Draft genome sequence, and a sequence-defined genetic linkage map of the legume crop species Lupinus angustifolius L

Pleistocene diversification of unifoliolate-leaved Lupinus (Leguminosae: Papilionoideae) in Florida

The importance and prevalence of recent ice-age and post-glacial speciation and species diversification during the Pleistocene across many organismal groups and physiographic settings are well established. However, the extent to which Pleistocene diversification can be attributed to climatic oscillations and their effects on distribution ranges and population structure remains debatable. In this study, we use morphologic, geographic and genetic (RADseq) data to document Pleistocene speciation and intra-specific diversification of the unifoliolate-leaved clade of Florida Lupinus, a small group of species largely restricted to inland and coastal sand ridges across the Florida peninsula and panhandle. Phylogenetic and demographic analyses alongside morphological and geographic evidence suggest that recent speciation and intra-specific divergence within this clade were driven by a combination of non-adaptive allopatric divergence caused by edaphic niche conservatism and opportunities presented by the emergence of new post-glacial sand ridge habitats. These results highlight the central importance of even modest geographic isolation and short periods of allopatric divergence following range expansion in the emergence of new taxa and add to the growing evidence that Pleistocene climatic oscillations may contribute to rapid diversification in a myriad of physiographic settings. Furthermore, our results shed new light on long-standing taxonomic debate surrounding the number of species in the Florida unifoliate Lupinus clade providing support for recognition of five species and a set of intra-specific variants. The important conservation implications for the narrowly restricted, highly endangered species Lupinus aridorum, which we show to be genetically distinct from its sister species Lupinus westianus, are discussed.

Advancing Grain Legumes Domestication and Evolution Studies with Genomics

Grain legumes were domesticated in parallel with cereals in several regions of the world and formed the economic basis of early farming cultures. Since then, legumes have played a vital role in human and animal diets and in fostering agrobiodiversity. Increasing grain legume cultivation will be crucial to safeguard nutritional security and the resilience of agricultural ecosystems across the globe. A better understanding of the molecular underpinnings of domestication and crop evolution of grain legumes may be translated into practical approaches in modern breeding programs to stabilize yield, which is threatened by evolving pathogens and changing climates. During recent decades, domestication research in all crops has greatly benefited from the fast progress in genomic technologies. Yet still, many questions surrounding the domestication and diversification of legumes remain unanswered. In this review, we assess the potential of genomic approaches in grain legume research. We describe the centers of origin and the crucial domestication traits of grain legumes. In addition, we survey the effect of domestication on both above-ground and below-ground traits that have economic importance. Finally, we discuss open questions in grain legume domestication and diversification and outline how to bridge the gap between the preservation of historic crop diversity and their utilization in modern plant breeding.

A pan-genome and chromosome-length reference genome of narrow-leafed lupin (Lupinus angustifolius) reveals genomic diversity and insights into key industry and biological traits

Narrow-leafed lupin (NLL; Lupinus angustifolius) is a key rotational crop for sustainable farming systems, whose grain is high in protein content. It is a gluten-free, non-genetically modified, alternative protein source to soybean (Glycine max) and as such has gained interest as a human food ingredient. Here, we present a chromosome-length reference genome for the species and a pan-genome assembly comprising 55 NLL lines, including Australian and European cultivars, breeding lines and wild accessions. We present the core and variable genes for the species and report on the absence of essential mycorrhizal associated genes. The genome and pan-genomes of NLL and its close relative white lupin (Lupinus albus) are compared. Furthermore, we provide additional evidence supporting LaRAP2-7 as the key alkaloid regulatory gene for NLL and demonstrate the NLL genome is underrepresented in classical NLR disease resistance genes compared to other sequenced legume species. The NLL genomic resources generated here coupled with previously generated RNA sequencing datasets provide new opportunities to fast-track lupin crop improvement.

Comparative transcriptome analysis of Lupinus polyphyllus Lindl. provides a rich molecular resource for research on coloration mechanism

Lupinus polyphyllus is rich in color, making it a well-known horticultural ornamental plant. However, little is known about the genes related to anthocyanin and carotenoid biosynthesis in L. polyphyllus. In this study, transcriptome sequencing was performed on eight different colors of L. polyphyllus. A total of 1.13 billion clean reads were obtained and assembled into 89,124 unigenes, which were then aligned with six databases, resulting in the identification of 54,823 annotated unigenes. Among these unigenes, 76 and 101 were involved in the biosynthetic pathway of carotenoids and anthocyanins, respectively. In addition, 505 transcription factors were revealed, which belonged to the MYB, R2R3-MYB, NAC, bHLH, and WD40 families. A total of 6,700 differentially expressed genes (DEGs) were obtained by comparative transcriptome analysis. Among them, 17 candidate unigenes (four carotenoid genes, seven anthocyanin genes, and six TFs) were specifically up-regulated for one or more colors of L. polyphyllus. Eight representative candidate unigenes were analyzed by qRT-PCR. The findings enrich the transcriptome database of lupine, and provide a rich molecular resource for research on the coloration mechanism of L. polyphyllus.

A successful defense of the narrow-leafed lupin against anthracnose involves quick and orchestrated reprogramming of oxidation-reduction, photosynthesis and pathogenesis-related genes

Narrow-leafed lupin (NLL, Lupinus angustifolius L.) is a legume plant cultivated for grain production and soil improvement. Worldwide expansion of NLL as a crop attracted various pathogenic fungi, including Colletotrichum lupini causing a devastating disease, anthracnose. Two alleles conferring improved resistance, Lanr1 and AnMan, were exploited in NLL breeding, however, underlying molecular mechanisms remained unknown. In this study, European NLL germplasm was screened with Lanr1 and AnMan markers. Inoculation tests in controlled environment confirmed effectiveness of both resistance donors. Representative resistant and susceptible lines were subjected to differential gene expression profiling. Resistance to anthracnose was associated with overrepresentation of "GO:0006952 defense response", "GO:0055114 oxidation-reduction process" and "GO:0015979 photosynthesis" gene ontology terms. Moreover, the Lanr1 (83A:476) line revealed massive transcriptomic reprogramming quickly after inoculation, whereas other lines showed such a response delayed by about 42 h. Defense response was associated with upregulation of TIR-NBS, CC-NBS-LRR and NBS-LRR genes, pathogenesis-related 10 proteins, lipid transfer proteins, glucan endo-1,3-beta-glucosidases, glycine-rich cell wall proteins and genes from reactive oxygen species pathway. Early response of 83A:476, including orchestrated downregulation of photosynthesis-related genes, coincided with the successful defense during fungus biotrophic growth phase, indicating effector-triggered immunity. Mandelup response was delayed and resembled general horizontal resistance.

Progress of Genomics-Driven Approaches for Sustaining Underutilized Legume Crops in the Post-Genomic Era

Legume crops, belonging to the Fabaceae family, are of immense importance for sustaining global food security. Many legumes are profitable crops for smallholder farmers due to their unique ability to fix atmospheric nitrogen and their intrinsic ability to thrive on marginal land with minimum inputs and low cultivation costs. Recent progress in genomics shows promise for future genetic gains in major grain legumes. Still it remains limited in minor legumes/underutilized legumes, including adzuki bean, cluster bean, horse gram, lathyrus, red clover, urd bean, and winged bean. In the last decade, unprecedented progress in completing genome assemblies of various legume crops and resequencing efforts of large germplasm collections has helped to identify the underlying gene(s) for various traits of breeding importance for enhancing genetic gain and contributing to developing climate-resilient cultivars. This review discusses the progress of genomic resource development, including genome-wide molecular markers, key breakthroughs in genome sequencing, genetic linkage maps, and trait mapping for facilitating yield improvement in underutilized legumes. We focus on 1) the progress in genomic-assisted breeding, 2) the role of whole-genome resequencing, pangenomes for underpinning the novel genomic variants underlying trait gene(s), 3) how adaptive traits of wild underutilized legumes could be harnessed to develop climate-resilient cultivars, 4) the progress and status of functional genomics resources, deciphering the underlying trait candidate genes with putative function in underutilized legumes 5) and prospects of novel breeding technologies, such as speed breeding, genomic selection, and genome editing. We conclude the review by discussing the scope for genomic resources developed in underutilized legumes to enhance their production and play a critical role in achieving the "zero hunger" sustainable development goal by 2030 set by the United Nations.

Biosynthesis of quinolizidine alkaloids in lupins: mechanistic considerations and prospects for pathway elucidation

Covering: up to 2022Quinolizidine alkaloids (QAs) are a class of alkaloids that accumulate in a variety of leguminous plants and have applications in the agricultural, pharmaceutical and chemical industries. QAs are notoriously present in cultivated lupins (Lupinus spp.) where they complicate the use of the valuable, high-protein beans due to their toxic properties and bitter taste. Compared to many other alkaloid classes, the biosynthesis of QAs is poorly understood, with only the two first pathway enzymes having been discovered so far. In this article, we review the different biosynthetic hypotheses that have been put forth in the literature (1988-2009) and highlight one particular hypothesis (1988) that agrees with the often ignored precursor feeding studies (1964-1994). Our focus is on the biosynthesis of the simple tetracyclic QA (-)-sparteine, from which many of the QAs found in lupins derive. We examine every pathway step on the way to (-)-sparteine and discuss plausible mechanisms, altogether proposing the involvement of 6-9 enzymes. Together with the new resources for gene discovery developed for lupins in the past few years, this review will contribute to the full elucidation of the QA pathway, including the identification and characterization of the missing pathway enzymes.

Genome-wide SSR markers in bottle gourd: development, characterization, utilization in assessment of genetic diversity of National Genebank of India and synteny with other related cucurbits

Lagenaria siceraria (Molina) Standley is an important cultivated crop with its immense importance in pharmaceutical industry and as vegetable. Its seed, root, stem, leaves, flower, and fruit are used as an ointment for ailment of various diseases throughout Asia. Despite its worldwide importance, informative co-dominant microsatellite markers in the bottle gourd crop are very restricted, impeding genetic improvement, cultivar identification, and phylogenetic studies. Next-generation sequencing has revolutionized the approaches for discovery, assessment, and validation of molecular markers. We conducted a genome-wide analysis, for developing SSR markers by utilizing restriction site-associated DNA sequencing (RAD-Seq) data obtained from NCBI. By performing in silico mining of microsatellite repeat motifs, we developed 45,066 perfect SSR markers. Of which 207 markers were successfully validated and 120 (57.97%) polymorphic primer pairs were utilized for an in-depth genetic diversity and population structure analysis of 96 accessions from the National Genebank of India. Tetranucleotide repeats (∼34.3%) were the most prevalent followed by trinucleotide repeats (∼30.73%), further 21.03%, 9.6%, and 4.3% of di-, penta-, and hexa-nucleotide repeats in the bottle gourd genome, respectively. Synteny of SSR markers on 11 bottle gourd linkage groups was correlated with the 7 chromosomes of cucumber (93.2%), 12 chromosomes of melon (87.4%), and 11 of watermelon (90.8%). The generated SSR markers provide a valuable tool for germplasm characterization, genetic linkage map construction, studying synteny, gene discovery, and for breeding in bottle gourd and other cucurbits species. KEY MESSAGE: Development of 45,066 perfect microsatellite markers as a valuable tool for marker assisted selection (MAS) in plant breeding.

The Diesel Tree Sindora glabra Genome Provides Insights Into the Evolution of Oleoresin Biosynthesis

Sindora glabra is an economically important tree that produces abundant oleoresin in the trunk. Here, we present a high-quality chromosome-scale assembly of S. glabra genome by combining Illumina HiSeq, Pacific Biosciences sequencing, and Hi-C technologies. The size of S. glabra genome was 1.11 Gb, with a contig N50 of 1.27 Mb and 31,944 predicted genes. This is the first sequenced genome of the subfamily Caesalpinioideae. As a sister taxon to Papilionoideae, S. glabra underwent an ancient genome triplication shared by core eudicots and further whole-genome duplication shared by early-legume in the last 73.3 million years. S. glabra harbors specific genes and expanded genes largely involved in stress responses and biosynthesis of secondary metabolites. Moreover, 59 terpene backbone biosynthesis genes and 64 terpene synthase genes were identified, which together with co-expressed transcription factors could contribute to the diversity and specificity of terpene compounds and high terpene content in S. glabra stem. In addition, 63 disease resistance NBS-LRR genes were found to be unique in S. glabra genome and their expression levels were correlated with the accumulation of terpene profiles, suggesting potential defense function of terpenes in S. glabra. These together provide new resources for understanding genome evolution and oleoresin production.

Identification of Gray Leaf Spot Disease Candidate Gene in Narrow-Leafed Lupin (Lupinus angustifolius L.)

Selection for resistance against gray leaf spot (GLS) is a major objective in the lupin breeding programs. A segregation ratio of 1:1 (resistant:susceptible) in F8 recombinant inbred lines (RIL8) derived from a cross between a breeding line 83A:476 (resistant to GLS) and a wild accession P27255 (susceptible to GLS) indicated that GLS was controlled by a single major gene. To develop molecular markers linked to GLS, in the beginning, only 11 resistant lines and six susceptible lines from the 83A:476 and P27255 population were genotyped with MFLP markers, and three MFLP markers were identified to be co-segregated with GLS. This method was very efficient, but the markers were located outside of the gene, and could not be used in other germplasms. Then QTL analysis and fine mapping were conducted to identify the gene. Finally, the gene was narrowed down to a 241-kb region containing two disease resistance genes. To further identify the candidate gene, DNA variants between accessions Tanjil (resistant to GLS) and Unicrop (susceptible to GLS) were analyzed. The results indicated that only one SNP was detected in the 241 kb region. This SNP was located in the TMV resistance protein N-like gene region and also identified between 83A:476 and P27255. Genotyping the Tanjil/Unicrop RIL8 population showed that this SNP co-segregated with GLS resistance. The phylogenetic tree analysis of this gene among 18 lupin accessions indicates that Australian resistant breeding line/varieties were clustered into one group and carry two resistant alleles, while susceptible accessions were clustered into different groups.

Alkaloids of narrow-leaved lupine as a factor determining alternative ways of the crop's utilization and breeding

Narrow-leaved lupine (Lupinus angustifolius L.), a valuable leguminous crop adapted to a wide range of climatic conditions, has a very short history of domestication. For many centuries it was used mainly as a green manure, since the success and prospects of the multi-purpose use of the species depend on its breeding improvement, in particular, on a particular concentration of alkaloids in seeds and green mass. The first varieties of scientific breeding were created only in the 1930s after the appearance of low-alkaloid mutants. Despite wide prospects for use in various areas of the national economy, unstable productivity and susceptibility to diseases hinder the production of this crop. Obviously, breeders deal only with a small part of the gene pool of the species and limited genetic resources, using mainly low-alkaloid (sweet) genotypes to create new varieties. The genetic potential of the species can be used more efficiently. At the same time, it is rational to create highly alkaloid (bitter) varieties for green manure, while food and feed varieties should not lose their adaptive potential, in particular, resistance to pathogens, due to the elimination of alkaloids. In this regard, it seems to be a productive idea to create ‘bitter/sweet’ varieties combining a high content of alkaloids in the vegetative organs and low in seeds, which can be achieved by regulating the synthesis/transport of alkaloids in the plant. The paper discusses the current state of use of the species as a green manure, fodder, food plant. Information is given on the quantity and qualitative composition of narrow-leaved lupine alkaloids, their applied value, in particular, fungicidal, antibacterial, insecticidal, the use of lupine alkaloids as active principles of drugs. Along with promising breeding considerations, the possibility of using technologies for processing raw high-alkaloid materials with the accompanying extraction of valuable ingredients for pharmaceuticals is discussed. Information is briefly presented about the genomic resources of the species and the prospects for their use in marker-assistant selection and genome editing.

Whole-genome assembly and resequencing reveal genomic imprint and key genes of rapid domestication in narrow-leafed lupin

Shifting from a livestock-based protein diet to a plant-based protein diet has been proposed as an essential requirement to maintain global food sustainability, which requires the increased production of protein-rich crops for direct human consumption. Meanwhile, the lack of sufficient genetic diversity in crop varieties is an increasing concern for sustainable food supplies. Countering this concern requires a clear understanding of the domestication process and dynamics. Narrow-leafed lupin (Lupinus angustifolius L.) has experienced rapid domestication and has become a new legume crop over the past century, with the potential to provide protein-rich seeds. Here, using long-read whole-genome sequencing, we assembled the third-generation reference genome for the narrow-leafed lupin cultivar Tanjil, comprising 20 chromosomes with a total genome size of 615.8 Mb and contig N50 = 5.65 Mb. We characterized the original mutation and putative biological pathway resulting in low seed alkaloid level that initiated the recent domestication of narrow-leafed lupin. We identified a 1133-bp insertion in the cis-regulatory region of a putative gene that may be associated with reduced pod shattering (lentus). A comparative analysis of genomic diversity in cultivars and wild types identified an apparent domestication bottleneck, as precisely predicted by the original model of the bottleneck effect on genetic variability in populations. Our results identify the key domestication genetic loci and provide direct genomic evidence for a domestication bottleneck, and open up the possibility of knowledge-driven de novo domestication of wild plants as an avenue to broaden crop plant diversity to enhance food security and sustainable low-carbon emission agriculture.

The Resistance of Narrow-Leafed Lupin to Diaporthe toxica Is Based on the Rapid Activation of Defense Response Genes

Narrow-leafed lupin (Lupinus angustifolius L.) is a grain legume crop that is advantageous in animal nutrition due to its high protein content; however, livestock grazing on stubble may develop a lupinosis disease that is related to toxins produced by a pathogenic fungus, Diaporthe toxica. Two major unlinked alleles, Phr1 and PhtjR, confer L. angustifolius resistance to this fungus. Besides the introduction of these alleles into modern cultivars, the molecular mechanisms underlying resistance remained unsolved. In this study, resistant and susceptible lines were subjected to differential gene expression profiling in response to D. toxica inoculation, spanning the progress of the infection from the early to latent phases. High-throughput sequencing of stem transcriptome and PCR quantification of selected genes were performed. Gene Ontology term analysis revealed that an early (24 h) response in the resistant germplasm encompassed activation of genes controlling reactive oxygen species and oxylipin biosynthesis, whereas in the susceptible germplasm, it comprised induction of xyloglucan endotransglucosylases/hydrolases. During the first five days of the infection, the number of genes with significantly altered expressions was about 2.6 times higher in resistant lines than in the susceptible line. Global transcriptome reprogramming involving the activation of defense response genes occurred in lines conferring Phr1 and PhtjR resistance alleles about 4–8 days earlier than in the susceptible germplasm.

Genetic and comparative mapping of Lupinus luteus L. highlight syntenic regions with major orthologous genes controlling anthracnose resistance and flowering time

Anthracnose susceptibility and ill-adapted flowering time severely affect Lupinus luteus yield, which has high seed protein content, is excellent for sustainable agriculture, but requires genetic improvement to fulfil its potential. This study aimed to (1) develop a genetic map; (2) define collinearity and regions of synteny with Lupinus angustifolius; and (3) map QTLs/candidate genes for anthracnose resistant and flowering time. A few linkage groups/genomic regions tended to be associated with segregation distortion, but did not affect the map. The developed map showed collinearity, and syntenic regions with L. angustifolius. Major QTLs were mapped in syntenic regions. Alleles from the wild parent and cultivar, explained 75% of the phenotypic variance for anthracnose resistance and 83% for early flowering, respectively. Marker sequences flanking the QTLs showed high homology with the Lanr1 gene and Flowering-locus-T of L. angustifolius. This suggests orthologous genes for both traits in the L. luteus genome. The findings are remarkable, revealing the potential to combine early flowering/anthracnose resistant in fulfilling yield capacity in L. luteus, and can be a major strategy in the genetic improvement and usage of this species for sustainable protein production. Allele sequences and PCR-marker tagging of these genes are being applied in marker assisted selection.

Innovative transcriptome-based genotyping highlights environmentally responsive genes for phenology, growth and yield in a non-model grain legume

The narrow-leafed lupin, Lupinus angustifolius L., is a grain legume crop, cultivated both as a green manure and as a source of protein for animal feed and human food production. During its domestication process, numerous agronomic traits were improved, however, only two trait-related genes were identified hitherto, both by linkage mapping. Genome-wide association studies (GWAS), exploiting genomic sequencing, did not select any novel candidate gene. In the present study, an innovative method of 3'-end reduced representation transcriptomic profiling, a massive analysis of cDNA ends, has been used for genotyping of 126 L. angustifolius lines surveyed by field phenotyping. Significant genotype × environment interactions were identified for all phenology and yield traits analysed. Principal component analysis of population structure evidenced European domestication bottlenecks, visualized by clustering of breeding materials and cultivars. GWAS provided contribution towards deciphering vernalization pathway in legumes, and, apart from highlighting known domestication loci (Ku/Julius and mol), designated novel candidate genes for L. angustifolius traits. Early phenology was associated with genes from vernalization, cold-responsiveness and phosphatidylinositol signalling pathways whereas high yield with genes controlling photosynthesis performance and abiotic stress (drought or heat) tolerance. PCR-based toolbox was developed and validated to enable tracking desired alleles in marker-assisted selection. Narrow-leafed lupin was genotyped with an innovative method of transcriptome profiling and phenotyped for phenology, growth and yield traits in field. Early phenology was found associated with genes from cold-response, vernalization and phosphatidylinositol signalling pathways, whereas high yield with genes running photosystem II and drought or heat stress response. Key loci were supplied with PCR-based toolbox for marker-assisted selection.

Development of PCR-based markers and whole-genome selection model for anthracnose resistance in white lupin (Lupinus albus L.)

White lupin (Lupinus albus L.) is a high-protein grain legume crop, grown since ancient Greece and Rome. Despite long domestication history, its cultivation remains limited, partly because of susceptibility to anthracnose. Only some late-flowering, bitter, low-yielding landraces from Ethiopian mountains displayed resistance to this devastating disease. The resistance is controlled by various genes, thereby complicating the breeding efforts. The objective of this study was developing tools for molecular tracking of Ethiopian resistance genes based on genotyping-by-sequencing (GBS) data, envisaging linkage mapping and genomic selection approaches. Twenty GBS markers from two major quantitative trait loci (QTLs), antr04_1/antr05_1 and antr04_2/antr05_2, were converted to PCR-based markers using assigned transcriptome sequences. Newly developed markers improved mapping resolution around both anthracnose resistance loci, providing more precise QTL estimation. PCR-based screening of diversified domesticated and primitive germplasm revealed the high specificity of two markers for the antr04_1/antr05_1 locus (TP222136 and TP47110) and one for the antr04_2/antr05_2 locus (TP338761), highlighted by simple matching coefficients of 0.96 and 0.89, respectively. Moreover, a genomic selection approach based on GBS data of a recombinant inbred line mapping population was assessed, providing an average predictive ability of 0.56. These tools can be used for preselection of candidate white lupin germplasm for anthracnose resistance assays.

Genetic diversity analysis for narrow-leafed lupin (Lupinus angustifolius L.) by SSR markers

Narrow-leafed lupin (Lupinus angustifolius L.) is used as grain legumes, fodder for livestock and green manure in the world and has a great potential to be developed as a new crop in China. In this study, we assessed the genetic diversity among a set of 109 newly introduced accessions of narrow-leafed lupin using 76 genomic SSR markers. Data analysis suggested that the average gene diversity index and average polymorphism information content (PIC) were 0.4758 and 0.4328, respectively. The mean allele number per loci (Na) was 6.3816. The population structure analysis identified two subgroups based on delta K (ΔK) values. This result is in accordance with that of a PCA. The AMOVA analysis showed that most of molecular variance were within population. These results will be useful to guide the genetic improvement of the narrow-leafed lupin crop in China.

A Tale of Two Families: Whole Genome and Segmental Duplications Underlie Glutamine Synthetase and Phosphoenolpyruvate Carboxylase Diversity in Narrow-Leafed Lupin (Lupinus angustifolius L.)

Narrow-leafed lupin (Lupinus angustifolius L.) has recently been supplied with advanced genomic resources and, as such, has become a well-known model for molecular evolutionary studies within the legume family—a group of plants able to fix nitrogen from the atmosphere. The phylogenetic position of lupins in Papilionoideae and their evolutionary distance to other higher plants facilitates the use of this model species to improve our knowledge on genes involved in nitrogen assimilation and primary metabolism, providing novel contributions to our understanding of the evolutionary history of legumes. In this study, we present a complex characterization of two narrow-leafed lupin gene families—glutamine synthetase (GS) and phosphoenolpyruvate carboxylase (PEPC). We combine a comparative analysis of gene structures and a synteny-based approach with phylogenetic reconstruction and reconciliation of the gene family and species history in order to examine events underlying the extant diversity of both families. Employing the available evidence, we show the impact of duplications on the initial complement of the analyzed gene families within the genistoid clade and posit that the function of duplicates has been largely retained. In terms of a broader perspective, our results concerning GS and PEPC gene families corroborate earlier findings pointing to key whole genome duplication/triplication event(s) affecting the genistoid lineage.

Candidate Domestication-Related Genes Revealed by Expression Quantitative Trait Loci Mapping of Narrow-Leafed Lupin (Lupinus angustifolius L.)

The last century has witnessed rapid domestication of the narrow-leafed lupin (Lupinus angustifolius L.) as a grain legume crop, exploiting discovered alleles conferring low-alkaloid content (iucundus), vernalization independence (Ku and Julius), and reduced pod shattering (lentus and tardus). In this study, a L. angustifolius mapping population was subjected to massive analysis of cDNA ends (MACE). The MACE yielded 4185 single nucleotide polymorphism (SNP) markers for linkage map improvement and 30,595 transcriptomic profiles for expression quantitative trait loci (eQTL) mapping. The eQTL highlighted a high number of cis- and trans-regulated alkaloid biosynthesis genes with gene expression orchestrated by a regulatory agent localized at iucundus locus, supporting the concept that ETHYLENE RESPONSIVE TRANSCRIPTION FACTOR RAP2-7 may control low-alkaloid phenotype. The analysis of Ku shed light on the vernalization response via FLOWERING LOCUS T and FD regulon in L. angustifolius, providing transcriptomic evidence for the contribution of several genes acting in C-repeat binding factor (CBF) cold responsiveness and in UDP-glycosyltransferases pathways. Research on lentus selected a DUF1218 domain protein as a candidate gene controlling the orientation of the sclerified endocarp and a homolog of DETOXIFICATION14 for purplish hue of young pods. An ABCG transporter was identified as a hypothetical contributor to sclerenchyma fortification underlying tardus phenotype.

Validation of Diaporthe toxica resistance markers in European Lupinus angustifolius germplasm and identification of novel resistance donors for marker-assisted selection

The fungus, Diaporthe toxica, anamorph Phomopsis sp., previously classified as P. leptostromiformis, is a plant endophyte and occasional pathogen, causing Phomopsis stem blight. This disease is damaging not only to lupins but also to the animals grazing on infected plants, due to the toxic secondary metabolites called phomopsins. The aim of this work was to validate markers for resistance to Phomopsis stem blight in narrow-leafed lupins and identify novel germplasm with increased levels of resistance to the disease. Plant inoculations were performed using ten isolates of D. toxica, originating from Australia and Poland. The European core collection of L. angustifolius was evaluated both in a controlled environment and with field experiments to classify the accessions based on their resistance to the disease. Simultaneously, the accessions were assayed with disease resistance markers to identify donors of hypothetical resistance alleles. We have found that the European lupin germplasm collection preserves wild and domesticated donors of at least two resistance genes to Phomopsis stem blight, including Phr1 and PhtjR. Molecular markers PhtjM7, InDel2, and InDel10, tagging PhtjR gene, were applicable for marker-assisted selection targeting the European gene pool with an expected accuracy of 95%. None of diagnostic markers for the Phr1 locus was found useful for European breeding programs; two existing markers Ph258M1 and Ph258M2 were unreliable, due to a high percentage of false-positive results (up to 58%) and a high recombination rate between markers (~ 30%).

Development of gene-based molecular markers tagging low alkaloid pauper locus in white lupin (Lupinus albus L.)

White lupin (Lupinus albus L.) is a legume grain crop cultivated since ancient Greece and Egypt. Modern white lupin cultivars are appreciated as a source of protein with positive nutraceutical impact. However, white lupins produce anti-nutritional compounds, quinolizidine alkaloids, which provide bitter taste and have a negative influence on human health. During domestication of this species, several recessive alleles at unlinked loci controlling low alkaloid content were selected. One of these loci, pauper, was exploited worldwide providing numerous low-alkaloid cultivars. However, molecular tracking of pauper has been hampered due to the lack of diagnostic markers. In the present study, the synteny-based approach was harnessed to target pauper locus. Single-nucleotide polymorphisms flanking pauper locus on white lupin linkage map as well as candidate gene sequences elucidated from the narrow-leafed lupin (L. angustifolius L.) chromosome segment syntenic to the pauper linkage group region were transformed to PCR-based molecular markers. These markers were analyzed both in the mapping population and world germplasm collection. From fourteen markers screened, eleven were localized at a distance below 1.5 cM from this locus, including five co-segregating with pauper. The linkage of these markers was confirmed by high LOD values (up to 58.4). Validation performed in the set of 127 bitter and 23 sweet accessions evidenced high applicability of one marker, LAGI01_35805_F1_R1, for pauper locus selection, highlighted by the low ratio of false-positive scores (2.5%). LAGI01_35805 represents a homolog of L. angustifolius acyltransferase-like (LaAT) gene which might hypothetically participate in the alkaloid biosynthesis process in lupins.

Impact of Chromosomal Rearrangements on the Interpretation of Lupin Karyotype Evolution

Plant genome evolution can be very complex and challenging to describe, even within a genus. Mechanisms that underlie genome variation are complex and can include whole-genome duplications, gene duplication and/or loss, and, importantly, multiple chromosomal rearrangements. Lupins (Lupinus) diverged from other legumes approximately 60 mya. In contrast to New World lupins, Old World lupins show high variability not only for chromosome numbers (2n = 32–52), but also for the basic chromosome number (x = 5–9, 13) and genome size. The evolutionary basis that underlies the karyotype evolution in lupins remains unknown, as it has so far been impossible to identify individual chromosomes. To shed light on chromosome changes and evolution, we used comparative chromosome mapping among 11 Old World lupins, with Lupinus angustifolius as the reference species. We applied set of L. angustifolius-derived bacterial artificial chromosome clones for fluorescence in situ hybridization. We demonstrate that chromosome variations in the species analyzed might have arisen from multiple changes in chromosome structure and number. We hypothesize about lupin karyotype evolution through polyploidy and subsequent aneuploidy. Additionally, we have established a cytogenomic map of L. angustifolius along with chromosome markers that can be used for related species to further improve comparative studies of crops and wild lupins.

The Use of Lupin as a Source of Protein in Animal Feeding: Genomic Tools and Breeding Approaches

Livestock production in the European Union EU is highly dependent on imported soybean, exposing the livestock farming system to risks related to the global trade of soybean. Lupin species could be a realistic sustainable alternative source of protein for animal feeding. Lupinus is a very diverse genus with many species. However, only four of them—namely, L. albus, L. angustifolius, L. luteus and L. mutabilis—are cultivated. Their use in livestock farming systems has many advantages in relation to economic and environmental impact. Generally, lupin grains are characterized by high protein content, while their oil content is relatively low but of high quality. On the other hand, the presence of quinolizidine alkaloids and their specific carbohydrate composition are the main antinutritional factors that prevent their use in animal feeding. This research is mainly related to L. albus and to L. angustifolius, and to a lesser extent, to L. lauteus and L. mutabilis. The breeding efforts are mostly focused on yield stabilization, resistance to biotic and abiotic stresses, biochemical structure associated with seed quality and late maturing. Progress is made in improving lupin with respect to the seed quality, as well as the tolerance to biotic and abiotic stress. It has to be noted that modern cultivars, mostly of L. albus and L. angustifolius, contain low levels of alkaloids. However, for future breeding efforts, the implementation of marker-assisted selection and the available genomic tools is of great importance.

Identification and profiling of narrow-leafed lupin (Lupinus angustifolius) microRNAs during seed development

BACKGROUND

Whilst information regarding small RNAs within agricultural crops is increasing, the miRNA composition of the nutritionally valuable pulse narrow-leafed lupin (Lupinus angustifolius) remains unknown.

RESULTS

By conducting a genome- and transcriptome-wide survey we identified 7 Dicer-like and 16 Argonaute narrow-leafed lupin genes, which were highly homologous to their legume counterparts. We identified 43 conserved miRNAs belonging to 16 families, and 13 novel narrow-leafed lupin-specific miRNAs using high-throughput sequencing of small RNAs from foliar and root and five seed development stages. We observed up-regulation of members of the miRNA families miR167, miR399, miR156, miR319 and miR164 in narrow-leafed lupin seeds, and confirmed expression of miR156, miR166, miR164, miR1507 and miR396 using quantitative RT-PCR during five narrow-leafed lupin seed development stages. We identified potential targets for the conserved and novel miRNAs and were able to validate targets of miR399 and miR159 using 5' RLM-RACE. The conserved miRNAs are predicted to predominately target transcription factors and 93% of the conserved miRNAs originate from intergenic regions. In contrast, only 43% of the novel miRNAs originate from intergenic regions and their predicted targets were more functionally diverse.

CONCLUSION

This study provides important insights into the miRNA gene regulatory networks during narrow-leafed lupin seed development.

Legume Cytosolic and Plastid Acetyl-Coenzyme-A Carboxylase Genes Differ by Evolutionary Patterns and Selection Pressure Schemes Acting before and after Whole-Genome Duplications

Acetyl-coenzyme A carboxylase (ACCase, E.C.6.4.1.2) catalyzes acetyl-coenzyme A carboxylation to malonyl coenzyme A. Plants possess two distinct ACCases differing by cellular compartment and function. Plastid ACCase contributes to de novo fatty acid synthesis, whereas cytosolic enzyme to the synthesis of very long chain fatty acids, phytoalexins, flavonoids, and anthocyanins. The narrow leafed lupin (Lupinus angustifolius L.) represents legumes, a plant family which evolved by whole-genome duplications (WGDs). The study aimed on the contribution of these WGDs to the multiplication of ACCase genes and their further evolutionary patterns. The molecular approach involved bacterial artificial chromosome (BAC) library screening, fluorescent in situ hybridization, linkage mapping, and BAC sequencing. In silico analysis encompassed sequence annotation, comparative mapping, selection pressure calculation, phylogenetic inference, and gene expression profiling. Among sequenced legumes, the highest number of ACCase genes was identified in lupin and soybean. The most abundant plastid ACCase subunit genes were accB. ACCase genes in legumes evolved by WGDs, evidenced by shared synteny and Bayesian phylogenetic inference. Transcriptional activity of almost all copies was confirmed. Gene duplicates were conserved by strong purifying selection, however, positive selection occurred in Arachis (accB2) and Lupinus (accC) lineages, putatively predating the WGD event(s). Early duplicated accA and accB genes underwent transcriptional sub-functionalization.

Construction of an ultra-high density consensus genetic map, and enhancement of the physical map from genome sequencing in Lupinus angustifolius

An ultra-high density genetic map containing 34,574 sequence-defined markers was developed in Lupinus angustifolius. Markers closely linked to nine genes of agronomic traits were identified. A physical map was improved to cover 560.5 Mb genome sequence. Lupin (Lupinus angustifolius L.) is a recently domesticated legume grain crop. In this study, we applied the restriction-site associated DNA sequencing (RADseq) method to genotype an F₉ recombinant inbred line population derived from a wild type × domesticated cultivar (W × D) cross. A high density linkage map was developed based on the W × D population. By integrating sequence-defined DNA markers reported in previous mapping studies, we established an ultra-high density consensus genetic map, which contains 34,574 markers consisting of 3508 loci covering 2399 cM on 20 linkage groups. The largest gap in the entire consensus map was 4.73 cM. The high density W × D map and the consensus map were used to develop an improved physical map, which covered 560.5 Mb of genome sequence data. The ultra-high density consensus linkage map, the improved physical map and the markers linked to genes of breeding interest reported in this study provide a common tool for genome sequence assembly, structural genomics, comparative genomics, functional genomics, QTL mapping, and molecular plant breeding in lupin.

Transcript profiling of a bitter variety of narrow-leafed lupin to discover alkaloid biosynthetic genes

Lupins (Lupinus spp.) are nitrogen-fixing legumes that accumulate toxic alkaloids in their protein-rich beans. These anti-nutritional compounds belong to the family of quinolizidine alkaloids (QAs), which are of interest to the pharmaceutical and chemical industries. To unleash the potential of lupins as protein crops and as sources of QAs, a thorough understanding of the QA pathway is needed. However, only the first enzyme in the pathway, lysine decarboxylase (LDC), is known. Here, we report the transcriptome of a high-QA variety of narrow-leafed lupin (L. angustifolius), obtained using eight different tissues and two different sequencing technologies. In addition, we present a list of 33 genes that are closely co-expressed with LDC and that represent strong candidates for involvement in lupin alkaloid biosynthesis. One of these genes encodes a copper amine oxidase able to convert the product of LDC, cadaverine, into 1-piperideine, as shown by heterologous expression and enzyme assays. Kinetic analysis revealed a low KM value for cadaverine, supporting a role as the second enzyme in the QA pathway. Our transcriptomic data set represents a crucial step towards the discovery of enzymes, transporters, and regulators involved in lupin alkaloid biosynthesis.

A high-density consensus linkage map of white lupin highlights synteny with narrow-leafed lupin and provides markers tagging key agronomic traits

White lupin (Lupinus albus L.) is a valuable source of seed protein, carbohydrates and oil, but requires genetic improvement to attain its agronomic potential. This study aimed to (i) develop a new high-density consensus linkage map based on new, transcriptome-anchored markers; (ii) map four important agronomic traits, namely, vernalization requirement, seed alkaloid content, and resistance to anthracnose and Phomopsis stem blight; and, (iii) define regions of synteny between the L. albus and narrow-leafed lupin (L. angustifolius L.) genomes. Mapping of white lupin quantitative trait loci (QTLs) revealed polygenic control of vernalization responsiveness and anthracnose resistance, as well as a single locus regulating seed alkaloid content. We found high sequence collinearity between white and narrow-leafed lupin genomes. Interestingly, the white lupin QTLs did not correspond to previously mapped narrow-leafed lupin loci conferring vernalization independence, anthracnose resistance, low alkaloids and Phomopsis stem blight resistance, highlighting different genetic control of these traits. Our suite of allele-sequenced and PCR validated markers tagging these QTLs is immediately applicable for marker-assisted selection in white lupin breeding. The consensus map constitutes a platform for synteny-based gene cloning approaches and can support the forthcoming white lupin genome sequencing efforts.

Legume isoflavone synthase genes have evolved by whole-genome and local duplications yielding transcriptionally active paralogs

Isoflavone synthase (IFS) is the key enzyme of isoflavonoid biosynthesis. IFS genes were identified in numerous species, although their evolutionary patterns have not yet been reconstructed. To address this issue, we performed structural and functional genomic analysis. Narrow leafed lupin, Lupinus angustifolius L., was used as a reference species for the genus, because it has the most developed molecular tools available. Nuclear genome BAC library clones carrying IFS homologs were localized by linkage mapping and fluorescence in situ hybridization in three chromosome pairs. Annotation of BAC, scaffold and transcriptome sequences confirmed the presence of three full-length IFS genes in the genome. Microsynteny analysis and Bayesian inference provided clear evidence that IFS genes in legumes have evolved by lineage-specific whole-genome and tandem duplications. Gene expression profiling and RNA-seq data mining showed that the vast majority of legume IFS copies have maintained their transcriptional activity. L. angustifolius IFS homologs exhibited organ-specific expression patterns similar to those observed in other Papilionoideae. Duplicated lupin IFS homologs retained non-negligible levels of substitutions in conserved motifs, putatively due to positive selection acting during early evolution of the genus, before the whole-genome duplication. Strong purifying selection preserved newly arisen IFS duplicates from further nonsynonymous changes.

The evolutionary fate of the chloroplast and nuclear rps16 genes as revealed through the sequencing and comparative analyses of four novel legume chloroplast genomes from Lupinus

The Fabaceae family is considered as a model system for understanding chloroplast genome evolution due to the presence of extensive structural rearrangements, gene losses and localized hypermutable regions. Here, we provide sequences of four chloroplast genomes from the Lupinus genus, belonging to the underinvestigated Genistoid clade. Notably, we found in Lupinus species the functional loss of the essential rps16 gene, which was most likely replaced by the nuclear rps16 gene that encodes chloroplast and mitochondrion targeted RPS16 proteins. To study the evolutionary fate of the rps16 gene, we explored all available plant chloroplast, mitochondrial and nuclear genomes. Whereas no plant mitochondrial genomes carry an rps16 gene, many plants still have a functional nuclear and chloroplast rps16 gene. Ka/Ks ratios revealed that both chloroplast and nuclear rps16 copies were under purifying selection. However, due to the dual targeting of the nuclear rps16 gene product and the absence of a mitochondrial copy, the chloroplast gene may be lost. We also performed comparative analyses of lupine plastomes (SNPs, indels and repeat elements), identified the most variable regions and examined their phylogenetic utility. The markers identified here will help to reveal the evolutionary history of lupines, Genistoids and closely related clades.

Oil body biogenesis and biotechnology in legume seeds

The seeds of many legume species including soybean, Pongamia pinnata and the model legume Medicago truncatula store considerable oil, apart from protein, in their cotyledons. However, as a group, legume storage strategies are quite variable and provide opportunities for better understanding of carbon partitioning into different storage products. Legumes with their ability to fix nitrogen can also increase the sustainability of agricultural systems. This review integrates the cell biology, biochemistry and molecular biology of oil body biogenesis before considering biotechnology strategies to enhance oil body biosynthesis. Cellular aspects of packaging triacylglycerol (TAG) into oil bodies are emphasized. Enhancing seed oil content has successfully focused on the up-regulation of the TAG biosynthesis pathways using overexpression of enzymes such as diacylglycerol acyltransferase1 and transcription factors such as WRINKLE1 and LEAFY COTYLEDON1. While these strategies are central, decreasing carbon flow into other storage products and maximizing the packaging of oil bodies into the cytoplasm are other strategies that need further examination. Overall there is much potential for integrating carbon partitioning, up-regulation of fatty acid and TAG synthesis and oil body packaging, for enhancing oil levels. In addition to the potential for integrated strategies to improving oil yields, the capacity to modify fatty acid composition and use of oil bodies as platforms for the production of recombinant proteins in seed of transgenic legumes provide other opportunities for legume biotechnology.

De novo Transcriptome Profiling of Flowers, Flower Pedicels and Pods of Lupinus luteus (Yellow Lupine) Reveals Complex Expression Changes during Organ Abscission

Yellow lupine (Lupinus luteus L., Taper c.), a member of the legume family (Fabaceae L.), has an enormous practical importance. Its excessive flower and pod abscission represents an economic drawback, as proper flower and seed formation and development is crucial for the plant's productivity. Generative organ detachment takes place at the basis of the pedicels, within a specialized group of cells collectively known as the abscission zone (AZ). During plant growth these cells become competent to respond to specific signals that trigger separation and lead to the abolition of cell wall adhesion. Little is known about the molecular network controlling the yellow lupine organ abscission. The aim of our study was to establish the divergences and similarities in transcriptional networks in the pods, flowers and flower pedicels abscised or maintained on the plant, and to identify genes playing key roles in generative organ abscission in yellow lupine. Based on de novo transcriptome assembly, we identified 166,473 unigenes representing 219,514 assembled unique transcripts from flowers, flower pedicels and pods undergoing abscission and from control organs. Comparison of the cDNA libraries from dropped and control organs helped in identifying 1,343, 2,933 and 1,491 differentially expressed genes (DEGs) in the flowers, flower pedicels and pods, respectively. In DEG analyses, we focused on genes involved in phytohormonal regulation, cell wall functioning and metabolic pathways. Our results indicate that auxin, ethylene and gibberellins are some of the main factors engaged in generative organ abscission. Identified 28 DEGs common for all library comparisons are involved in cell wall functioning, protein metabolism, water homeostasis and stress response. Interestingly, among the common DEGs we also found an miR169 precursor, which is the first evidence of micro RNA engaged in abscission. A KEGG pathway enrichment analysis revealed that the identified DEGs were predominantly involved in carbohydrate and amino acid metabolism, but some other pathways were also targeted. This study represents the first comprehensive transcriptome-based characterization of organ abscission in L. luteus and provides a valuable data source not only for understanding the abscission signaling pathway in yellow lupine, but also for further research aimed at improving crop yields.

A comprehensive draft genome sequence for lupin (Lupinus angustifolius), an emerging health food: insights into plant-microbe interactions and legume evolution

Lupins are important grain legume crops that form a critical part of sustainable farming systems, reducing fertilizer use and providing disease breaks. It has a basal phylogenetic position relative to other crop and model legumes and a high speciation rate. Narrow-leafed lupin (NLL; Lupinus angustifolius L.) is gaining popularity as a health food, which is high in protein and dietary fibre but low in starch and gluten-free. We report the draft genome assembly (609 Mb) of NLL cultivar Tanjil, which has captured >98% of the gene content, sequences of additional lines and a dense genetic map. Lupins are unique among legumes and differ from most other land plants in that they do not form mycorrhizal associations. Remarkably, we find that NLL has lost all mycorrhiza-specific genes, but has retained genes commonly required for mycorrhization and nodulation. In addition, the genome also provided candidate genes for key disease resistance and domestication traits. We also find evidence of a whole-genome triplication at around 25 million years ago in the genistoid lineage leading to Lupinus. Our results will support detailed studies of legume evolution and accelerate lupin breeding programmes.

Evolution and structural diversification of Nictaba-like lectin genes in food crops with a focus on soybean (Glycine max)

Background and Aims

The Nictaba family groups all proteins that show homology to Nictaba, the tobacco lectin. So far, Nictaba and an Arabidopsis thaliana homologue have been shown to be implicated in the plant stress response. The availability of more than 50 sequenced plant genomes provided the opportunity for a genome-wide identification of Nictaba -like genes in 15 species, representing members of the Fabaceae, Poaceae, Solanaceae, Musaceae, Arecaceae, Malvaceae and Rubiaceae. Additionally, phylogenetic relationships between the different species were explored. Furthermore, this study included domain organization analysis, searching for orthologous genes in the legume family and transcript profiling of the Nictaba -like lectin genes in soybean.

Methods

Using a combination of BLASTp, InterPro analysis and hidden Markov models, the genomes of Medicago truncatula , Cicer arietinum , Lotus japonicus , Glycine max , Cajanus cajan , Phaseolus vulgaris , Theobroma cacao , Solanum lycopersicum , Solanum tuberosum , Coffea canephora , Oryza sativa , Zea mays, Sorghum bicolor , Musa acuminata and Elaeis guineensis were searched for Nictaba -like genes. Phylogenetic analysis was performed using RAxML and additional protein domains in the Nictaba-like sequences were identified using InterPro. Expression analysis of the soybean Nictaba -like genes was investigated using microarray data.

Key Results

Nictaba -like genes were identified in all studied species and analysis of the duplication events demonstrated that both tandem and segmental duplication contributed to the expansion of the Nictaba gene family in angiosperms. The single-domain Nictaba protein and the multi-domain F-box Nictaba architectures are ubiquitous among all analysed species and microarray analysis revealed differential expression patterns for all soybean Nictaba-like genes.

Conclusions

Taken together, the comparative genomics data contributes to our understanding of the Nictaba -like gene family in species for which the occurrence of Nictaba domains had not yet been investigated. Given the ubiquitous nature of these genes, they have probably acquired new functions over time and are expected to take on various roles in plant development and defence.

Potential Uses of Wild Germplasms of Grain Legumes for Crop Improvement

Challenged by population increase, climatic change, and soil deterioration, crop improvement is always a priority in securing food supplies. Although the production of grain legumes is in general lower than that of cereals, the nutritional value of grain legumes make them important components of food security. Nevertheless, limited by severe genetic bottlenecks during domestication and human selection, grain legumes, like other crops, have suffered from a loss of genetic diversity which is essential for providing genetic materials for crop improvement programs. Illustrated by whole-genome-sequencing, wild relatives of crops adapted to various environments were shown to maintain high genetic diversity. In this review, we focused on nine important grain legumes (soybean, peanut, pea, chickpea, common bean, lentil, cowpea, lupin, and pigeonpea) to discuss the potential uses of their wild relatives as genetic resources for crop breeding and improvement, and summarized the various genetic/genomic approaches adopted for these purposes.

ERAMOSA controls lateral branching in snapdragon

Plant forms display a wide variety of architectures, depending on the number of lateral branches, internode elongation and phyllotaxy. These are in turn determined by the number, the position and the fate of the Axillary Meristems (AMs). Mutants that affect AM determination during the vegetative phase have been isolated in several model plants. Among these genes, the GRAS transcription factor LATERAL SUPPRESSOR (Ls) plays a pivotal role in AM determination during the vegetative phase. Hereby we characterize the phylogenetic orthologue of Ls in Antirrhinum, ERAMOSA (ERA). Our data supported ERA control of AM formation during both the vegetative and the reproductive phase in snapdragon. A phylogenetic analysis combined with an analysis of the synteny of Ls in several species strongly supported the hypothesis that ERA is a phylogenetic orthologue of Ls, although it plays a broader role. During the reproductive phase ERA promotes the establishment of the stem niche at the bract axis but, after the reproductive transition, it is antagonized by the MADS box transcription factor SQUAMOSA (SQUA). Surprisingly double mutant era squa plants display a squa phenotype developing axillary meristems, which can eventually turn into inflorescences or flowers.

Quinolizidine Alkaloid Biosynthesis in Lupins and Prospects for Grain Quality Improvement

Quinolizidine alkaloids (QAs) are toxic secondary metabolites found within the genus Lupinus, some species of which are commercially important grain legume crops including Lupinus angustifolius (narrow-leafed lupin, NLL), L. luteus (yellow lupin), L. albus (white lupin), and L. mutabilis (pearl lupin), with NLL grain being the most largely produced of the four species in Australia and worldwide. While QAs offer the plants protection against insect pests, the accumulation of QAs in lupin grain complicates its use for food purposes as QA levels must remain below the industry threshold (0.02%), which is often exceeded. It is not well understood what factors cause grain QA levels to exceed this threshold. Much of the early work on QA biosynthesis began in the 1970-1980s, with many QA chemical structures well-characterized and lupin cell cultures and enzyme assays employed to identify some biosynthetic enzymes and pathway intermediates. More recently, two genes associated with these enzymes have been characterized, however, the QA biosynthetic pathway remains only partially elucidated. Here, we review the research accomplished thus far concerning QAs in lupin and consider some possibilities for further elucidation and manipulation of the QA pathway in lupin crops, drawing on examples from model alkaloid species. One breeding strategy for lupin is to produce plants with high QAs in vegetative tissues while low in the grain in order to confer insect resistance to plants while keeping grain QA levels within industry regulations. With the knowledge achieved on alkaloid biosynthesis in other plant species in recent years, and the recent development of genomic and transcriptomic resources for NLL, there is considerable scope to facilitate advances in our knowledge of QAs, leading to the production of improved lupin crops.

The loss of vernalization requirement in narrow-leafed lupin is associated with a deletion in the promoter and de-repressed expression of a Flowering Locus T (FT) homologue

Adaptation of Lupinus angustifolius (narrow-leafed lupin) to cropping in southern Australian and northern Europe was transformed by a dominant mutation (Ku) that removed vernalization requirement for flowering. The Ku mutation is now widely used in lupin breeding to confer early flowering and maturity. We report here the identity of the Ku mutation. We used a range of genetic, genomic and gene expression approaches to determine whether Flowering Locus T (FT) homologues are associated with the Ku locus. One of four FT homologues present in the narrow-leafed lupin genome, LanFTc1, perfectly co-segregated with the Ku locus in a reference mapping population. Expression of LanFTc1 in the ku (late-flowering) parent was strongly induced by vernalization, in contrast to the Ku (early-flowering) parent, which showed constitutively high LanFTc1 expression. Co-segregation of this expression phenotype with the LanFTc1 genotype indicated that the Ku mutation impairs cis-regulation of LanFTc1. Sequencing of LanFTc1 revealed a 1.4-kb deletion in the promoter region, which was perfectly predictive of vernalization response in 216 wild and domesticated accessions. Linkage disequilibrium rapidly decayed around LanFTc1, suggesting that this deletion caused the loss of vernalization response. This is the first time a legume FTc subclade gene has been implicated in the vernalization response.

Expansion of the phosphatidylethanolamine binding protein family in legumes: a case study of Lupinus angustifolius L. FLOWERING LOCUS T homologs, LanFTc1 and LanFTc2

BACKGROUND

The Arabidopsis FLOWERING LOCUS T (FT) gene, a member of the phosphatidylethanolamine binding protein (PEBP) family, is a major controller of flowering in response to photoperiod, vernalization and light quality. In legumes, FT evolved into three, functionally diversified clades, FTa, FTb and FTc. A milestone achievement in narrow-leafed lupin (Lupinus angustifolius L.) domestication was the loss of vernalization responsiveness at the Ku locus. Recently, one of two existing L. angustifolius homologs of FTc, LanFTc1, was revealed to be the gene underlying Ku. It is the first recorded involvement of an FTc homologue in vernalization. The evolutionary basis of this phenomenon in lupin has not yet been deciphered.

RESULTS

Bacterial artificial chromosome (BAC) clones carrying LanFTc1 and LanFTc2 genes were localized in different mitotic chromosomes and constituted sequence-specific landmarks for linkage groups NLL-10 and NLL-17. BAC-derived superscaffolds containing LanFTc genes revealed clear microsyntenic patterns to genome sequences of nine legume species. Superscaffold-1 carrying LanFTc1 aligned to regions encoding one or more FT-like genes whereas superscaffold-2 mapped to a region lacking such a homolog. Comparative mapping of the L. angustifolius genome assembly anchored to linkage map localized superscaffold-1 in the middle of a 15 cM conserved, collinear region. In contrast, superscaffold-2 was found at the edge of a 20 cM syntenic block containing highly disrupted collinearity at the LanFTc2 locus. 118 PEBP-family full-length homologs were identified in 10 legume genomes. Bayesian phylogenetic inference provided novel evidence supporting the hypothesis that whole-genome and tandem duplications contributed to expansion of PEBP-family genes in legumes. Duplicated genes were subjected to strong purifying selection. Promoter analysis of FT genes revealed no statistically significant sequence similarity between duplicated copies; only RE-alpha and CCAAT-box motifs were found at conserved positions and orientations.

CONCLUSIONS

Numerous lineage-specific duplications occurred during the evolution of legume PEBP-family genes. Whole-genome duplications resulted in the origin of subclades FTa, FTb and FTc and in the multiplication of FTa and FTb copy number. LanFTc1 is located in the region conserved among all main lineages of Papilionoideae. LanFTc1 is a direct descendant of ancestral FTc, whereas LanFTc2 appeared by subsequent duplication.

Genome-wide identification and comparison of legume MLO gene family

MLO proteins are highly conserved proteins with seven trans-membrane domains. Specific MLO genes have been linked to plant disease susceptibility. Others are involved in plant reproduction and in root thigmomorphogenesis. Functions of the remaining MLOs are still unknown. Here we performed a genome-wide survey of the MLO family in eight legume species from different clades of the Papillionoideae sub-family. A total of 118 MLO sequences were identified and characterized. Their deduced protein sequences shared the characteristics of MLO proteins. The total number of MLO genes per legume species varied from 13 to 20 depending on the species. Legume MLOs were evenly distributed over their genomes and tended to localize within syntenic blocks conserved across legume genomes. Phylogenetic analysis indicated that these sequences clustered in seven well-defined clades. Comparison of MLO protein sequences revealed 34 clade-specific motifs in the variable regions of the proteins. Comparative analyses of the MLO family between legume species also uncovered several evolutionary differences between the tropical legume species from the Phaseoloid clades and the other legume species. Altogether, this study provides interesting new features on the evolution of the MLO family. It also provides valuable clues to identify additional MLO genes from non-sequenced species.

Genome analysis and avirulence gene cloning using a high-density RADseq linkage map of the flax rust fungus, Melampsora lini

BACKGROUND

Rust fungi are an important group of plant pathogens that cause devastating losses in agricultural, silvicultural and natural ecosystems. Plants can be protected from rust disease by resistance genes encoding receptors that trigger a highly effective defence response upon recognition of specific pathogen avirulence proteins. Identifying avirulence genes is crucial for understanding how virulence evolves in the field.

RESULTS

To facilitate avirulence gene cloning in the flax rust fungus, Melampsora lini, we constructed a high-density genetic linkage map using single nucleotide polymorphisms detected in restriction site-associated DNA sequencing (RADseq) data. The map comprises 13,412 RADseq markers in 27 linkage groups that together span 5860 cM and contain 2756 recombination bins. The marker sequences were used to anchor 68.9 % of the M. lini genome assembly onto the genetic map. The map and anchored assembly were then used to: 1) show that M. lini has a high overall meiotic recombination rate, but recombination distribution is uneven and large coldspots exist; 2) show that substantial genome rearrangements have occurred in spontaneous loss-of-avirulence mutants; and 3) identify the AvrL2 and AvrM14 avirulence genes by map-based cloning. AvrM14 is a dual-specificity avirulence gene that encodes a predicted nudix hydrolase. AvrL2 is located in the region of the M. lini genome with the lowest recombination rate and encodes a small, highly-charged proline-rich protein.

CONCLUSIONS

The M. lini high-density linkage map has greatly advanced our understanding of virulence mechanisms in this pathogen by providing novel insights into genome variability and enabling identification of two new avirulence genes.

Molecular Evolution and Functional Characterization of a Bifunctional Decarboxylase Involved in Lycopodium Alkaloid Biosynthesis

Lycopodium alkaloids (LAs) are derived from lysine (Lys) and are found mainly in Huperziaceae and Lycopodiaceae. LAs are potentially useful against Alzheimer's disease, schizophrenia, and myasthenia gravis. Here, we cloned the bifunctional lysine/ornithine decarboxylase (L/ODC), the first gene involved in LA biosynthesis, from the LA-producing plants Lycopodium clavatum and Huperzia serrata We describe the in vitro and in vivo functional characterization of the L. clavatum L/ODC (LcL/ODC). The recombinant LcL/ODC preferentially catalyzed the decarboxylation of l-Lys over l-ornithine (l-Orn) by about 5 times. Transient expression of LcL/ODC fused with the amino or carboxyl terminus of green fluorescent protein, in onion (Allium cepa) epidermal cells and Nicotiana benthamiana leaves, showed LcL/ODC localization in the cytosol. Transgenic tobacco (Nicotiana tabacum) hairy roots and Arabidopsis (Arabidopsis thaliana) plants expressing LcL/ODC enhanced the production of a Lys-derived alkaloid, anabasine, and cadaverine, respectively, thus, confirming the function of LcL/ODC in plants. In addition, we present an example of the convergent evolution of plant Lys decarboxylase that resulted in the production of Lys-derived alkaloids in Leguminosae (legumes) and Lycopodiaceae (clubmosses). This convergent evolution event probably occurred via the promiscuous functions of the ancestral Orn decarboxylase, which is an enzyme involved in the primary metabolism of polyamine. The positive selection sites were detected by statistical analyses using phylogenetic trees and were confirmed by site-directed mutagenesis, suggesting the importance of those sites in granting the promiscuous function to Lys decarboxylase while retaining the ancestral Orn decarboxylase function. This study contributes to a better understanding of LA biosynthesis and the molecular evolution of plant Lys decarboxylase.

Root trait diversity, molecular marker diversity, and trait-marker associations in a core collection of Lupinus angustifolius

Narrow-leafed lupin (Lupinus angustifolius L.) is the predominant grain legume crop in southern Australia, contributing half of the total grain legume production of Australia. Its yield in Australia is hampered by a range of subsoil constraints. The adaptation of lupin genotypes to subsoil constraints may be improved by selecting for optimal root traits from new and exotic germplasm sources. We assessed root trait diversity and genetic diversity of a core collection of narrow-leafed lupin (111 accessions) using 191 Diversity Arrays Technology (DArT) markers. The genetic relationship among accessions was determined using the admixture model in STRUCTURE. Thirty-eight root-associated traits were characterized, with 21 having coefficient of variation values >0.5. Principal coordinate analysis and cluster analysis of the DArT markers revealed broad diversity among the accessions. An ad hoc statistics calculation resulted in 10 distinct populations with significant differences among and within them (P < 0.001). The mixed linear model test in TASSEL showed a significant association between all root traits and some DArT markers, with the numbers of markers associated with an individual trait ranging from 2 to 13. The percentage of phenotypic variation explained by any one marker ranged from 6.4 to 21.8%, with 15 associations explaining >10% of phenotypic variation. The genetic variation values ranged from 0 to 7994, with 23 associations having values >240. Root traits such as deeper roots and lateral root proliferation at depth would be useful for this species for improved adaptation to drier soil conditions. This study offers opportunities for discovering useful root traits that can be used to increase the yield of Australian cultivars across variable environmental conditions.

Integration of Lupinus angustifolius L. (narrow-leafed lupin) genome maps and comparative mapping within legumes

Narrow-leafed lupin (Lupinus angustifolius L.) has recently been considered a reference genome for the Lupinus genus. In the present work, genetic and cytogenetic maps of L. angustifolius were supplemented with 30 new molecular markers representing lupin genome regions, harboring genes involved in nitrogen fixation during the symbiotic interaction of legumes and soil bacteria (Rhizobiaceae). Our studies resulted in the precise localization of bacterial artificial chromosomes (BACs) carrying sequence variants for early nodulin 40, nodulin 26, nodulin 45, aspartate aminotransferase P2, asparagine synthetase, cytosolic glutamine synthetase, and phosphoenolpyruvate carboxylase. Together with previously mapped chromosomes, the integrated L. angustifolius map encompasses 73 chromosome markers, including 5S ribosomal DNA (rDNA) and 45S rDNA, and anchors 20 L. angustifolius linkage groups to corresponding chromosomes. Chromosomal identification using BAC fluorescence in situ hybridization identified two BAC clones as narrow-leafed lupin centromere-specific markers, which served as templates for preliminary studies of centromere composition within the genus. Bioinformatic analysis of these two BACs revealed that centromeric/pericentromeric regions of narrow-leafed lupin chromosomes consisted of simple sequence repeats ordered into tandem repeats containing the trinucleotide and pentanucleotide simple sequence repeats AGG and GATAC, structured into long arrays. Moreover, cross-genus microsynteny analysis revealed syntenic patterns of 31 single-locus BAC clones among several legume species. The gene and chromosome level findings provide evidence of ancient duplication events that must have occurred very early in the divergence of papilionoid lineages. This work provides a strong foundation for future comparative mapping among legumes and may facilitate understanding of mechanisms involved in shaping legume chromosomes.

Evolution of plant genome architecture

We have witnessed an explosion in our understanding of the evolution and structure of plant genomes in recent years. Here, we highlight three important emergent realizations: (1) that the evolutionary history of all plant genomes contains multiple, cyclical episodes of whole-genome doubling that were followed by myriad fractionation processes; (2) that the vast majority of the variation in genome size reflects the dynamics of proliferation and loss of lineage-specific transposable elements; and (3) that various classes of small RNAs help shape genomic architecture and function. We illustrate ways in which understanding these organism-level and molecular genetic processes can be used for crop plant improvement.

Sequencing Crop Genomes: A Gateway to Improve Tropical Agriculture

Agricultural development in the tropics lags behind development in the temperate latitudes due to the lack of advanced technology, and various biotic and abiotic factors. To cope with the increasing demand for food and other plant-based products, improved crop varieties have to be developed. To breed improved varieties, a better understanding of crop genetics is necessary. With the advent of next-generation DNA sequencing technologies, many important crop genomes have been sequenced. Primary importance has been given to food crops, including cereals, tuber crops, vegetables, and fruits. The DNA sequence information is extremely valuable for identifying key genes controlling important agronomic traits and for identifying genetic variability among the cultivars. However, massive DNA re-sequencing and gene expression studies have to be performed to substantially improve our understanding of crop genetics. Application of the knowledge obtained from the genomes, transcriptomes, expression studies, and epigenetic studies would enable the development of improved varieties and may lead to a second green revolution. The applications of next generation DNA sequencing technologies in crop improvement, its limitations, future prospects, and the features of important crop genome projects are reviewed herein.