Identificação e expressão de genes da biossíntese do jasmonato na interação entre Theobroma cacao e Moniliophthora perniciosa / Identification and expression of genes associated with jasmonate biosynthesis in the Theobroma cacao and Moniliophthora perniciosa interaction

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Witches broom disease of cacao (Theobroma cacao L.), caused by the basidiomycete Moniliophthora perniciosa is an important disease and the use of resistant varieties is the only economic and environmental long-term solution. Plant hormones are essential in the signaling network involved in the response against a variety of biotic and abiotic stresses. It is well recognized the crucial role of salicylic acid (SA), ethylene (ET) and jasmonate (JA) in plant-pathogen interactions. The mechanism of resistance observed in Theobroma cacao against M. perniciosa does not appear to involve hypersensitivity response mediated by AS signaling, and it is characterized by lower incidence of symptoms and reduction of mycelial growth in resistant material. The response regulated by JA and/or ET is determined by the growth inhibition and a reduction of the colonization of infected tissues by the pathogen, together with an attenuation of symptoms. It is also associated with an induction and production of the protease inhibitors, lytic enzymes and enzymes of secondary metabolism and the genes enconding these enzymes have shown differential expression patterns in samples inoculated with M. perniciosa. It has been recently demonstrated that the production of AS by the fungus M. perniciosa could be associated with a hormonal disorder in the plant, which could therefore help the pathogen in the infective process. Considering this, the hypothesis that JA and/or ET would regulate the interaction of T. cacao with M. perniciosa was formulated in order to be tested by this research work. It is known that the transcription of genes encoding the enzymes of the JA biosynthesis pathway is induced by exogenous application of methyl jasmonate (MJ) and by pathogen, thus, in order to verify the involvement of JA in defense response of cocoa, sequences of genes that encode the enzymes of the JA biosynthesis pathway were isolated, identified, classified and had their identity confirmed by sequencing, and relative quantitative gene expression were evaluated in susceptible P7and resistant CAB 214plants of T. cacao. In addition genes Sams, Accox, Pal , Jaz and Della, were evaluated in experiments with application of inducers (AS, ET and MJ) and inoculation with M. perniciosa. Analysis of relative gene expression by RT-qPCR were conducted and P7seems to have the expression of jasmonate biosynthesis genes in a more intense and more specific manner when treated with MJ, while CAB 214shows an earlier yet lower response suggesting that the mechanism of positive regulation by the exogenous application of MJ also occurs in T. cacao. For the inoculation, the gene expression results suggest a difference in the transcriptional response from inoculation with M. perniciosa between P7and CAB 214in T. cacao. The effect of AS produced by the fungus may not have antagonistic effects in resistant materials such as CAB 214, as indicated by the increase of the transcription of Aos gene that encodes the main enzyme involved in JA biosynthesis, so the defense responses of CAB 214is possibly triggered by JA signaling, because the central role of AOS in its biosynthesis, and may be part of synergistic ET signaling, indicated by high Samsi expression in resistance material

ASSUNTO(S)

vassoura-de-bruxa plant hormones interação planta-patógeno plant-pathogen interaction witches broom disease hormônios vegetais

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