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Main conclusionOpposing changes in the abundance of satellite DNA and long terminal repeat (LTR) retroelements are the main contributors to the variation in genome size and heterochromatin amount in Arachis diploids.The South American genus Arachis (Fabaceae) comprises 83 species organized in nine taxonomic sections. Among them, section Arachis is characterized by species with a wide genome and karyotype diversity. Such diversity is determined mainly by the amount and composition of repetitive DNA. Here we performed computational analysis on low coverage genome sequencing to infer the dynamics of changes in major repeat families that led to the differentiation of genomes in diploid species (x = 10) of genus Arachis, focusing on section Arachis. Estimated repeat content ranged from 62.50 to 71.68% of the genomes. Species with different genome composition tended to have different landscapes of repeated sequences. Athila family retrotransposons were the most abundant and variable lineage among Arachis repeatomes, with peaks of transpositional activity inferred at different times in the evolution of the species. Satellite DNAs (satDNAs) were less abundant, but differentially represented among species. High rates of evolution of an AT-rich superfamily of satDNAs led to the differential accumulation of heterochromatin in Arachis genomes. The relationship between genome size variation and the repetitive content is complex. However, largest genomes presented a higher accumulation of LTR elements and lower contents of satDNAs. In contrast, species with lowest genome sizes tended to accumulate satDNAs in detriment of LTR elements. Phylogenetic analysis based on repetitive DNA supported the genome arrangement of section Arachis. Altogether, our results provide the most comprehensive picture on the repeatome dynamics that led to the genome differentiation of Arachis species.

Fil: Seijo, José Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina

Apomixis, a clonal plant reproduction by seeds, is controlled in Paspalum spp. by a single locus which is blocked in terms of recombination. Partial sequence analysis of the apomixis locus revealed structural features of heterochromatin, namely the presence of repetitive elements, gene degeneration, and de-regulation. To test the epigenetic control of apomixis, a study on the distribution of cytosine methylation at the apomixis locus and the effect of artificial DNA demethylation on the mode of reproduction was undertaken in two apomictic Paspalum species. The 5-methylcytosine distribution in the apomixis-controlling genomic region was studied in P. simplex by methylation-sensitive restriction fragment length polymorphism (RFLP) analysis and in P. notatum by fluorescene in situ hybridization (FISH). The effect of DNA demethylation was studied on the mode of reproduction of P. simplex by progeny test analysis of apomictic plants treated with the demethylating agent 5’-azacytidine. A high level of cytosine methylation was detected at the apomixis-controlling genomic region in both species. By analysing a total of 374 open pollination progeny, it was found that artificial demethylation had little or no effect on apospory, whereas it induced a significant depression of parthenogenesis. The results suggested that factors controlling repression of parthenogenesis might be inactivated in apomictic Paspalum by DNA methylation. Results presented in this work show for the first time partial phenotype reversion in a natural apomictic plant by an artificial epigenetic landscape modification.

Fil: Samoluk, Sergio Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina

Over the past few decades, peanut smut, caused by Thecaphora frezzii, has evolved from an emerging disease to a major global threat to peanut production. However, critical knowledge gaps persist regarding the anatomical pathways and host responses involved in infection, colonization, and sporulation. This study examines the pathosystem and histopathology of the biotrophic phase of T. frezzii in the susceptible cv. Granoleico. Anatomical analyses were conducted using light microscopy, confocal laser scanning, and scanning electron microscopy. Our findings reveal that T. frezzii enters the host through the peg rather than the ovary tip, invading during the R2-subterranean phase. Fruit colonization occurs at the R3-stage when the mechanical layer between the mesocarp and endocarp has not yet formed. Hyphal entry into the seed takes place between the R3-medium and R3-late pod stages via the funiculus, leading to extensive seed coat colonization without penetrating the embryo. Once inside, hyperplasia and hypertrophy are triggered, coinciding with teliospore formation. Teliosporogenesis disrupts nutrient translocation, arresting embryo development. The hyphae colonize tissues intracellularly, utilizing living cells of the vascular bundles and following the peanut’s photoassimilate transport pathway. Investigating these structural responses in phenotypically contrasting peanut genotypes may provide key insights into the anatomical barriers and defense mechanisms that determine disease susceptibility and resistance, ultimately contributing to the development of resistant cultivars.

Liolaemus is the most specious genus of the Squamata lizards in South America, presenting exceptional evolutionary radiation and speciation patterns. This recent diversification complicates the formal taxonomic treatment and the phylogenetic analyses of this group, causing relationships among species to remain controversial. Here we used Next-Generation Sequencing to do a comparative analysis of the structure and organization of the complete mitochondrial genomes of three differently related species of Liolaemus and with different reproductive strategies and ploidy levels. The annotated mitochondrial genomes of ca. 17 kb are the first for the Liolaemidae family. Despite the high levels of sequence similarity among the three mitochondrial genomes over most of their lengths, the comparative analyses revealed variations at the stop codons of the protein coding genes and the structure of the tRNAs among species. The presence of a non-canonical dihydrouridine loop is a novelty for the pleurodonts iguanians. But the highest level of variability was observed in two repetitive sequences of the control region, which were responsible for most of the length heterogeneity of the mitochondrial genomes. These tandem repeats may be useful markers to analyze relationships of closely related species of Liolaemus and related genera and to conduct population and phylogenetic studies.

Fil: Samoluk, Sergio Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Botánica del Nordeste. Universidad Nacional del Nordeste. Facultad de Ciencias Agrarias. Instituto de Botánica del Nordeste; Argentina

Species of section Arachis with x = 10 are important for peanut breeding and have been organized in five different genomes (A, B, D, F and K). The few available estimates of the DNA content are inconsistent and hampered the understanding of the evolutionary trends and in decision making for genomic studies of the group. Considering that, the objectives of this research were to measure the DNA content for all available (26) species and to make evolutionary inferences at the diploid and tetraploid level for section Arachis. The 2C values obtained by flow cytometry ranged from 2.55 to 3.22 pg among the diploid species. The annual species belonging to different genomes tend to have different genome sizes. However, the 2C values of the perennial species of the A genome were distributed almost along the whole range of genome sizes here observed. The distribution of 2C values partially support the genome arrangement proposed for the section. The comparisons of 2C values with karyotype parameters suggests that changes in DNA content have been proportionally distributed among the chromosome arms, and that the heterochromatic fractionwas not directly involved in that changes. Within the A genome, the annual species has lowerDNAcontent than the perennial ones, according to the nucleotype hypothesis. However, the lack of significant relationships with geoclimatic variables suggests that there are many intrinsic factors determining particular ecological roles of the DNA content in the different lineages of section Arachis. The constancy of the Cx values observed in the polyploids compared to those of the parental species suggests that the allopolyploidization event that originated the cultivated peanut did not induce significant changes in the genome size.

Peanut is an allotetraploid (2n = 2x = 40, AABB) of recent origin. Arachis duranensis and A. ipaënsis, the most probable diploid ancestors of the cultigen, and several other wild diploid species with different genomes (A, B, D, F and K) are used in peanut breeding programs. However, the genomic relationships and the evolutionary pathways of genome differentiation of these species are poorly understood. We performed a sequence-based phylogenetic analysis of the L1 reverse transcriptase and estimated its representation and chromosome distribution in species of five genomes and three karyotype groups with the aim of contributing to the knowledge of the genomic structure and evolution of peanut and wild diploid relatives. All the isolated rt fragments were found to belong to plant L1 lineage and were named ALI. The best supported phylogenetic groups were not concordant with the genomes or karyotype groups. The copy number of ALI sequences was higher than the expected one for plants and directly related to genome size. FISH experiments revealed that ALI is mainly located on the euchromatin of interstitial and distal regions of most chromosome arms. Divergence of ALI sequences would have occurred before the differentiation of the genomes and karyotype groups of Arachis. The representation and chromosome distribution of ALI in peanut was almost additive of those of the parental species suggesting that the spontaneous hybridization of the two parental species of peanut followed by chromosome doubling would not have induced a significant burst of ALI transposition.