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Abstract Tandem repeats (TRs) are genomic regions that tandemly change in repeat number, which are often multiallelic. Their characteristics and contributions to gene expression and quantitative traits in rice are largely unknown. Here, we survey rice TR variations based on 231 genome assemblies and the rice pan-genome graph. We identify 227,391 multiallelic TR loci, including 54,416 TR variations that are absent from the Nipponbare reference genome. Only 1/3 TR variations show strong linkage with nearby bi-allelic variants (SNPs, Indels and PAVs). Using 193 panicle and 202 leaf transcriptomic data, we reveal 485 and 511 TRs act as QTLs independently of other bi-allelic variations to nearby gene expression, respectively. Using plant height and grain width as examples, we identify and validate TRs contributions to rice agronomic trait variations. These findings would enhance our understanding of the functions of multiallelic variants and facilitate rice molecular breeding.

Abstract Background Tartary buckwheat (Fagopyrum tataricum) is an important food and medicine crop plant, which has been cultivated for 4000 years. A nuclear genome has been generated for this species, while an intraspecific pan-plastome has yet to be produced. As such a detailed understanding of the maternal genealogy of Tartary buckwheat has not been thoroughly investigated. Results In this study, we de novo assembled 513 complete plastomes of Fagopyrum and compared with 8 complete plastomes of Fagopyrum downloaded from the NCBI database to construct a pan-plastome for F. tartaricum and resolve genomic variation. The complete plastomes of the 513 newly assembled Fagopyrum plastome sizes ranged from 159,253 bp to 159,576 bp with total GC contents ranged from 37.76 to 37.97%. These plastomes all maintained the typical quadripartite structure, consisting of a pair of inverted repeat regions (IRA and IRB) separated by a large single copy region (LSC) and a small single copy region (SSC). Although the structure and gene content of the Fagopyrum plastomes are conserved, numerous nucleotide variations were detected from which population structure could be resolved. The nucleotide variants were most abundant in the non-coding regions of the genome and of those the intergenic regions had the most. Mutational hotspots were primarily found in the LSC regions. The complete 521 Fagopyrum plastomes were divided into five genetic clusters, among which 509 Tartary buckwheat plastomes were divided into three genetic clusters (Ft-I/Ft-II/Ft-III). The genetic diversity in the Tartary buckwheat genetic clusters was the greatest in Ft-III, and the genetic distance between Ft-I and Ft-II was the largest. Based on the results of population structure and genetic diversity analysis, Ft-III was further subdivided into three subgroups Ft-IIIa, Ft-IIIb, and Ft-IIIc. Divergence time estimation indicated that the genera Fagopyrum and Rheum (rhubarb) shared a common ancestor about 48 million years ago (mya) and that intraspecies divergence in Tartary buckwheat began around 0.42 mya. Conclusions The resolution of pan-plastome diversity in Tartary buckwheat provides an important resource for future projects such as marker-assisted breeding and germplasm preservation.

Lagerstroemia L. (Lythraceae) is a widely distributed genus of trees and shrubs native to tropical and subtropical environments from Southeast Asia to Australia, with numerous species highly valued as ornamentals. Although the plastomes of many species in this genus have been sequenced, the rates of functional gene evolution and their effect on phylogenetic analyses have not been thoroughly examined. We compared three plastome sequence matrices to elucidate how differences in these datasets affected phylogenetic analyses. Robust phylogenetic relationships for Lagerstroemia species were reconstructed based on different plastome sequence partitions and multiple phylogenetic methods. Identification of single-nucleotide variants within different genes also provides basic data on the patterns of functional gene evolution in Lagerstroemia and may provide insights into how those mutations affect protein structure and potentially drive divergence via cytonuclear incompatibility. These results as well as analyses of non-synonymous and synonymous mutations, indicate that heterotachic modes of evolution are present in functional plastome genes and should be accounted for in the analyses of molecular evolution. In addition, divergence events within the Lagerstroemia were dated for the first time. Several of the divergence estimates corresponded to well-known Earth history events, such as the reduction in global temperatures at the Eocene/Oligocene boundary. Our analyses conducted in Lagerstroemia here dissects the various patterns in the divergence of Lagerstroemia and may provide a useful guide to help plant breeders, as well as the necessity of using plastomic data and as possible as to combine evidence from morphological characteristics to investigate the complicated interspecies relationship and the evolutionary dynamics of species.

Abstract Background Mitochondria are organelles within eukaryotic cells that are central to the metabolic processes of cellular respiration and ATP production. However, the evolution of mitochondrial genomes (mitogenomes) in plants is virtually unknown compared to animal mitogenomes or plant plastids, due to complex structural variation and long stretches of repetitive DNA making accurate genome assembly more challenging. Comparing the structural and sequence differences of organellar genomes within and between sorghum species is an essential step in understanding evolutionary processes such as organellar sequence transfer to the nuclear genome as well as improving agronomic traits in sorghum related to cellular metabolism. Results Here, we assembled seven sorghum mitochondrial and plastid genomes and resolved reticulated mitogenome structures with multilinked relationships that could be grouped into three structural conformations that differ in the content of repeats and genes by contig. The grouping of these mitogenome structural types reflects the two domestication events for sorghum in east and west Africa. Conclusions We report seven mitogenomes of sorghum from different cultivars and wild sources. The assembly method used here will be helpful in resolving complex genomic structures in other plant species. Our findings give new insights into the structure of sorghum mitogenomes that provides an important foundation for future research into the improvement of sorghum traits related to cellular respiration, cytonuclear incompatibly, and disease resistance.

The Asian lotus (Nelumbo nucifera) has a history of cultivation in Asia dating back over 3,000 years where it has been an important food crop producing edible rhizomes and seeds as well as flowers of great aesthetic and cultural value. Here, we de novo assembled the plastomes of 316 lotus accessions including five North American lotus (N. lutea) and 311 Asian lotus (N. nucifera) to construct a pan-plastome genome map, and investigate the phylogeography and genetic diversity among the only two extant species within this living fossil lineage. A total of 113 unique genes were annotated and plastome sizes varied between 163,457 and 163,672 bp with only minor differences in each of the four major genomic units. The most abundant nucleotide differences among plastomes were single nucleotide variants followed by insertions/deletions and block substitutions mainly found in intergenic spacer regions of the large single copy portion of the plastome. Seven well-supported genetic clusters were resolved using multiple different population structure analyses. The different lotus types (flower, seed, rhizome, or wild) were disproportionally assigned to multiple different genetic clusters. This pattern indicates that the domestication of Asian lotus involved multiple genetic origins and possible matrilineal introgression. Geographic mapping of accessions also revealed that genetic diversity is unevenly distributed with eastern China possessing the highest genetic diversity and regions such as Yunnan, Indonesian, and Thailand possessing unique haplotypes. These results provide an important maternal history of Nelumbo and necessary groundwork for future studies on intergenomic gene transfer, cytonuclear incompatibility, and conservation genetics.

Bread wheat (Triticum aestivum L.) is one of the most extensively cultivated cereal crops around the world. Here, we investigated the population structure and genetic diversity of a panel mainly originated from two wheat agro-ecological regions (northern winter wheat region, NW; and the Huang-Huai River Valley’s facultative wheat region, HH) in China based on a 15K SNP array. Population genetic analysis revealed that the optimal population number (K) was three, and the three groups were roughly related to ecological regions, including NW (mainly Hebei), HH1 (Henan-Shaanxi), and HH2 (Shandong). Within HH, HH1 had a higher nucleotide diversity (π = 0.31167), minor allele frequency (MAF = 0.2663), polymorphism information content (PIC = 0.2668), and expected heterozygosity (Hexp = 0.3346) than HH2. Furthermore, our results demonstrated that genetic diversity decreases with the advancement of wheat breeding. Finally, inference of ancestry informative markers indicated that the genomes of the three pure groups from the three provinces (Hebei, Henan, and Shandong) of the two regions have genomic regions with different mosaic patterns derived from the two landrace groups. These findings may facilitate the development of wheat breeding strategies to target novel desired alleles in the future.

Abstract Cytoplasmic male sterility (CMS) is a widely used genetic tool in modern hybrid rice breeding. Most genes conferring rice gametophytic CMS are homologous to orf79 and co‐transcribe with atp6. However, the origin, differentiation and flow of these mitochondrial genes in wild and cultivated rice species remain unclear. In this study, we performed de novo assembly of the mitochondrial genomes of 221 common wild rice (Oryza rufipogon Griff.) and 369 Asian cultivated rice (Oryza sativa L.) accessions, and identified 16 haplotypes of atp6‐orf79‐like structures and 11 orf79 alleles. These homologous structures were classified into 4 distinct groups (AO‐I, AO‐II, AO‐III and AO‐IV), all of which were observed in O. rufipogon but only AO‐I was detected in O. sativa, causing a decrease in the frequency of atp6‐orf79‐like structures from 19.9% to 8.1%. Phylogenetic and biogeographic analyses revealed that the different groups of these gametophytic CMS‐related genes in O. rufipogon evolved in a multicentric pattern. The geographical origin of the atp6‐orf79‐like structures was further traced back, and a candidate region in north‐east of Gangetic Plain on the Indian Peninsula (South Asia) was identified as the origin centre of AO‐I. The orf79 alleles were detected in all three cytoplasmic types (Or‐CT0, Or‐CT1 and Or‐CT2) of O. rufipogon, but only two alleles (orf79a and orf79b) were observed in Or‐CT0 type of O. sativa, while no orf79 allele was found in other types of O. sativa. Our results also revealed that the orf79 alleles in cultivated rice originated from the wild rice population in South and South‐East Asia. In addition, strong positive selection pressure was detected on the sequence variations of orf79 alleles, and a special evolutionary strategy was noted in these gametophytic CMS‐related genes, suggesting that their divergence could be beneficial to their survival in evolution.

The plastid is an essential organelle in autotrophic plant cells, descending from free-living cyanobacteria and acquired by early eukaryotic cells through endosymbiosis roughly one billion years ago. It contained a streamlined genome (plastome) that is uniparentally inherited and non-recombinant, which makes it an ideal tool for resolving the origin and diversity of plant species and populations. In the present study, a large dataset was amassed by de novo assembling plastomes from 295 common wild rice (Oryza rufipogon Griff.) and 1135 Asian cultivated rice (Oryza sativa L.) accessions, supplemented with 34 plastomes from other Oryza species. From this dataset, the phylogenetic relationships and biogeographic history of O. rufipogon and O. sativa were reconstructed. Our results revealed two major maternal lineages across the two species, which further diverged into nine well supported genetic clusters. Among them, the Or-wj-I/II/III and Or-wi-I/II genetic clusters were shared with cultivated (percentage for each cluster ranging 54.9%∼99.3%) and wild rice accessions. Molecular dating, phylogeographic analyses and reconstruction of population historical dynamics indicated an earlier origin of the Or-wj-I/II genetic clusters from East Asian with at least two population expansions, and later origins of other genetic clusters from multiple regions with one or more population expansions. These results supported a single origin of japonica rice (mainly in Or-wj-I/II) and multiple origins of indica rice (in all five clusters) for the history of rice domestication. The massive plastomic data set presented here provides an important resource for understanding the history and evolution of rice domestication as well as a genomic resources for use in future breeding and conservation efforts.

Nitrogen metabolism (NM) plays an essential role in response to abiotic stresses for plants. Enzyme activities have been extensively studied for nitrogen metabolism-associated pathways, but the knowledge of nitrogen metabolism-associated genes involved in stress response is still limited, especially for rice. In this study, we performed the genome-wide characterization of the genes putatively involved in nitrogen metabolism. A total of 1110 potential genes were obtained to be involved in nitrogen metabolism from eight species (Arabidopsis thaliana (L.) Heynh., Glycine max (L.) Merr., Brassica napus L., Triticum aestivum L., Sorghum bicolor L., Zea mays L., Oryza sativa L. and Amborella trichopoda Baill.), especially 104 genes in rice. The comparative phylogenetic analysis of the superfamily revealed the complicated divergence of different NM genes. The expression analysis among different tissues in rice indicates the NM genes showed diverse functions in the pathway of nitrogen absorption and assimilation. Distinct expression patterns of NM genes were observed in rice under drought stress, heat stress, and salt stress, indicating that the NM genes play a curial role in response to abiotic stress. Most NM genes showed a down-regulated pattern under heat stress, while complicated expression patterns were observed for different genes under salt stress and drought stress. The function of four representative NM genes (OsGS2, OsGLU, OsGDH2, and OsAMT1;1) was further validated by using qRT-PCR analysis to confirm their responses to these abiotic stresses. Based on the predicted transcription factor binding sites (TFBSs), we built a co-expression regulatory network containing transcription factors (TFs) and NM genes, of which the constructed ERF and Dof genes may act as the core genes to respond to abiotic stresses. This study provides novel sights to the interaction between nitrogen metabolism and the response to abiotic stresses.

The genus Dalbergia contains more than 200 species, several of which are trees that produce traditional medicines and extremely high-value timber commonly referred to as rosewood. Due to the rarity of these species in the wild, the high value of the timber, and a growing international illicit trade, CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) has listed the entire genus in appendix II and the species Dalbergia nigra in appendix I because species in this genus are considered at risk of extinction. Given this, and the fact that species or even genus level determination is nearly impossible from cut timber morphology, alternative molecular methods are needed to identify and track intercepted rosewood. To better identify rosewood using molecular methods, we sequenced and assembled eight chloroplast genomes including D. nigra as well as conducted comparative analyses with all other available chloroplast genomes in Dalbergia and closely related lineages. From these analyses, numerous repeats including simple sequence repeats (SSR) and conserved nucleotide polymorphisms unique to subclades within the genus were detected. From phylogenetic analysis based on the CDS from 77 chloroplast genes, the groups Siam rosewood and scented rosewood resolved as monophyletic, supporting the morphological traits used to delimit these species. In addition, several instances of paraphyly and polyphyly resulting from mismatches between taxonomic determinations and phylogenetic tree topology were identified. Ultimately, the highly variable regions in the chloroplast genomes will provide useful plastid markers for further studies regarding the identification, phylogeny, and population genetics of Dalbergia species, including those frequently intercepted in illegal trade.

Background: Availability of related rice species is critical for rice breeding and improvement. Two distinct species of domesticated rice exist in the genus Oryza: Oryza sativa (Asian rice) and Oryza glaberrima (African rice). New rice for Africa (NERICA) is derived from interspecific crosses between these two species. Molecular profiling of these germplasms is important for both genetics and breeding studies. We used 30 polymorphic SSR markers to assess the genetic diversity and molecular fingerprints of 53 rice genotypes of O. sativa, O. glaberrima, and NERICA. Results: In total, 180 alleles were detected. Average polymorphism information content and Shannon's information index were 0.638 and 1.390, respectively. Population structure and neighbor-joining phylogenetic tree revealed that 53 genotypes grouped into three distinct subpopulations conforming to the original three groups, except three varieties (IR66417, WAB450-4, MZCD74), and that NERICA showed a smaller genetic distance from O. sativa genotypes (0.774) than from O. glaberrima genotypes (0.889). A molecular fingerprint map of the 53 accessions was constructed with a novel encoding method based on the SSR polymorphic alleles. Ten specific SSR markers displayed different allelic profiles between the O. glaberrima and O. sativa genotypes. Conclusions: Genetic diversity studies revealed that 50 rice types were clustered into different subpopulations whereas three genotypes were admixtures. Molecular fingerprinting and 10 specific markers were obtained to identify the 53 rice genotypes. These results can facilitate the potential utilization of sibling species in rice breeding and molecular classification of O. sativa and O. glaberrima germplasms. Keywords: African rice, Asian rice, Fingerprinting, Food security, Genetic relationship, Microsatellite markers, Molecular profiling, Phylogenetic tree, Polymorphic alleles, Rice breeding, SSR

The introduction of closely related species genomic fragments is an effective way to enrich genetic diversity and creates new germplasms in crops. Here, we studied the genetic diversity of an introgression line (IL) population composed of 106 ILs derived from an interspecific tetra cross between O. glaberrima and O. sativa (RAM3/Jin23B//Jin23B///YuetaiB). The proportion of O. glaberrima genome (PGG) in the ILs ranged from 0.3% to 36.7%, with an average value of 12.32% which is close to the theoretically expected proportion. A total of 250 polymorphic alleles were amplified by 21 AFLP primer combinations with an average of 12 alleles per primer. Population structure analysis revealed that the IL population can be divided into four genetically distinct subpopulations. Both principal component analysis and neighbor-joining tree analysis showed that ILs with a higher PGG displayed greater genetic diversity. Canonical discriminant analysis identified six phenotypic traits (plant height, yield per plant, filled grain percentage, panicle length, panicle number and days to flowering) as the main discriminatory traits among the ILs and between the subpopulations and showed significant phenotypic distances between subpopulations. The effects of PGG on phenotypic traits in the ILs were estimated using a linear admixed model, which showed a significant positive effect on grain yield per plant (0.286±0.117), plant height (0.418 ± 0.132), panicle length (0.663 ± 0.107), and spikelet number per panicle (0.339 ± 0.128), and a significant negative effect on filled grain percentage (-0.267 ± 0.123) and days to flowering (-0.324 ± 0.075). We found that an intermediate range (10% - 20%) of PGG was more effective for producing ILs with favorable integrated agronomic traits. Our results confirm that construction of IL population carrying O. glaberrima genomic fragments could be an effective approach to increase the genetic diversity of O. sativa genome and an appropriate level of PGG could facilitate pyramiding more favorable genes for developing more adaptive and productive rice.

In the present study, a set of 79 rice introgression lines (ILs) carrying variant introgressed segments of African rice (Oryza glaberrima Stued.) was used to identify quantitative trait loci (QTL) and heterotic loci (HL) associated with 7 agronomic traits. A total of 180 polymorphic markers between the donor and recurrent parents were found and 115 markers were used to identify the segregation of the introgression fragments. Based on the genotypic data of the ILs and test variety GZ63S as well as the phenotypic data of the IL and PIH, QTLs and HLs can be mapped on introgressed chromosome segments. One representative marker on each specific introgressed segment was defined as a QTL or a HL. 24 QTLs associated with six agronomic traits were mapped on 9 chromosomes and 23 interspecific HLs for seven agronomic traits were identified on 10 chromosomes in 2 years. Among them, 22 QTLs and 19 HLs were found to be associated with 5 yield-related traits respectively. The PIH (F1) testcross population showed superiority in most yield-related traits and was characterized by a high frequency of overdominant interspecific HLs. In addition, the pleiotropism was found in 5 marker loci for 11 QTLs associated with five agronomic traits and 4 marker loci for ten interspecific HLs for all the seven traits. This study is the first attempt for the identification of interspecific HLs between the two cultivated rice species, Asian rice (Oryza sativa L.) and African rice (O. glaberrima Steud.). Therefore, our results may help to lay the foundation for exploring the genetic mechanism of interspecific heterosis in rice. [ABSTRACT FROM AUTHOR]