Cláudia M. Bellato

In Vitro Production of Biotrophic-Like Cultures of Crinipellis perniciosa , the Causal Agent of Witches’ Broom Disease of Theobroma cacao

Witches’ broom disease (WBD) of cacao, caused by the hemibiotrophic fungus, Crinipellis perniciosa, exhibits a succession of symptoms that are caused by the biotrophic phase of the fungus. However, the study of this biotrophic phase is limited by its exclusive growth inside the plant or in the presence of callus. Here we report for the first time a method for the growth and maintenance of the biotrophic-like phase of C. perniciosa on a defined medium with metabolites found in the diseased tissues. Our results suggest that glycerol is a key carbon source for this interaction. This is a crucial achievement toward understanding the biology of this fungus during the infectious phase of WBD.

Genetic control of lysine metabolism in maize endosperm mutants

The capacity of three maize endosperm opaque mutants (o10, o11 and o13) to accumulate soluble lysine in the seed in relation to their wildtype counterpart, W22+, was investigated. The W22o13 and W22o11 mutants exhibited 278% and 186% increases in soluble lysine, respectively, while for W22o10, a 36% decrease was observed, compared with the wildtype. A quantitative and qualitative study of the N constituents of the endosperm has been conducted and data obtained for the total protein, non-protein N, soluble amino acids, albumins / globulins, zeins and glutelins present in the seed of the mutants. Following 2D-PAGE, a total of 38 different forms of zein polypeptides were detected and considerable differences were noted between the three mutant lines. The metabolism of lysine was also studied by analysis of the enzymes aspartate kinase, homoserine dehydrogenase, lysine 2-oxoglutarate reductase and saccharopine dehydrogenase, which exhibited major changes in activity, depending on the genotype, suggesting that the mutant genes may have distinct regulatory activities.

Telomere and microsatellite primers reveal diversity among Sclerotinia sclerotiorum isolates from Brazil

Sclerotinia sclerotiorum, the causal agent of white mold, is a problem of winter bean (Phaseolus vulgaris) production in Brazil under center-pivot irrigation. Isolates of S. sclerotiorum were obtained from a center-pivot-irrigated field near Guaira-SP, Brazil. Mycelial compatibility group (MCG) studies revealed the presence of only two MCG. PCR/RFLP analysis of the ITS1-5.8S-ITS2 ribosomal subunit regions of these field isolates of S. sclerotiorum failed to show any genetic differences between these two MCGs. DNA amplification with a chromosomal telomere sequence-based primer and one microsatellite primer revealed genetic polymorphisms among isolates within the same MCG. Isolates taken from beans and two other crops from another region of Brazil showed the same two MCG and had identical banding patterns for the telomere and microsatellite primers. These findings support the use of telomere sequence-based primers for revealing genotypic differences among S. sclerotiorum isolates.

Genetic analyses of Rhizoctonia solani isolates from Phaseolus vulgaris grown in the Atlantic Rainforest Region of São Paulo, Brazil

Rhizoctonia solani isolates obtained from common beans (Phaseolus vulgaris) grown in the mountainous Atlantic Rainforest (Mata Atlântica) region of Sao Paulo, Brazil, were analyzed to determine their genetic diversity using internal transcribed spacer (ITS), microsatellite and telomere sequence-based PCR primers. Restriction digestion of the ITS1/5.8S/ITS2 ribosomal regions yielded unique banding patterns specific for AG4 and its subgroups. The ITS restriction digestion (ITS/RFLP), telomere and microsatellite primers identified five to 11 genotypes within the isolates of R. solani. While all isolates were pathogenic on beans, there was no correlation found between genotypic differences and pathogenicity. The different PCR primers revealed a number of isolates that were genetically similar. Some of these genetic groups were supported by more than one of the primers utilized in this study, thus confirming their relationship.

Accurate Determination of Genetic Identity for a Single Cacao Bean, Using Molecular Markers with a Nanofluidic System, Ensures Cocoa Authentication

Cacao (Theobroma cacao L.), the source of cocoa, is an economically important tropical crop. One problem with the premium cacao market is contamination with off-types adulterating raw premium material. Accurate determination of the genetic identity of single cacao beans is essential for ensuring cocoa authentication. Using nanofluidic single nucleotide polymorphism (SNP) genotyping with 48 SNP markers, we generated SNP fingerprints for small quantities of DNA extracted from the seed coat of single cacao beans. On the basis of the SNP profiles, we identified an assumed adulterant variety, which was unambiguously distinguished from the authentic beans by multilocus matching. Assignment tests based on both Bayesian clustering analysis and allele frequency clearly separated all 30 authentic samples from the non-authentic samples. Distance-based principle coordinate analysis further supported these results. The nanofluidic SNP protocol, together with forensic statistical tools, is sufficiently robust to establish authentication and to verify gourmet cacao varieties. This method shows significant potential for practical application.

The induction of differentially expressed proteins of Xylella fastidiosa with citrus extract

An in vitro system was developed to induce and identify Xylella fastidiosa proteins that were differentially expressed in the presence of callus-derived extracts from its host, the citrus cultivar Pera. To optimize the induction, we first developed a single culture medium for the growth of both, host and bacteria. This medium, CPXPm7, which mimics the citrus xylem sap, showed that X. fastidiosa at 72 h post-incubation had 108 colony forming units mL-1, while Pera cells had the highest fresh weight content (0.79 g). After testing various methods of co-cultivation of the bacteria and host callus grown in this single medium, the best induction procedure was to grow X. fastidiosa in a solid medium amended with an extract of Pera callus grown in CPXPm7. Analysis, by two-dimensional electrophoresis, of the X. fastidiosa proteins (120 µg of total proteins) grown in the presence of Pera callus extract revealed 414 differentially expressed protein spots when compared to the protein profile obtained in the absence of the extract. The system developed in this study improves the induction and analysis of differentially expressed proteins of X. fastidiosa, which may be involved in pathogenicity.

Assessment of four different detergents used to extract membrane proteins from Xylella fastidiosa by two-dimensional electrophoresis

Four different detergents, ASB 14, SB 3-10, CHAPS and Triton X100, were utilized to determine the optimal detergent for the solubilization of membrane proteins from the phytopathogenic bacterium Xylella fastidiosa. These proteins were differentially solubilized in distinct buffers containing the detergent and subjected to bidimensional electrophoresis within the non-linear pH range of 3-10. The detergents ASB 14 and SB 3-10 were the most effective revealing 221 and 157 spots, respectively. CHAPS and Triton X100 were less effective and revealed only 72 and 43 spots, respectively. MALDI-TOF tryptic peptide mass fingerprinting of 18 excised proteins from the ASB 14 treatment revealed that 83% were membrane proteins and that the theoretical efficiency of solubilization for ASB 14 was estimated to be 87%. This study demonstrates the effectiveness of the detergent ASB 14 for the solubilization of membrane proteins from the bacterium X. fastidiosa.

Variation in phytate accumulation in common bean (Phaseolus vulgaris L.) fruit explants

O fosforo e armazenado na forma de fitato nas sementes, o qual forma complexos estaveis e insoluveis com minerais e proteinas, conferindo efeito antinutriente. A sintese de fitato foi estudada em cultivo de explantes de fruto de feijao in vitro sob diferentes concentracoes de sacarose, fosforo (P), mio-inositol, acido abscisico (ABA), glutamina e metionina. Fixada a concentracao destes compostos, testou-se os diferentes tempos de cultivo (0, 3, 6 e 9 dias). A variacao no acumulo de fitato ocorreu na presenca de sacarose, mio-inositol, P e ABA nas diferentes concentracoes e tempos testados. O acumulo mais efetivo de fitato ocorreu na presenca de mio-inositol e P. O acumulo de P variou menos do que fitato em todos os tratamentos. Em conclusao, P, sacarose, ABA e mio-inositol causaram aumento no fitato acumulado nas sementes, mostrando que foi possivel alterar a sintese de fitato em cultivo de explantes de fruto de feijao.

Utilization of the Etest assay for comparative antibiotic susceptibility profiles of citrus variegated Chlorosis and Pierce's disease strains of Xylella fastidiosa.

Xylella fastidiosa has a wide host range. Isolates of this bacterium that cause diseases in citrus (CVC) and grapes (PD) share 98% genome homology, and 95.7% amino acid identity. Drug resistance genes show a higher level of divergence and may be involved in the X. fastidiosa–host interaction. Antibiotic susceptibility of CVC and PD strains were compared utilizing the Etest strip method (AB Biodisk). Etest is applicable for fastidious slow-growing organisms due to its reproducibility. Results showed that the CVC strain was resistant to bacitracin, cefotaxime, and trimethoprim, and susceptible to chloramphenicol, erythromycin, gentamicin, kanamycin, streptomycin, and tetracycline. The PD strain was susceptible to all tested antibiotics, except kanamycin and trimethoprim. Both isolates produced a class C β-lactamase. These data support previous antibiotic studies and gene discrepancies found in the sequencing data of PD and CVC strains. These results demonstrate the efficacy of utilizing Etest assays for X. fastidiosa strains.

Genotypic analysis of Xylella fastidiosa isolates from different hosts using sequences homologous to the Xanthomonas rpf genes

SUMMARY This is the first report of a genotypic analysis of the phytopathogenic bacteria Xylella fastidiosa (Xf) using differences within intra- and intergenic regions of pathogenic genes. Orthologous sequences from the genome of Xf were identified for genes involved in the regulation of pathogenicity factors (rpf) from Xanthomonas campestris pv. campestris (Xcc). While the rpf genes were conserved, the chromosomal region revealed differences in gene sizes and intergenic spacings and a major translocational event when compared to Xcc. Primers were designed to amplify three regions: the intragenic region of rpfA (2354 bp), the intergenic region between rpfA and rpfB (5772 bp), and the intergenic region between rpfC and rpfF (2314 bp). Amplicons were obtained for all three regions from 32 of the 33 Xf isolates tested from citrus, grape, coffee, plum, hibiscus and periwinkle. Three Xcc isolates from cruciferous plants only generated PCR products for the rpfC-F region. Cleaved amplified polymorphic sequences (CAPS) (Taq(alpha)I) revealed differential banding profiles for the rpfA-B and rpfC-F regions. Xylella isolates were separated into seven groups via rpfA-B, of which five contained only citrus, while the other two had citrus, grape and coffee, and citrus, coffee, plum and hibiscus isolates. rpfC-F separated the isolates into three host-related groups. Citrus, coffee and hibiscus isolates formed one group, while the other two groups were comprised solely of grape and plum isolates. Xcc isolates formed an out-group. In silico analysis supports these results, which reveal the potential of the rpf genes for genotypic analysis of Xylella fastidiosa.