Orelvis Portal

Sugarcane genes differentially expressed in response to Puccinia melanocephala infection: identification and transcript profiling

Brown rust caused by the fungus Puccinia melanocephala is a major disease of sugarcane (Saccharum spp.). A sugarcane mutant, obtained by chemical mutagenesis of the susceptible variety B4362, showed a post-haustorial hypersensitive response (HR)-mediated resistance to the pathogen and was used to identify genes differentially expressed in response to P. melanocephala via suppression subtractive hybridization (SSH). Tester cDNA was derived from the brown rust-resistant mutant after inoculation with P. melanocephala, while driver cDNAs were obtained from the non-inoculated resistant mutant and the inoculated susceptible donor variety B4362. Database comparisons of the sequences of the SSH recombinant clones revealed that, of a subset of 89 non-redundant sequences, 88% had similarity to known functional genes, while 12% were of unknown function. Thirteen genes were selected for transcript profiling in the resistant mutant and the susceptible donor variety. Genes involved in glycolysis and C4 carbon fixation were up-regulated in both interactions probably due to disturbance of sugarcane carbon metabolism by the pathogen. Genes related with the nascent polypeptide associated complex, post-translational proteome modulation and autophagy were transcribed at higher levels in the compatible interaction. Up-regulation of a putative l-isoaspartyl O-methyltransferase S-adenosylmethionine gene in the compatible interaction may point to fungal manipulation of the cytoplasmatic methionine cycle. Genes coding for a putative no apical meristem protein, S-adenosylmethionine decarboxylase, non-specific lipid transfer protein, and GDP-l-galactose phosphorylase involved in ascorbic acid biosynthesis were up-regulated in the incompatible interaction at the onset of haustorium formation, and may contribute to the HR-mediated defense response in the rust-resistant mutant.

A green fluorescent protein-transformed Mycosphaerella fijiensis strain shows increased aggressiveness on banana

The fungal pathogen Mycosphaerella fijiensis, causal agent of black leaf streak disease of bananas and plantains, was transformed with a green fluorescent protein-carrying construct by using a restriction enzyme-mediated integration methodology. A quantitative polymerase chain reaction was adapted to estimate transgene copy number and pathogenicity assays with three banana genotypes with dissimilar reactions to M. fijiensis infection were performed to characterize the transformants. Transgene insertion varied from one to five copies per genome among four random selected transformants. All M. fijiensis strains produced typical symptoms of the black leaf streak disease on the three banana genotypes assayed. Interestingly, the GFP-18 transformant showed increased aggressiveness on susceptible ‘Grande naine’ and resistant ‘Yangambi km5’ plants demonstrating that mutation events in M. fijiensis can increase virulence.

Early regulation of primary metabolism, antioxidant, methyl cycle and phenylpropanoid pathways during the Mycosphaerella fijiensis-Musa spp. interaction

Black leaf streak disease (BLSD) caused by Mycosphaerella fijiensis is considered the most destructive and costly foliar disease that affects bananas and plantains. In spite of some recent progress regarding the study of M. fijiensis-Musa spp. interaction, there is still limited information for this pathosystem. To gain insights into the molecular mechanisms behind the M. fijiensis-Musa spp. interaction, gene expression and biochemical analysis related with primary metabolism, methyl cycle, antioxidant and phenylpropanoid pathways were conducted. Early screening of the resistant cultivar (cv.) ‘Calcutta 4’ (Musa AA) and the susceptible cv. ‘Grande naine’ (Musa AAA) plants infected with M. fijiensis was effective at looking for defense-related genes. Quantitative PCR experiments showed up-regulation of Photosystem I reaction center subunit N chloroplastic-like (primary metabolism) and S-adenosyl-L-methionine synthetaste (methyl cycle) genes in the incompatible interaction, as well as down-regulation of the phenylpropanoid pathway genes in the susceptible cv. ‘Grande naine’ as main finding of this study. Improved knowledge concerning the M. fijiensis-Musa spp. interaction could help to establish innovative approaches for plant breeding programs against BLSD.

Aggressiveness of Cuban Papaya ringspot virus Isolates on Carica papaya L. cv. Maradol Roja under Greenhouse Conditions

Aggressiveness of Cuban Papaya ringspot virus Isolates on Carica papaya L. cv. Maradol Roja under Greenhouse Conditions Carica papaya is a major fruit crop in tropical and subtropical regions; however, its production has several constraints. Papaya ringspot virus (PRSV) is the most important pathogen affecting papaya plantations. Symptoms induced by a known PRSV isolate on papaya plants after mechanical inoculation were described to elaborate an evaluation scale under greenhouse conditions. The aggressiveness of 24 Cuban PRSV isolates was determined by assessing symptom severity induced on papaya plants cv. Maradol roja under greenhouse conditions. An evaluation scale of 0 to 6 scores was elaborated based on the observations of PRSV symptom progress. Symptoms induced by Cuban PRSV isolates included vein clearing, mottling and swelling zones on the adaxial leaf surface, slight deformation of young leaves and distortion. PRSV isolates from Nueva Paz, Guines, and San Jose de Las Lajas in the west, Sancti Spiritus in the center, and Palma Soriano and Puerto Padre in the east of the country were the most aggressive according to their area under the disease progress curve values. Knowledge about the aggressiveness of this virus is crucial for selecting PRSV isolates to implement management strategies and papaya breeding programs in Cuba.