Identification of a splicing coactivator gene that affects the production of ochratoxin a in Aspergillus carbonarius

Ochratoxin A is a mycotoxin produced by some fungi species. Among them, Aspergillus carbonarius is considered a powerful producer. Genes involved in the ochratoxin A biosynthesis pathway have been identified in some producer species. However, there are few studies that purpose to identify these genes in A. carbonarius. The use of insertion mutants to identify genes associated with certain properties has been increased in the literature. In this work, the region of T-DNA integration was investigated in one A. carbonarius ochratoxin-defective mutant previously obtained by Agrobacterium tumefaciens-mediated transformation, in order to find an association between interrupted gene and the biosynthesis of ochratoxin A. The integration occurred in a gene that possibly encodes a splicing coactivator protein. The analysis of the relative expression of the splicing coativator gene from A. carbonarius wild type strain in four different media showed high correlation between the transcript levels and the ochratoxin A production.

A ocratoxina A é uma micotoxina frequentemente encontrada em uma grande variedade de produtos alimentares e apresenta efeitos nefrotóxicos e potencial carcinogênico para animais e humanos. É naturalmente produzida por algumas espécies fúngicas, como Aspergillus carbonarius, que é considerado um potente produtor. Apesar disso, o número de estudos que visam identificar genes que são essenciais para a biossíntese de ocratoxina em A. carbonarius é ainda reduzido. Um mutante de A. carbonarius com baixa produção de ocratoxina A previamente obtido por transformação mediada por Agrobacterium tumefaciens foi investigado com o objetivo de encontrar uma associação entre o gene interrompido e a biossíntese desta micotoxina. Os resultados mostraram a ocorrência de uma junção não exata entre o T-DNA e o DNA genômico do fungo durante o evento de integração. A integração do T-DNA no genoma do mutante T188 provocou deleção de 727 nucleotídeos. Esta deleção inclui uma porção final do gene coativador de splicing e uma região não-codificante entre este gene e o gene F-actina. A expressão relativa do gene coativador de splicing na linhagem selvagem cultivada em quatro diferentes meios mostrou associação entre a quantidade de ocratoxina A e os níveis dos transcritos.

Cytogenetic studies in some species of Passiflora L. (Passifloraceae): a review emphasizing Brazilian species

The Passifloraceae is represented by species of tropical and subtropical origin. The Passiflora is the richest genus with approximately 450 species, 200 of them being native to Brazil. Recent karyological studies have reported the basic chromosome number for the Passiflora genus as x = 6, whereas x = 9, x = 10 and x = 12 were established as secondary basic numbers. High rates of fertility occur in most Passiflora species, since both meiotic index and pollen viability are above 90 percent. Unusual meiotic behavior has been described in some taxa. Unviable pollen were observed in some diploids species. The genome size varies from 1.83 to 5.36 pg, and significant interspecific variance has been observed. Studies using the FISH methodology have shown that there are two to three rDNA 45S sites and one 5S site in the species analyzed. In this review, information about the above-mentioned studies is presented and discussed in detail.

A família Passifloraceae é representada por espécies de origem tropical e subtropical. Passiflora é o gênero mais rico, com aproximadamente 450 espécies, cerca de 200 delas nativas do Brasil. Recentes estudos cariológicos têm relatado o número básico de cromossomos para o gênero Passiflora como sendo x = 6, enquanto x = 9, x = 10 e x = 12 foram considerados números básicos secundários. Altas taxas de fertilidade são observadas na maioria das espécies de Passiflora, uma vez que o índice meiótico e a viabilidade polínica apresentam-se acima de 90 por cento.Comportamento meiótico irregular tem sido descrito para alguns taxas. Grãos de pólen inviáveis foram observados em espécies diplóides. O tamanho do genoma varia de 1,83 a 5,36 pg, e variação interespecífica significativa tem sido observada. Estudos usando a metodologia de hibridização in situ (FISH) tem demonstrado haver de dois a três sites de DNAr 45S e um site de DNAr 5S nas espécies analisadas. Nesta revisão, informações sobre os estudos acima mencionados são apresentados e discutidos em detalhes.

Origin, evolution and genome distribution of microsatellites

Microsatellites, or simple sequence repeats (SSRs), have been the most widely applied class of molecular markers used in genetic studies, with applications in many fields of genetics including genetic conservation, population genetics, molecular breeding, and paternity testing. This range of applications is due to the fact that microsatellite markers are co-dominant and multi-allelic, are highly reproducible, have high-resolution and are based on the polymerase chain reaction (PCR). When first introduced, the development of microsatellite markers was expensive but now new and efficient methods of repetitive sequence isolation have been reported, which have led to reduced costs and microsatellite-technology has been increasingly applied to several species, including non-model organisms. The advent of microsatellite markers revolutionized the use of molecular markers but the development of biometric methods for analyzing microsatellite data has not accompanied the progress in the application of these markers, with more effort being need to obtain information on the evolution of the repetitive sequences, which constitute microsatellites in order to formulate models that fit the characteristics of such markers. Our review describes the genetic nature of microsatellites, the mechanisms and models of mutation that control their evolution and aspects related to their genesis, distribution and transferability between taxa. The implications of the use of microsatellites as a tool for estimating genetic parameters are also discussed.

Predicting performance of soybean populations using genetic distances estimated with RAPD markers

In order to verify whether genetic distance (GD) is associated with population mean (PM), genetic variance (GV) and the proportion of superior progenies generated by each cross in advanced generations of selfing (PS), the genetic distances between eight soybean lines (five adapted and three non-adapted) were estimated using 213 polymorphic RAPD markers. The genetic distances were partitioned according to Griffing's Model I Method 4 for diallel analysis, i.e., GDij = GD+ GGDi+ GGDj + SGDij. Phenotypic data were recorded for seed yield and plant height for 25 out of 28 populations of a diallel set derived from the eight soybean lines and evaluated from F2:8 to F2:11 generations. No significant correlation for seed yield was detected between GD and GV, while negative correlations were detected between GD and PM and between GD and PS (r = -0.74** and -0.75**, respectively). Similar results were observed for the correlation between GGDi + GGDj and PM and between GGDi + GGDj and PS (r = -0.78** and -0.80**, respectively). No significant correlation was detected for plant height. The magnitudes of the correlations for seed yield were high enough to allow predictions of the potential of the populations based on RAPD markers

Reciprocal recurrent selection effects on the genetic structure of tropical maize populations assessed at microsatellite loci

A modified reciprocal recurrent selection (RRS) method, which employed one cycle of high-intensity selection, was applied to two tropical maize (Zea mays L.) populations, BR-105 and BR-106, originating the improved synthetics IG-3 and IG-4, respectively. In the present study the effects of this kind of selection on the genetic structure of these populations and their synthetics were investigated at 30 microsatellite (SSR) loci. A total of 125 alleles were revealed. A reduction in the number of alleles was observed after selection, as well as changes in allele frequencies. In nearly 13 percent (BR-105) and 7 percent (BR-106) of the loci evaluated, the changes in allele frequencies were not explained, exclusively due to the effects of genetic drift. The effective population sizes estimated for the synthetics using 30 SSR loci were similar to those theoretically expected after selection. The genetic differentiation (G ST) between the synthetics increased to 77 percent compared with the original populations. The estimated R ST values, a genetic differentiation measure proper for microsatellite data, were similar to those obtained for G ST. Despite the high level of selection applied, the total gene diversity found in the synthetics allows them to be used in a new RRS cycle

Genetic instability of sugarcane plants derived from meristem cultures

The RADP (Random amplified polymorphic DNA) technique was used to detect tissue-culture-induced variations in sugarcane. Plants of the Brazilian variety RB83-5486 propagated via rhizomes and via meristem cultures were studied. The polymorphism rate for 98 RAPD loci was 6.93 percent when the plants derived from meristems. Besides, in order to evaluate the influence of the number of subcultures on the generation of somaclonal variation, field-grown RB83-5486 plants derived from 10 meristems were studied after five subcultivations. Although different rates of polymorphism were observed, there was no direct association with the stage of subcultivation. The analysis of plants of two sugarcane varieties cultivated in vitro from meristems showed that variety RB83-5486 was more unstable than variety SP80-185