Cultivated peanut (Arachis hypogaea) is an allotetraploid with closely related subgenomes of a total size of ∼2.7 Gb. This makes the assembly of chromosomal pseudomolecules very challenging. As a ...foundation to understanding the genome of cultivated peanut, we report the genome sequences of its diploid ancestors (Arachis duranensis and Arachis ipaensis). We show that these genomes are similar to cultivated peanut's A and B subgenomes and use them to identify candidate disease resistance genes, to guide tetraploid transcript assemblies and to detect genetic exchange between cultivated peanut's subgenomes. On the basis of remarkably high DNA identity of the A. ipaensis genome and the B subgenome of cultivated peanut and biogeographic evidence, we conclude that A. ipaensis may be a direct descendant of the same population that contributed the B subgenome to cultivated peanut.
The Root-Knot Nematode (RKN), Meloidogyne arenaria, significantly reduces peanut grain quality and yield worldwide. Whilst the cultivated species has low levels of resistance to RKN and other pests ...and diseases, peanut wild relatives (Arachis spp.) show rich genetic diversity and harbor high levels of resistance to many pathogens and environmental constraints. Comparative transcriptome analysis can be applied to identify candidate resistance genes.
Transcriptome analysis during the early stages of RKN infection of two peanut wild relatives, the highly RKN resistant Arachis stenosperma and the moderately susceptible A. duranensis, revealed genes related to plant immunity with contrasting expression profiles. These included genes involved in hormone signaling and secondary metabolites production and also members of the NBS-LRR class of plant disease resistance (R) genes. From 345 NBS-LRRs identified in A.duranensis reference genome, 52 were differentially expressed between inoculated and control samples, with the majority occurring in physical clusters unevenly distributed on eight chromosomes with preferential tandem duplication. The majority of these NBS-LRR genes showed contrasting expression behaviour between A. duranensis and A. stenosperma, particularly at 6 days after nematode inoculation, coinciding with the onset of the Hypersensitive Response in the resistant species. The physical clustering of some of these NBS-LRR genes correlated with their expression patterns in the contrasting genotypes. Four NBS-LRR genes exclusively expressed in A. stenosperma are located within clusters on chromosome Aradu. A09, which harbors a QTL for RKN resistance, suggesting a functional role for their physical arrangement and their potential involvement in this defense response.
The identification of functional novel R genes in wild Arachis species responsible for triggering effective defense cascades can contribute to the crop genetic improvement and enhance peanut resilience to RKN.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Fungal foliar diseases can severely affect the productivity of the peanut crop worldwide. Late leaf spot is the most frequent disease and a major problem of the crop in Brazil and many other tropical ...countries. Only partial resistance to fungal diseases has been found in cultivated peanut, but high resistances have been described on the secondary gene pool.
To overcome the known compatibility barriers for the use of wild species in peanut breeding programs, we used an induced allotetraploid (
×
)
, as a donor parent, in a successive backcrossing scheme with the high-yielding Brazilian cultivar IAC OL 4. We used microsatellite markers associated with late leaf spot and rust resistance for foreground selection and high-throughput SNP genotyping for background selection.
With these tools, we developed agronomically adapted lines with high cultivated genome recovery, high-yield potential, and wild chromosome segments from both
and
conferring high resistance to late leaf spot and rust. These segments include the four previously identified as having QTLs (quantitative trait loci) for resistance to both diseases, which could be confirmed here, and at least four additional QTLs identified by using mapping populations on four generations.
The introgression germplasm developed here will extend the useful genetic diversity of the primary gene pool by providing novel wild resistance genes against these two destructive peanut diseases.
Peanut is a crop of the Kayabi tribe, inhabiting the Xingu Indigenous Park, Brazil. Morphological analysis of Xingu accessions showed variation exceeding that described for cultivated peanuts. This ...raised questions as to the origin of the Xingu accessions: are they derived from different species, or is their diversity a result of different evolutionary and selection processes? To answer these questions, cytogenetic and genotyping analyses were conducted. The karyotypes of Xingu accessions analyzed are very similar to each other, to an
A. hypogaea
subsp.
fastigiata
accession and to the wild allotetraploid
A. monticola
. The accessions share the number and general morphology of the chromosomes; DAPI
+
bands; 5S and 45S rDNA loci distribution and a high genomic affinity with
A. duranensis
and
A. ipaënsis
genomic probes. However, the number of CMA
3
+
bands differs from those determined for
A. hypogaea
and
A. monticola
, which are also different from each other. SNP genotyping grouped all
Arachis
allotetraploids into four taxonomic groups: Xingu accessions were closer to
A. monticola
and
A. hypogaea
subsp.
hypogaea
. Our data suggests that the morphological diversity within these accessions is not associated with a different origin and can be attributed to morphological plasticity and different selection by the Indian tribes.
We have previously described a bioinformatics pipeline identifying comparative anchor-tagged sequence (CATS) loci, combined with design of intron-spanning primers. The derived anchor markers defining ...the linkage position of homologous genes are essential for evaluating genome conservation among related species and facilitate transfer of genetic and genome information between species. Here we validate this global approach in the common bean and in the AA genome complement of the allotetraploid peanut. We present the successful conversion of approximately 50% of the bioinformatics-defined primers into legume anchor markers in bean and diploid Arachis species. One hundred and four new loci representing single-copy genes were added to the existing bean map. These new legume anchor-marker loci enabled the alignment of genetic linkage maps through corresponding genes and provided an estimate of the extent of synteny and collinearity. Extensive macrosynteny between Lotus and bean was uncovered on 8 of the 11 bean chromosomes and large blocks of macrosynteny were also found between bean and Medicago. This suggests that anchor markers can facilitate a better understanding of the genes and genetics of important traits in crops with largely uncharacterized genomes using genetic and genome information from related model plants.
Simple sequence repeats (SSR), also known as microsatellites, have been extensively used as molecular markers due to their abundance and high degree of polymorphism. We have developed a simple to use ...web software, called WebSat, for microsatellite molecular marker prediction and development. WebSat is accessible through the Internet, requiring no program installation. Although a web solution, it makes use of Ajax techniques, providing a rich, responsive user interface. WebSat allows the submission of sequences, visualization of microsatellites and the design of primers suitable for their amplification. The program allows full control of parameters and the easy export of the resulting data, thus facilitating the development of microsatellite markers.
The web tool may be accessed at http://purl.oclc.org/NET/websat/
‘IAC Sempre Verde’ is a medium-seeded runner-type peanut highly resistant to late leaf spot and rust, the main diseases in peanut cultivation in Brazil. The newly released cultivar showed remarkable ...yield advantage over controls when diseases were not controlled and represents the first possibility for peanut cultivation under “Organic” management.
BRS 425 is a high-oleic runner peanut cultivar related to wild ancestral parents, partially resistant to early and late leaf spot and spotted wilt. It is large-seeded and contains 46% oil. BRS 425 is ...adapted to the main peanutproducing regions of Brazil.
Cultivated peanut, Arachis hypogaea L., is an economically important species. It is very susceptible to different stresses to which wild species are mostly resistant. Foliar diseases, such as late ...leaf spot (LLS) caused by the fungus Cercosporidium personatum, and rust caused by the fungus Puccinia arachidis, are responsible for decrease in plant growth and productivity. The peanut wild relative Arachis stenosperma accession V10309 was identified as resistant to a number of pests and diseases, including LLS and rust. Aiming to better understand the mechanisms of resistance of A. stenosperma to C. personatum and P. arachidis, determine initial key steps of the plant–pathogen interaction and to contribute for studies on genes involved in this interaction, ultrastructural analysis was performed on leaves of A. stenosperma V10309 (wild, resistant) and A. hypogaea cv. IAC‐Tatu (cultivated, susceptible) inoculated with C. personatum or P. arachidis. For both fungal species, adhesion, germination of spores and hyphal proliferation occurred in both species but was more limited and later in A. stenosperma than in A. hypogaea, and no successful penetration was observed in the former. These data suggest that in A. stenosperma, infection is hampered at the stage of penetration. This is the first morphological description of the first hours of the interaction of plant pathogenic fungi and the resistant wild species A. stenosperma.
Peanut is an important legume crop. Although it has high levels of morphological diversity, it lacks geneticvariability and sources of disease resistance. The transference of resistance genes from ...wild species is difficult due to thedifferent ploidy level of the wild and cultivated species. Recently, amphidiploids have been produced that can be used asbridges to introgress wild genes. Molecular markers are useful to pyramidize desirable genes and track them throughgenerations of backcrossings. Molecular markers based on Resistance Gene Analogs have improved chances to be present inor linked to resistance gene loci. This study describes the development and genotyping of molecular markers based onresistance gene motifs. Specific primers were designed based on unique sequences of an Arachis RGA dataset. The identity ofthe amplified polymorphic bands was confirmed by sequencing. These markers were genotyped on a F2 population thatsegregates for resistance to biotic stress types.
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