Defence genes in Citrus sunki and Poncirus trifoliata: expression constitutive and induced by Phytophthora parasitica. / Genes de defesa de Citrus sunki e Poncirus trifoliata: expressÃo constitutiva e induzida por Phytophthora parasitica

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

Citrus gummosis, caused mainly by Phytophthora parasitica, is one of the most important citrus diseases affecting all production phases. The use of genetic resistance is the best strategy for controlling P. parasitica having a lower impact on the environment. A better understanding of the molecular mechanisms involved in the interaction citrus-Phytophthora spp. would contribute to the elaboration of long term and efficient strategies for the control of this oomycete. The objective of this work was to quantify the constitutive and induced expression of citrus defense genes in response to P. parasitica using real time quantitative RT-PCR. The local and systemic induced expression of the PAL (Phenylalaine ammonia-lyase), POX (Peroxidase), LOX (Lipoxigenase), PR-2(β 1,3-Glucanse) and PR-5 (Osmotin) like genes, involved in the plant pathogen defense, were monitored throughout time in resistant (Poncirus trifoliata) and susceptible (Citrus sunki) plants inoculated with the patogen. The constitutive expression of PR-2- and PR-5-like genes was quantified in P. trifoliata, C. sunki and C. sunki x P. trifoliata hybrids. The expression of PAL, POX, PR-5 like genes was quicker and higher in P. trifoliata than in C. sunki. The local expression of PAL, POX, PR-2 and PR-5 was quicker and higher than the systemic expression for P. trifoliata and C. sunki and for the LOX like gene just in C. sunki. The wounding caused during inoculation induced a high level of expression of all the studied genes, mainly in P. trifoliata. However, the presence of P. parasitica had a significant additive effect on the expression levels of the studied genes, except for the Peroxidase-encoded genes. The results suggest that P. trifoliata could be characterized as resistant to P. parasitica and C. sunki as susceptible by presenting patterns of defense genes expression typicaly of incompatible and compatible interactions, respectively. The presence of PR-2 and PR-5 genes in the genome the C. sunki, P. trifoliata, C. sinensis, C. limonia was confirmed by Southern blot analysis. The multiple hybridization signals obtained are indicative of the occurrence of these genes as a gene family in the genome of these citrus species. The high constitutive expression of the PR-5-like genes was associated with the citrus resistance to P. parasitica and could be, therefore, used to monitor citrus resistance to P. parasitica, working as a biomarker for the selection of promising materials in citrus breeding programs.

ASSUNTO(S)

citrus defence genes expression agronomia marcadores moleculares genetica e melhoramento de plantas phytophthora parasitica

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