent accessions of soybean and pea; however, the variation patterns of lignin polymers in soybean (accumulation) and pea (proportion) differed between dehiscent and indehiscent pods. Moreover, genome-wide comparative analysis revealed that orthogroups represented <1% of all identified differentially expressed genes could be traced among the four genera of legumes, while recruiting paralogous members may constitute the genetic robustness of legume pod dehiscence. This study compared the genetic mechanism among several legumes in pod dehiscence formation and revealed a compensating role of paralogous redundancy of involved gene families in seed dispersal, which can guide crop breeding.

Phylogenomic analyses of the pantropical Platycerium Desv. (Platycerioideae) reveal their complex evolution and historical biogeography

Platycerium is a genus of pantropical epiphytic ferns consisting of ca. 18 species and are highly sought after by horticultural enthusiasts. Although the monophyly of this genus has been well supported in previous molecular studies, as an intercontinentally disjunct genus, the origin and distribution pattern of Platycerium were elusive and controversial. This is mainly due to limited taxon sampling, a plastid representing only a single coalescent history, the lack of fossil evidence, and so on. Here, by utilizing genome-skimming sequencing, transcriptome sequencing, and flow cytometry, we integrated chloroplast genomes, data of single-copy nuclear genes, ploidy levels, morphology, and geographic distribution to understand the species phylogeny and the evolutionary and biogeographic history of Platycerium. Our major results include: (1) based on both plastid and nuclear datasets, Platycerium is consistently resolved into three fully supported clades: the Afro-American (AA) clade, the Javan-Australian (JA) clade, and the Malayan-Asian (MA) clade. The AA clade and MA clade are further divided into three and two subclades, respectively; (2) a large amount of gene tree conflict, as well as cytonuclear discordance, was found and can be explained by hybridization and incomplete lineage sorting, and most of the hybridization hypotheses represented ancient hybridization events; (3) through molecular dating, the crown age of Platycerium is determined to be at approximately 32.79 Ma based on the plastid dataset or 29.08 Ma based on the nuclear dataset in the Middle Oligocene; (4) ancestral area reconstruction analysis from different datasets showed that Platycerium most likely originated from Indochina; (5) current distribution patterns are resultant from long-distance dispersals, ancient orogeny, and an ancient climate event; and (6) species diversification was driven by polyploidization, dispersal, and hybridization. This study presented here will help understand the evolution of tropical plant flora and provide a reference for the cultivation and breeding of staghorn ferns.

Patterns and Mechanisms of Legume Responses to Nitrogen Enrichment: A Global Meta-Analysis

Nitrogen (N), while the most abundant element in the atmosphere, is an essential soil nutrient that limits plant growth. Leguminous plants naturally possess the ability to fix atmospheric nitrogen through symbiotic relationships with rhizobia in their root nodules. However, the widespread use of synthetic N fertilizers in modern agriculture has led to N enrichment in soils, causing complex and profound effects on legumes. Amid ongoing debates about how leguminous plants respond to N enrichment, the present study compiles 2174 data points from 162 peer-reviewed articles to analyze the impacts and underlying mechanisms of N enrichment on legumes. The findings reveal that N enrichment significantly increases total legume biomass by 30.9% and N content in plant tissues by 13.2% globally. However, N enrichment also leads to notable reductions, including a 5.8% decrease in root-to-shoot ratio, a 21.2% decline in nodule number, a 29.3% reduction in nodule weight, and a 27.1% decrease in the percentage of plant N derived from N2 fixation (%Ndfa). Legume growth traits and N2-fixing capability in response to N enrichment are primarily regulated by climatic factors, such as mean annual temperature (MAT) and mean annual precipitation (MAP), as well as the aridity index (AI) and N fertilizer application rates. Correlation analyses show that plant biomass is positively correlated with MAT, and tissue N content also exhibits a positive correlation with MAT. In contrast, nodule numbers and tissue N content are negatively correlated with N fertilizer application rates, whereas %Ndfa shows a positive correlation with AI and MAP. Under low N addition, the increase in total biomass in response to N enrichment is twice as large as that observed under high N addition. Furthermore, regions at lower elevations with abundant hydrothermal resources are especially favorable for total biomass accumulation, indicating that the responses of legumes to N enrichment are habitat-specific. These results provide scientific evidence for the mechanisms underlying legume responses to N enrichment and offer valuable insights and theoretical references for the conservation and management of legumes in the context of global climate change.

Effects of LAZY family genes on shoot gravitropism in Lotus japonicus

Plant architecture is an important agronomic trait to determine the biomass and sward structure of forage grass. The IGT family plays a pivotal role in plant gravitropism, encompassing both the gravitropic response and the modulation of plant architecture. We have previously shown that LjLAZY3, one of the IGT genes, plays a distinct role in root gravitropism in L. japonicus. However, the function of LAZY proteins on shoot gravitropism in this species is poorly understood. In this study, we identified nine IGT genes in the L. japonicus genome, which have been categorized into four clades based on the phylogenetic relationships of IGT proteins from 18 legumes: LAZY1, NGR (NEGATIVE GRAVITROPIC RESPONSE OF ROOTS), IGT-LIKE, and TAC1. We found that LAZY genes in the first three clades have demonstrated distinct role for modulating plant gravitropism in L. japonicus with specific impacts as follows. Mutation of the LAZY1 gene, LjLAZY1, defected the gravitropic response of hypocotyl without impacting the main stem's branch angle. In contrast, the overexpression of the NGR gene, LjLAZY3, substantially modulated the shoot's gravitropism, leading to narrower lateral branch angles. Additionally, it enhanced the shoots' gravitropic response. The overexpression of another NGR gene, LjLAZY4, specifically reduced the main stem's branch angle and decreased plant stature without affecting the shoot gravitropic response. The phenotype of IGT-LIKE gene LjLAZY2 overexpression is identical to that of LjLAZY4. While overexpression of the IGT-LIKE gene LjLAZY5 did not induce any observable changes in branch angle, plant height, or gravitropic response. Furthermore, the LjLAZYs were selectively interacted with different BRXL and RLD proteins, which should the important factor to determine their different functions in controlling organ architecture in L. japonicus. Our results deepen understanding of the LjLAZY family and its potential for plant architecture improvement in L. japonicus.

Conserved cis-elements enable NODULES WITH ACTIVATED DEFENSE1 regulation by NODULE INCEPTION during nodulation

Symbiotic nitrogen fixation within nitrogen-fixing clade (NFC) plants is thought to have arisen from a single gain followed by massive losses in the genomes of ancestral non-nodulating plants. However, molecular evidence supporting this model is limited. Here, we confirm through bioinformatic analysis that NODULES WITH ACTIVATED DEFENSE1 (NAD1) is present only in NFC plants and is thus an NFC-specific gene. Moreover, NAD1 was specifically expressed in nodules. We identified three conserved nodulation-associated cis-regulatory elements (NACE1-3) in the promoter of LjNAD1 from Lotus japonicus that are required for its nodule specific expression. A survey of NFC plants revealed that NACE1 and NACE2 are specific to the Fabales and Papilionoideae, respectively, while NACE3 is present in all NFC plants. Moreover, we found that nodule inception (NIN) directly binds to all three NACEs to activate NAD1 expression. Mutation of L. japonicus LjNAD1 resulted in the formation of abnormal symbiosomes with enlarged symbiosome space and frequent breakdown of bacteroids in nodules, resembling phenotypes reported for Medicago truncatula Mtnad1 and Mtnin mutants. These data point to NIN-NAD1 as an important module regulating rhizobial accommodation in nodules. The regulation of NAD1 by NIN in the NFC ancestor represent an important evolutionary adaptation for nodulation.

Duplication and sub-functionalization of flavonoid biosynthesis genes plays important role in Leguminosae root nodule symbiosis evolution

Gene innovation plays an essential role in trait evolution. Rhizobial symbioses, the most important N2-fixing agent in agricultural systems that exists mainly in Leguminosae, is one of the most attractive evolution events. However, the gene innovations underlying Leguminosae root nodule symbiosis (RNS) remain largely unknown. Here, we investigated the gene gain event in Leguminosae RNS evolution through comprehensive phylogenomic analyses. We revealed that Leguminosae-gain genes were acquired by gene duplication and underwent a strong purifying selection. Kyoto Encyclopedia of Genes and Genomes analyses showed that the innovated genes were enriched in flavonoid biosynthesis pathways, particular downstream of chalcone synthase (CHS). Among them, Leguminosae-gain type Ⅱ chalcone isomerase (CHI) could be further divided into CHI1A and CHI1B clades, which resulted from the products of tandem duplication. Furthermore, the duplicated CHI genes exhibited exon-intron structural divergences evolved through exon/intron gain/loss and insertion/deletion. Knocking down CHI1B significantly reduced nodulation in Glycine max (soybean) and Medicago truncatula; whereas, knocking down its duplication gene CHI1A had no effect on nodulation. Therefore, Leguminosae-gain type Ⅱ CHI participated in RNS and the duplicated CHI1A and CHI1B genes exhibited RNS functional divergence. This study provides functional insights into Leguminosae-gain genetic innovation and sub-functionalization after gene duplication that contribute to the evolution and adaptation of RNS in Leguminosae.

Bioinformatics Identification and Expression Analysis of Acetyl-CoA Carboxylase Reveal Its Role in Isoflavone Accumulation during Soybean Seed Development

Isoflavones belong to the class of flavonoid compounds, which are important secondary metabolites that play a crucial role in plant development and defense. Acetyl-CoA carboxylase (ACCase) is a biotin-dependent enzyme that catalyzes the conversion of Acetyl-CoA into Malonyl-CoA in plants. It is a key enzyme in fatty acid synthesis and also catalyzes the production of various secondary metabolites. However, information on the ACC gene family in the soybean (Glycine max L. Merr.) genome and the specific members involved in isoflavone biosynthesis is still lacking. In this study, we identified 20 ACC family genes (GmACCs) from the soybean genome and further characterized their evolutionary relationships and expression patterns. Phylogenetic analysis showed that the GmACCs could be divided into five groups, and the gene structures within the same groups were highly conserved, indicating that they had similar functions. The GmACCs were randomly distributed across 12 chromosomes, and collinearity analysis suggested that many GmACCs originated from tandem and segmental duplications, with these genes being under purifying selection. In addition, gene expression pattern analysis indicated that there was functional divergence among GmACCs in different tissues. The GmACCs reached their peak expression levels during the early or middle stages of seed development. Based on the transcriptome and isoflavone content data, a weighted gene co-expression network was constructed, and three candidate genes (Glyma.06G105900, Glyma.13G363500, and Glyma.13G057400) that may positively regulate isoflavone content were identified. These results provide valuable information for the further functional characterization and application of GmACCs in isoflavone biosynthesis in soybean.

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.

The Fabaceae in Northeastern Mexico (Subfamilies Caesalpinioideae (Excluding Tribe Mimoseae), Cercidoideae, and Detarioideae)

As part of the Fabaceae project of northeastern Mexico and based on field work, collection of botanical samples over the past 37 years, and reviewing botanical materials in national and international herbaria, the diversity of legumes of the subfamilies Caesalpinioideae (excluding tribe Mimoseae), Cercidoideae, and Detarioideae in northeastern Mexico has been recorded. New nomenclatural changes in tribes and genera of the subfamily Caesalpinioideae found in the new scientific bibliography are included. The subfamily Caesalpinioideae (excluding the tribe Mimoseae) includes five tribes: tribe Caesalpinieae, with eight genera (Caesalpinia, Coulteria, Denisophytum, Erythrostemon, Guilandina, Hoffmannseggia, Haematoxylum, and Pomaria) and 21 species; tribe Cassieae with three genera (Cassia, Chamaecrita, and Senna) and 28 species; tribe Ceratonieae with one genus (Ceratonia) and 1 species; tribe Gleditsieae with one genus (Gleditsia) and 1 species. The subfamily Cercidoideae includes two genera (Bauhinia and Cercis) and eight species, and the subfamily Detarioideae includes only one genus and one species (Tamarindus indicus). The total flora of these three subfamilies comprises 18 genera and 63 species, including 56 native species and 7 exotic ones: Bauhinia variegata, Cassia fistula, Ceratonia siliqua, Delonix regia, Erythrostemon gilliesii, Senna alata, and Tamarindus indicus. Endemism includes a total of 22 species and nine infraspecific categories.

The genome of Vicia sativa ssp. amphicarpa provides insights into the role of terpenoids in antimicrobial resistance within subterranean fruits

Vicia sativa ssp. amphicarpa is a unique forage crop capable of simultaneously producing fruits above and below ground, representing a typical amphicarpic plant. In this study, we sequenced and assembled seven pseudo-chromosomes of the genome of V. sativa ssp. amphicarpa (n = 7) yielding a genome size of 1.59 Gb, with a total annotation of 48 932 protein-coding genes. Long terminal repeat (LTR) elements constituted 62.28% of the genome, significantly contributing to the expansion of genome size. Phylogenetic analysis revealed that the divergence between V. sativa ssp. amphicarpa and V. sativa was around 0.88 million years ago (MYA). Comparative transcriptomic and metabolomic analysis of aerial and subterranean pod shells showed biosynthesis of terpenoids in the subterranean pod shells indicating a correlation between the antimicrobial activity of subterranean pod shells and the biosynthesis of terpenoids. Furthermore, functional validation indicates that overexpression of VsTPS5 and VsTPS16 enhances terpenoid biosynthesis for antibacterial activity. Metabolomic analysis suggests the involvement of terpenoids in the antimicrobial properties of subterranean pod shells. Deciphering the genome of V. sativa ssp. amphicarpa elucidated the molecular mechanisms behind the antimicrobial properties of subterranean fruits in amphicarpic plants, providing valuable insights for the study of amphicarpic plant biology.

Phosphorus-Use-Efficiency Gene Identification in Fabaceae and RSL2 Expansion in Lupinus albus Is Associated with Low-Phosphorus Adaptation

Phosphorus is critical for plant growth but often becomes less accessible due to its precipitation with cations in soil. Fabaceae, a diverse plant family, exhibits robust adaptability and includes species like Lupinus albus, known for its efficient phosphorus utilization via cluster roots. Here, we systematically identified phosphorus-utilization-efficiency (PUE) gene families across 35 Fabaceae species, highlighting significant gene amplification in PUE pathways in Fabaceae. Different PUE pathways exhibited variable amplification, evolution, and retention patterns among various Fabaceae crops. Additionally, the number of homologous genes of the root hair development gene RSL2 in L. albus was far more than that in other Fabaceae species. Multiple copies of the RSL2 gene were amplified and retained in L. albus after whole genome triplication. The gene structure and motifs specifically retained in L. albus were different from homologous genes in other plants. Combining transcriptome analysis under low-phosphorus treatment, it was found that most of the homologous genes of RSL2 in L. albus showed high expression in the cluster roots, suggesting that the RSL2 gene family plays an important role in the adaptation process of L. albus to low-phosphorus environments and the formation of cluster roots.

De novo genome assembly of white clover (Trifolium repens L.) reveals the role of copy number variation in rapid environmental adaptation

BACKGROUND

White clover (Trifolium repens) is a globally important perennial forage legume. This species also serves as an eco-evolutionary model system for studying within-species chemical defense variation; it features a well-studied polymorphism for cyanogenesis (HCN release following tissue damage), with higher frequencies of cyanogenic plants favored in warmer locations worldwide. Using a newly generated haplotype-resolved genome and two other long-read assemblies, we tested the hypothesis that copy number variants (CNVs) at cyanogenesis genes play a role in the ability of white clover to rapidly adapt to local environments. We also examined questions on subgenome evolution in this recently evolved allotetraploid species and on chromosomal rearrangements in the broader IRLC legume clade.

RESULTS

Integration of PacBio HiFi, Omni-C, Illumina, and linkage map data yielded a completely de novo genome assembly for white clover (created without a priori sequence assignment to subgenomes). We find that white clover has undergone extensive transposon diversification since its origin but otherwise shows highly conserved genome organization and composition with its diploid progenitors. Unlike some other clover species, its chromosomal structure is conserved with other IRLC legumes. We further find extensive evidence of CNVs at the major cyanogenesis loci; these contribute to quantitative variation in the cyanogenic phenotype and to local adaptation across wild North American populations.

CONCLUSIONS

This work provides a case study documenting the role of CNVs in local adaptation in a plant species, and it highlights the value of pan-genome data for identifying contributions of structural variants to adaptation in nature.

Host-imposed control mechanisms in legume-rhizobia symbiosis

Legumes are ecologically and economically important plants that contribute to nutrient cycling and agricultural sustainability, features tied to their intimate symbiosis with nitrogen-fixing rhizobia. Rhizobia vary dramatically in quality, ranging from highly growth-promoting to non-beneficial; therefore, legumes must optimize their symbiosis with rhizobia through host mechanisms that select for beneficial rhizobia and limit losses to non-beneficial strains. In this Perspective, we examine the considerable scientific progress made in decoding host control over rhizobia, empirically examining both molecular and cellular mechanisms and their effects on rhizobia symbiosis and its benefits. We consider pre-infection controls, which require the production and detection of precise molecular signals by the legume to attract and select for compatible rhizobia strains. We also discuss post-infection mechanisms that leverage the nodule-level and cell-level compartmentalization of symbionts to enable host control over rhizobia development and proliferation in planta. These layers of host control each contribute to legume fitness by directing host resources towards a narrowing subset of more-beneficial rhizobia.

Mapping the molecular landscape of Lotus japonicus nodule organogenesis through spatiotemporal transcriptomics

Legumes acquire nitrogen-fixing ability by forming root nodules. Transferring this capability to more crops could reduce our reliance on nitrogen fertilizers, thereby decreasing environmental pollution and agricultural production costs. Nodule organogenesis is complex, and a comprehensive transcriptomic atlas is crucial for understanding the underlying molecular events. Here, we utilized spatial transcriptomics to investigate the development of nodules in the model legume, Lotus japonicus. Our investigation has identified the developmental trajectories of two critical regions within the nodule: the infection zone and peripheral tissues. We reveal the underlying biological processes and provide gene sets to achieve symbiosis and material exchange, two essential aspects of nodulation. Among the candidate regulatory genes, we illustrate that LjNLP3, a transcription factor belonging to the NIN-LIKE PROTEIN family, orchestrates the transition of nodules from the differentiation to maturation. In summary, our research advances our understanding of nodule organogenesis and provides valuable data for developing symbiotic nitrogen-fixing crops.

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.

High-integrity Pueraria montana var. lobata genome and population analysis revealed the genetic diversity of Pueraria genus

Pueraria montana var. lobata (P. lobata) is a traditional medicinal plant belonging to the Pueraria genus of Fabaceae family. Pueraria montana var. thomsonii (P. thomsonii) and Pueraria montana var. montana (P. montana) are its related species. However, evolutionary history of the Pueraria genus is still largely unknown. Here, a high-integrity, chromosome-level genome of P. lobata and an improved genome of P. thomsonii were reported. It found evidence for an ancient whole-genome triplication and a recent whole-genome duplication shared with Fabaceae in three Pueraria species. Population genomics of 121 Pueraria accessions demonstrated that P. lobata populations had substantially higher genetic diversity, and P. thomsonii was probably derived from P. lobata by domestication as a subspecies. Selection sweep analysis identified candidate genes in P. thomsonii populations associated with the synthesis of auxin and gibberellin, which potentially play a role in the expansion and starch accumulation of tubers in P. thomsonii. Overall, the findings provide new insights into the evolutionary and domestication history of the Pueraria genome and offer a valuable genomic resource for the genetic improvement of these species.

Chromosome-level genome assembly and characterization of the Calophaca sinica genome

Calophaca sinica is a rare plant endemic to northern China which belongs to the Fabaceae family and possesses rich nutritional value. To support the preservation of the genetic resources of this plant, we have successfully generated a high-quality genome of C. sinica (1.06 Gb). Notably, transposable elements (TEs) constituted ~73% of the genome, with long terminal repeat retrotransposons (LTR-RTs) dominating this group of elements (~54% of the genome). The average intron length of the C. sinica genome was noticeably longer than what has been observed for closely related species. The expansion of LTR-RTs and elongated introns emerged had the largest influence on the enlarged genome size of C. sinica in comparison to other Fabaceae species. The proliferation of TEs could be explained by certain modes of gene duplication, namely, whole genome duplication (WGD) and dispersed duplication (DSD). Gene family expansion, which was found to enhance genes associated with metabolism, genetic maintenance, and environmental stress resistance, was a result of transposed duplicated genes (TRD) and WGD. The presented genomic analysis sheds light on the genetic architecture of C. sinica, as well as provides a starting point for future evolutionary biology, ecology, and functional genomics studies centred around C. sinica and closely related species.

Phylogenomic profiles of whole-genome duplications in Poaceae and landscape of differential duplicate retention and losses among major Poaceae lineages

Poaceae members shared a whole-genome duplication called rho. However, little is known about the evolutionary pattern of the rho-derived duplicates among Poaceae lineages and implications in adaptive evolution. Here we present phylogenomic/phylotranscriptomic analyses of 363 grasses covering all 12 subfamilies and report nine previously unknown whole-genome duplications. Furthermore, duplications from a single whole-genome duplication were mapped to multiple nodes on the species phylogeny; a whole-genome duplication was likely shared by woody bamboos with possible gene flow from herbaceous bamboos; and recent paralogues of a tetraploid Oryza are implicated in tolerance of seawater submergence. Moreover, rho duplicates showing differential retention among subfamilies include those with functions in environmental adaptations or morphogenesis, including ACOT for aquatic environments (Oryzoideae), CK2β for cold responses (Pooideae), SPIRAL1 for rapid cell elongation (Bambusoideae), and PAI1 for drought/cold responses (Panicoideae). This study presents a Poaceae whole-genome duplication profile with evidence for multiple evolutionary mechanisms that contribute to gene retention and losses.

Advances in Legume Systematics 14. Classification of Caesalpinioideae. Part 2: Higher-level classification

Caesalpinioideae is the second largest subfamily of legumes (Leguminosae) with ca. 4680 species and 163 genera. It is an ecologically and economically important group formed of mostly woody perennials that range from large canopy emergent trees to functionally herbaceous geoxyles, lianas and shrubs, and which has a global distribution, occurring on every continent except Antarctica. Following the recent re-circumscription of 15 Caesalpinioideae genera as presented in Advances in Legume Systematics 14, Part 1, and using as a basis a phylogenomic analysis of 997 nuclear gene sequences for 420 species and all but five of the genera currently recognised in the subfamily, we present a new higher-level classification for the subfamily. The new classification of Caesalpinioideae comprises eleven tribes, all of which are either new, reinstated or re-circumscribed at this rank: Caesalpinieae Rchb. (27 genera / ca. 223 species), Campsiandreae LPWG (2 / 5-22), Cassieae Bronn (7 / 695), Ceratonieae Rchb. (4 / 6), Dimorphandreae Benth. (4 / 35), Erythrophleeae LPWG (2 /13), Gleditsieae Nakai (3 / 20), Mimoseae Bronn (100 / ca. 3510), Pterogyneae LPWG (1 / 1), Schizolobieae Nakai (8 / 42-43), Sclerolobieae Benth. & Hook. f. (5 / ca. 113). Although many of these lineages have been recognised and named in the past, either as tribes or informal generic groups, their circumscriptions have varied widely and changed over the past decades, such that all the tribes described here differ in generic membership from those previously recognised. Importantly, the approximately 3500 species and 100 genera of the former subfamily Mimosoideae are now placed in the reinstated, but newly circumscribed, tribe Mimoseae. Because of the large size and ecological importance of the tribe, we also provide a clade-based classification system for Mimoseae that includes 17 named lower-level clades. Fourteen of the 100 Mimoseae genera remain unplaced in these lower-level clades: eight are resolved in two grades and six are phylogenetically isolated monogeneric lineages. In addition to the new classification, we provide a key to genera, morphological descriptions and notes for all 163 genera, all tribes, and all named clades. The diversity of growth forms, foliage, flowers and fruits are illustrated for all genera, and for each genus we also provide a distribution map, based on quality-controlled herbarium specimen localities. A glossary for specialised terms used in legume morphology is provided. This new phylogenetically based classification of Caesalpinioideae provides a solid system for communication and a framework for downstream analyses of biogeography, trait evolution and diversification, as well as for taxonomic revision of still understudied genera.

Haplotype-resolved genome of Mimosa bimucronata revealed insights into leaf movement and nitrogen fixation

BACKGROUND

Mimosa bimucronata originates from tropical America and exhibits distinctive leaf movement characterized by a relative slow speed. Additionally, this species possesses the ability to fix nitrogen. Despite these intriguing traits, comprehensive studies have been hindered by the lack of genomic resources for M. bimucronata.

RESULTS

To unravel the intricacies of leaf movement and nitrogen fixation, we successfully assembled a high-quality, haplotype-resolved, reference genome at the chromosome level, spanning 648 Mb and anchored in 13 pseudochromosomes. A total of 32,146 protein-coding genes were annotated. In particular, haplotype A was annotated with 31,035 protein-coding genes, and haplotype B with 31,440 protein-coding genes. Structural variations (SVs) and allele specific expression (ASE) analyses uncovered the potential role of structural variants in leaf movement and nitrogen fixation in M. bimucronata. Two whole-genome duplication (WGD) events were detected, that occurred ~ 2.9 and ~ 73.5 million years ago. Transcriptome and co-expression network analyses revealed the involvement of aquaporins (AQPs) and Ca2+-related ion channel genes in leaf movement. Moreover, we also identified nodulation-related genes and analyzed the structure and evolution of the key gene NIN in the process of symbiotic nitrogen fixation (SNF).

CONCLUSION

The detailed comparative genomic and transcriptomic analyses provided insights into the mechanisms governing leaf movement and nitrogen fixation in M. bimucronata. This research yielded genomic resources and provided an important reference for functional genomic studies of M. bimucronata and other legume species.

Out of Place: Phylogenomics resolves the placement of Eurasian taxa and sheds light on origin of Thermopsideae in North America

The North American Thermopsideae (Fabaceae: Papilionoideae), a monophyletic group comprising the North American endemic genus Baptisia, and the paraphyletic Eurasian-North American disjunct Thermopsis, is nested within the tribe Sophoreae. Previous phylogenetic studies have identified two East Asian taxa within the North American Thermopsideae, suggesting two independent dispersal events between North America-East Asia. More recent studies have also placed a third taxon, Vuralia turcica, an endemic species from Turkey, among the North American Thermopsideae. The presence of three geographically distant Eurasian taxa within a relatively young clade of North American origin is unprecedented among papilionoid legumes, and the biogeographic implications of this observation are not clear. To investigate this matter, 1540 low-copy nuclear genes and complete plastomes were obtained from 36 taxa across the core genistoids, including 26 newly sequenced taxa. Nuclear and plastome based maximum likelihood (ML) and ASTRAL analyses were conducted based on varying degrees of taxon coverage and read mapping consensus threshold values. Additional analyses were performed to estimate divergence times and to reconstruct biogeographic history. The results strongly support a previously undetected Old World clade, presently composed of V. turcica and T. chinensis, which diverged from the ancestor of the North American lineage during the mid to late Miocene. A single and recent North America-East Asia dispersal involving T. lupinoides is reported. Furthermore, the traditional inclusion of the genus Ammopiptanthus among Thermopsideae is not supported, and the monotypic generic status of Vuralia is called into question. A relatively high degree of cytonuclear discordance is reported within each sub-clade of the North American Thermopsideae. This finding is likely attributable to the high degree of interspecific hybridization reported within these groups and raises the need for more rigorous genome-scale testing to better delimit species within each of the reticulating subclades. Subjects: Biodiversity, Biogeography, Evolutionary Studies, Genetics, Plant Science.

Haplotype-resolved genome assembly of Phanera championii reveals molecular mechanisms of flavonoid synthesis and adaptive evolution

Phanera championii is a medicinal liana plant that has successfully adapted to hostile karst habitats. Despite extensive research on its medicinal components and pharmacological effects, the molecular mechanisms underlying the biosynthesis of critical flavonoids and its adaptation to karst habitats remain elusive. In this study, we performed high-coverage PacBio and Hi-C sequencing of P. championii, which revealed its high heterozygosity and phased the genome into two haplotypes: Hap1 (384.60 Mb) and Hap2 (383.70 Mb), encompassing a total of 58 612 annotated genes. Comparative genomes analysis revealed that P. championii experienced two whole-genome duplications (WGDs), with approximately 59.59% of genes originating from WGD events, thereby providing a valuable genetic resource for P. championii. Moreover, we identified a total of 112 genes that were strongly positively selected. Additionally, about 81.60 Mb of structural variations between the two haplotypes. The allele-specific expression patterns suggested that the dominant effect of P. championii was the elimination of deleterious mutations and the promotion of beneficial mutations to enhance fitness. Moreover, our transcriptome and metabolome analysis revealed alleles in different tissues or different haplotypes collectively regulate the synthesis of flavonoid metabolites. In summary, our comprehensive study highlights the significance of genomic and morphological adaptation in the successful adaptation of P. championii to karst habitats. The high-quality phased genomes obtained in this study serve as invaluable genomic resources for various applications, including germplasm conservation, breeding, evolutionary studies, and elucidation of pathways governing key biological traits of P. championii.

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.

Advances in pharmacology, biosynthesis, and metabolic engineering of Scutellaria-specialized metabolites

Scutellaria Linn., which belongs to the family Lamiaceae, is a commonly used medicinal plant for heat clearing and detoxification. In particular, the roots of S. baicalensis and the entire herb of S. barbata have been widely used in traditional medicine for thousands of years. The main active components of Scutellaria, including: baicalein, wogonin, norwogonin, scutellarein, and their glycosides have potential or existing drug usage. However, the wild resources of Scutellaria plants have been overexploited, and degenerated germplasm resources cannot fulfill the requirements of chemical extraction and clinical usage. Metabolic engineering and green production via microorganisms provide alternative strategies for greater efficiency in the production of natural products. Here, we review the progress of: pharmacological investigations, multi-omics, biosynthetic pathways, and metabolic engineering of various Scutellaria species and their active compounds. In addition, based on multi-omics data, we systematically analyze the phylogenetic relationships of Scutellaria and predict candidate transcription factors related to the regulation of active flavonoids. Finally, we propose the prospects of directed evolution of core enzymes and genome-assisted breeding to alleviate the shortage of plant resources of Scutellaria. This review provides important insights into the sustainable utilization and development of Scutellaria resources.

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.

Whole Genome Duplication Events Likely Contributed to the Aquatic Adaptive Evolution of Parkerioideae

As the only aquatic lineage of Pteridaceae, Parkerioideae is distinct from many xeric-adapted species of the family and consists of the freshwater Ceratopteris species and the only mangrove ferns from the genus Acrostichum. Previous studies have shown that whole genome duplication (WGD) has occurred in Parkerioideae at least once and may have played a role in their adaptive evolution; however, more in-depth research regarding this is still required. In this study, comparative and evolutionary transcriptomics analyses were carried out to identify WGDs and explore their roles in the environmental adaptation of Parkerioideae. Three putative WGD events were identified within Parkerioideae, two of which were specific to Ceratopteris and Acrostichum, respectively. The functional enrichment analysis indicated that the lineage-specific WGD events have played a role in the adaptation of Parkerioideae to the low oxygen concentrations of aquatic habitats, as well as different aquatic environments of Ceratopteris and Acrostichum, such as the adaptation of Ceratopteris to reduced light levels and the adaptation of Acrostichum to high salinity. Positive selection analysis further provided evidence that the putative WGD events may have facilitated the adaptation of Parkerioideae to changes in habitat. Moreover, the gene family analysis indicated that the plasma membrane H+-ATPase (AHA), vacuolar H+-ATPase (VHA), and suppressor of K+ transport growth defect 1 (SKD1) may have been involved in the high salinity adaptation of Acrostichum. Our study provides new insights into the evolution and adaptations of Parkerioideae in different aquatic environments.

Genome-Wide Identification of the Paulownia fortunei Aux/IAA Gene Family and Its Response to Witches' Broom Caused by Phytoplasma

The typical symptom of Paulownia witches' broom (PaWB), caused by phytoplasma infection, is excessive branching, which is mainly triggered by auxin metabolism disorder. Aux/IAA is the early auxin-responsive gene that participates in regulating plant morphogenesis such as apical dominance, stem elongation, lateral branch development, and lateral root formation. However, no studies have investigated the response of the Aux/IAA gene family to phytoplasma infection in Paulownia fortunei. In this study, a total of 62 Aux/IAA genes were found in the genome. Phylogenetic analysis showed that PfAux/IAA genes could be divided into eight subgroups, which were formed by tandem duplication and fragment replication. Most of them had a simple gene structure, and several members lacked one or two conserved domains. By combining the expression of PfAux/IAA genes under phytoplasma stress and SA-treated phytoplasma-infected seedlings, we found that PfAux/IAA13/33/45 may play a vital role in the occurrence of PaWB. Functional analysis based on homologous relationships showed a strong correlation between PfAux/IAA45 and branching. Protein-protein interaction prediction showed that PfARF might be the binding partner of PfAux/IAA, and the yeast two-hybrid assay and bimolecular fluorescent complementary assay confirmed the interaction of PfAux/IAA45 and PfARF13. This study provides a theoretical basis for further understanding the function of the PfAux/IAA gene family and exploring the regulatory mechanism of branching symptoms caused by PaWB.

Characteristics of chloroplast and mitochondrial genomes and intracellular gene transfer in the Korean endemic shrub, Sophora koreensis Nakai (Fabaceae)

Sophora koreensis Nakai, an endemic species distributed only in the Korean Peninsula, is of great geographical, economic, and taxonomic importance. Although its complete chloroplast (cp) genome sequence has been reported, its mitochondrial (mt) genome sequence has not yet been studied. Therefore, in this study, we aimed to investigate its mt genome sequence and compare it with those reported for other Fabaceae species. Total genomic DNA was extracted from fresh S. koreensis leaves collected from natural habitats in Gangwon-do Province, South Korea. This was followed by polymerase chain reaction (PCR) amplification of cpDNA insertions in the mt genome and the detection of microsatellites and dispersed repeats in the cp and mt genomes. Finally, the cp and mt genomes of S. koreensis were compared with those reported for other Fabaceae species. The cp sequence of S. koreensis showed identical gene orders and contents as those previously reported. Only six substitutions and one deletion were detected with 99 % homology. Conversely, the complete mt genome sequence, which was 517,845 bp in length and encoded 61 genes, including 43 protein-coding, 15 transfer RNAs, and 3 ribosomal RNA genes, was considerably different from that of S. japonica in terms of gene order and composition. Further, the mt genome of S. koreensis included ca. 7 and 3 kb insertions, representing an intracellular gene transfer (IGT) event, and the regions with these insertions were determined to be originally present in the cp genome. This IGT event was also confirmed via PCR amplification. IGT events can be induced via biological gene expression control or the use of repetitive sequences, and they provide important insights into the evolutionary lineage of S. koreensis. However, further studies are needed to clarify the gene transfer mechanisms between the two organelles.

The Fabaceae in Northeastern Mexico (Subfamily Caesalpinioideae, Mimosoideae Clade, Tribes Mimoseae, Acacieae, and Ingeae)

A synoptic compendium of the legumes of the Mimosoideae clade in northeastern Mexico is presented for the first time, including changes in their botanical nomenclature and retypification of genera. Furthermore, based on new information recently published, the taxonomic limits of several new genera segregated from Acacia (Acaciella, Mariosousa, Senegalia, and Vachellia) and Prosopis (Neltuma and Strombocarpa) are clarified and included. Based on field work, collection of botanical samples over the past 30 years, and reviewing botanical materials in national and international herbaria, we have completed the diversity of legumes of the Mimosoideae clade of northeastern Mexico. Three tribes (Acacieae, Ingeae, and Mimosaeae), 22 genera, 92 species, and 19 infraspecific categories were recorded. Only the genus Painteria is endemic to Mexico. Eighty-eight species are native to Mexico, and four are exotic: Acacia salicina, Neptunia prostrata, Neltuma chilensis and Albizia lebbeck. Twenty-eight species are endemic to Mexico, nine species are endemic to northeastern Mexico, and four species are endemic to only one state in Mexico. The 22 registered genera represent 44% and 65% of the generic flora of the Mimosoideae clade for Mexico and the planet, respectively, while the 92 species registered represent 3% and 18% of the species of the clade Mimosoideae for the planet and Mexico, respectively. According to the new nomenclature of legumes, the number of genera in the Mimosoideae clade in northern Mexico has increased from 19 to 24.

The complete mitochondrial genome of Bauhinia variegata (Leguminosae)

The mitogenome of Bauhinia variegate was assembled and characterized in this study. The mitogenome size was 437,271 bp, and its GC content was 45.5%. 36 protein-coding genes, 17 tRNAs and 3 rRNAs were annotated in the mitogenome. A total of 12 MTPTs, ranging from 71 bp to 3562 bp, were identified in the mitogenome and covered 1.46% (6373 bp) of the mitogenome. Phylogenetic analysis of 15 species of Leguminosae based on 23 core protein-coding genes showed that B. variegata was sister to Tylosema esculentum, another member from the subfamily Cercidoideae. The mitogenome of B. variegata provides a valuable genetic resource for further phylogenetic studies of this family.

Identification and Expression Analysis of the Nucleotidyl Transferase Protein (NTP) Family in Soybean (Glycine max) under Various Abiotic Stresses

Nucleotidyl transferases (NTPs) are common transferases in eukaryotes and play a crucial role in nucleotide modifications at the 3' end of RNA. In plants, NTPs can regulate RNA stability by influencing 3' end modifications, which in turn affect plant growth, development, stress responses, and disease resistance. Although the functions of NTP family members have been extensively studied in Arabidopsis, rice, and maize, there is limited knowledge about NTP genes in soybeans. In this study, we identified 16 members of the NTP family in soybeans, including two subfamilies (G1 and G2) with distinct secondary structures, conserved motifs, and domain distributions at the protein level. Evolutionary analysis of genes in the NTP family across multiple species and gene collinearity analysis revealed a relatively conserved evolutionary pattern. Analysis of the tertiary structure of the proteins showed that NTPs have three conserved aspartic acids that bind together to form a possible active site. Tissue-specific expression analysis indicated that some NTP genes exhibit tissue-specific expression, likely due to their specific functions. Stress expression analysis showed significant differences in the expression levels of NTP genes under high salt, drought, and cold stress. Additionally, RNA-seq analysis of soybean plants subjected to salt and drought stress further confirmed the association of soybean NTP genes with abiotic stress responses. Subcellular localization experiments revealed that GmNTP2 and GmNTP14, which likely have similar functions to HESO1 and URT1, are located in the nucleus. These research findings provide a foundation for further investigations into the functions of NTP family genes in soybeans.

Comparative phylogenomics and phylotranscriptomics provide insights into the genetic complexity of nitrogen-fixing root-nodule symbiosis

Plant root-nodule symbiosis (RNS) with mutualistic nitrogen-fixing bacteria is restricted to a single clade of angiosperms, the Nitrogen-Fixing Nodulation Clade (NFNC), and is best understood in the legume family. Nodulating species share many commonalities, explained either by divergence from a common ancestor over 100 million years ago or by convergence following independent origins over that same time period. Regardless, comparative analyses of diverse nodulation syndromes can provide insights into constraints on nodulation-what must be acquired or cannot be lost for a functional symbiosis-and the latitude for variation in the symbiosis. However, much remains to be learned about nodulation, especially outside of legumes. Here, we employed a large-scale phylogenomic analysis across 88 species, complemented by 151 RNA-seq libraries, to elucidate the evolution of RNS. Our phylogenomic analyses further emphasize the uniqueness of the transcription factor NIN as a master regulator of nodulation and identify key mutations that affect its function across the NFNC. Comparative transcriptomic assessment revealed nodule-specific upregulated genes across diverse nodulating plants, while also identifying nodule-specific and nitrogen-response genes. Approximately 70% of symbiosis-related genes are highly conserved in the four representative species, whereas defense-related and host-range restriction genes tend to be lineage specific. Our study also identified over 900 000 conserved non-coding elements (CNEs), over 300 000 of which are unique to sampled NFNC species. NFNC-specific CNEs are enriched with the active H3K9ac mark and are correlated with accessible chromatin regions, thus representing a pool of candidate regulatory elements for genes involved in RNS. Collectively, our results provide novel insights into the evolution of nodulation and lay a foundation for engineering of RNS traits in agriculturally important crops.

Probiotic model for studying rhizosphere interactions of root exudates and the functional microbiome

Root exudates are important mediators of plant-microbiome interactions. Recent pioneering studies on various aerial root plants, including cereals, have shown that carbohydrate-rich mucilage can enrich diazotrophs and increase host nitrogen utilization and growth. Moreover, non-diazotrophic "gatekeeper" microorganisms in mucilage help defend against pathogenic and environmental microbes. These findings highlight the active role of root exudates in mediating plant-microbiome interactions to maintain microbial homeostasis in the rhizosphere. However, little is known about the specific mechanisms by which root exudates modulate the functional microbiome and homeostasis in rhizosphere microhabitats. Here, we propose the typical and stable biointeractions of four plant-specific aerial root mucilage-probiotic systems as a model for understanding root exudate-functional microbiome interaction. We anticipate that this model can provide fundamental biological insights into rhizosphere interactions.

The genomes of 5 underutilized Papilionoideae crops provide insights into root nodulation and disease resistance

BACKGROUND

The Papilionoideae subfamily contains a large amount of underutilized legume crops, which are important for food security and human sustainability. However, the lack of genomic resources has hindered the breeding and utilization of these crops.

RESULTS

Here, we present chromosome-level reference genomes for 5 underutilized diploid Papilionoideae crops: sword bean (Canavalia gladiata), scarlet runner bean (Phaseolus coccineus), winged bean (Psophocarpus tetragonolobus), smooth rattlebox (Crotalaria pallida), and butterfly pea (Clitoria ternatea), with assembled genome sizes of 0.62 Gb, 0.59 Gb, 0.71 Gb, 1.22 Gb, and 1.72 Gb, respectively. We found that the long period of higher long terminal repeat retrotransposon activity is the major reason that the genome size of smooth rattlebox and butterfly pea is enlarged. Additionally, there have been no recent whole-genome duplication (WGD) events in these 5 species except for the shared papilionoid-specific WGD event (∼55 million years ago). Then, we identified 5,328 and 10,434 species-specific genes between scarlet runner bean and common bean, respectively, which may be responsible for their phenotypic and functional differences and species-specific functions. Furthermore, we identified the key genes involved in root-nodule symbiosis (RNS) in all 5 species and found that the NIN gene was duplicated in the early Papilionoideae ancestor, followed by the loss of 1 gene copy in smooth rattlebox and butterfly pea lineages. Last, we identified the resistance (R) genes for plant defenses in these 5 species and characterized their evolutionary history.

CONCLUSIONS

In summary, this study provides chromosome-scale reference genomes for 3 grain and vegetable beans (sword bean, scarlet runner bean, winged bean), along with genomes for a green manure crop (smooth rattlebox) and a food dyeing crop (butterfly pea). These genomes are crucial for studying phylogenetic history, unraveling nitrogen-fixing RNS evolution, and advancing plant defense research.

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.

Phylogenomic Analyses Reveal an Allopolyploid Origin of Core Didymocarpinae (Gesneriaceae) Followed by Rapid Radiation

Allopolyploid plants have long been regarded as possessing genetic advantages under certain circumstances due to the combined effects of their hybrid origins and duplicated genomes. However, the evolutionary consequences of allopolyploidy in lineage diversification remain to be fully understood. Here, we investigate the evolutionary consequences of allopolyploidy using 138 transcriptomic sequences of Gesneriaceae, including 124 newly sequenced, focusing particularly on the largest subtribe Didymocarpinae. We estimated the phylogeny of Gesneriaceae using concatenated and coalescent-based methods based on five different nuclear matrices and 27 plastid genes, focusing on relationships among major clades. To better understand the evolutionary affinities in this family, we applied a range of approaches to characterize the extent and cause of phylogenetic incongruence. We found that extensive conflicts between nuclear and chloroplast genomes and among nuclear genes were caused by both incomplete lineage sorting (ILS) and reticulation, and we found evidence of widespread ancient hybridization and introgression. Using the most highly supported phylogenomic framework, we revealed multiple bursts of gene duplication throughout the evolutionary history of Gesneriaceae. By incorporating molecular dating and analyses of diversification dynamics, our study shows that an ancient allopolyploidization event occurred around the Oligocene-Miocene boundary, which may have driven the rapid radiation of core Didymocarpinae.

Parallel selection of loss-of-function alleles of Pdh1 orthologous genes in warm-season legumes for pod indehiscence and plasticity is related to precipitation

Pod dehiscence facilitates seed dispersal in wild legumes but results in yield loss in cultivated legumes. The evolutionary genetics of the legume pod dehiscence trait remain largely elusive. We characterized the pod dehiscence of chromosome segment substitution lines of Glycine max crossed with Glycine soja and found that the gene underlying the predominant quantitative trait locus (QTL) of soybean pod-shattering trait was Pod dehiscence 1 (Pdh1). A few rare loss-of-function (LoF) Pdh1 alleles were identified in G. soja, while only an allele featuring a premature stop codon was selected for pod indehiscence in cultivated soybean and spread to low-precipitation regions with increased frequency. Moreover, correlated interactions among Pdh1's haplotype, gene expression, and environmental changes for the developmental plasticity of the pod dehiscence trait were revealed in G. max. We found that orthologous Pdh1 genes specifically originated in warm-season legumes and their LoF alleles were then parallel-selected during the domestication of legume crops. Our results provide insights into the convergent evolution of pod dehiscence in warm-season legumes, facilitate an understanding of the intricate interactions between genetic robustness and environmental adaptation for developmental plasticity, and guide the breeding of new legume varieties with pod indehiscence.

The complete plastid genome sequence of Lysidice brevicalyx (Fabaceae: Detarioideae), an arbor species endemic to China

The plastid genome of Lysidice brevicalyx was successfully assembled using Illumina sequencing reads for the first time. The complete plastid genome of L. brevicalyx is a circular structure of 159,084 bp with a GC content of 36.4%. It comprises a large single-copy (LSC) region of 87,783 bp, a small single-copy (SSC) region of 19,557 bp, and two inverted repeat regions (IRA and IRB) of 25,872 bp, each. The plastome of L. brevicalyx contains a total of 128 genes, including 83 protein-coding genes, 37 tRNAs, and 8 rRNAs. The phylogenetic analysis strongly supports the monophyly of Lysidice. This study provides the first complete plastid genome sequence of L. brevicalyx and contributes to our understanding of the molecular characteristics and evolutionary relationships of this plant species.

Interploidy Introgression Shaped Adaptation during the Origin and Domestication History of Brassica napus

Polyploidy is recurrent across the tree of life and known as an evolutionary driving force in plant diversification and crop domestication. How polyploid plants adapt to various habitats has been a fundamental question that remained largely unanswered. Brassica napus is a major crop cultivated worldwide, resulting from allopolyploidy between unknown accessions of diploid B. rapa and B. oleracea. Here, we used whole-genome resequencing data of accessions representing the majority of morphotypes and ecotypes from the species B. rapa, B. oleracea, and B. napus to investigate the role of polyploidy during domestication. To do so, we first reconstructed the phylogenetic history of B. napus, which supported the hypothesis that the emergence of B. napus derived from the hybridization of European turnip of B. rapa and wild B. oleracea. These analyses also showed that morphotypes of swede and Siberian kale (used as vegetable and fodder) were domesticated before rapeseed (oil crop). We next observed that frequent interploidy introgressions from sympatric diploids were prominent throughout the domestication history of B. napus. Introgressed genomic regions were shown to increase the overall genetic diversity and tend to be localized in regions of high recombination. We detected numerous candidate adaptive introgressed regions and found evidence that some of the genes in these regions contributed to phenotypic diversification and adaptation of different morphotypes. Overall, our results shed light on the origin and domestication of B. napus and demonstrate interploidy introgression as an important mechanism that fuels rapid diversification in polyploid species.

Chromosome-level genome assembly and population genomics of Robinia pseudoacacia reveal the genetic basis for its wide cultivation

Urban greening provides important ecosystem services and ideal places for urban recreation and is a serious consideration for municipal decision-makers. Among the tree species cultivated in urban green spaces, Robinia pseudoacacia stands out due to its attractive flowers, fragrances, high trunks, wide adaptability, and essential ecosystem services. However, the genomic basis and consequences of its wide-planting in urban green spaces remains unknown. Here, we report the chromosome-level genome assembly of R. pseudoacacia, revealing a genome size of 682.4 Mb and 33,187 protein-coding genes. More than 99.3% of the assembly is anchored to 11 chromosomes with an N50 of 59.9 Mb. Comparative genomic analyses among 17 species reveal that gene families related to traits favoured by urbanites, such as wood formation, biosynthesis, and drought tolerance, are notably expanded in R. pseudoacacia. Our population genomic analyses further recover 11 genes that are under recent selection. Ultimately, these genes play important roles in the biological processes related to flower development, water retention, and immunization. Altogether, our results reveal the evolutionary forces that shape R. pseudoacacia cultivated for urban greening. These findings also present a valuable foundation for the future development of agronomic traits and molecular breeding strategies for R. pseudoacacia.

Lineage-specific amplification and epigenetic regulation of LTR-retrotransposons contribute to the structure, evolution, and function of Fabaceae species

BACKGROUND

Long terminal repeat (LTR)-retrotransposons (LTR-RTs) are ubiquitous and make up the majority of nearly all sequenced plant genomes, whereas their pivotal roles in genome evolution, gene expression regulation as well as their epigenetic regulation are still not well understood, especially in a large number of closely related species.

RESULTS

Here, we analyzed the abundance and dynamic evolution of LTR-RTs in 54 species from an economically and agronomically important family, Fabaceae, and also selected two representative species for further analysis in expression of associated genes, transcriptional activity and DNA methylation patterns of LTR-RTs. Annotation results revealed highly varied proportions of LTR-RTs in these genomes (5.1%~68.4%) and their correlation with genome size was highly positive, and they were significantly contributed to the variance in genome size through species-specific unique amplifications. Almost all of the intact LTR-RTs were inserted into the genomes 4 Mya (million years ago), and more than 50% of them were inserted in the last 0.5 million years, suggesting that recent amplifications of LTR-RTs were an important force driving genome evolution. In addition, expression levels of genes with intronic, promoter, and downstream LTR-RT insertions of Glycine max and Vigna radiata, two agronomically important crops in Fabaceae, showed that the LTR-RTs located in promoter or downstream regions suppressed associated gene expression. However, the LTR-RTs within introns promoted gene expression or had no contribution to gene expression. Additionally, shorter and younger LTR-RTs maintained higher mobility and transpositional potential. Compared with the transcriptionally silent LTR-RTs, the active elements showed significantly lower DNA methylation levels in all three contexts. The distributions of transcriptionally active and silent LTR-RT methylation varied across different lineages due to the position of LTR-RTs located or potentially epigenetic regulation.

CONCLUSION

Lineage-specific amplification patterns were observed and higher methylation level may repress the activity of LTR-RTs, further influence evolution in Fabaceae species. This study offers valuable clues into the evolution, function, transcriptional activity and epigenetic regulation of LTR-RTs in Fabaceae genomes.