Differential gene expression of sweet orange (Citrus sinensis L. Osb.) and mandarin (C. reticulata Blanco) in response to the infection of Xylella fastidiosa

Abstract

The citrus industry is an important activity in the Brazilian agribusiness, and has a budget over than 1.5 billion dollar a year with exportation of concentrated orange juice. However, it has low productivity associated with the increasing number and severity of pests and diseases. Citrus variegated chlorosis, caused by Xylella fastidiosa, affects all varieties of sweet orange and is one more severe citrus disease overall. The disease hás been controlled at field conditions, but there are not tolerant or resistant varieties among the sweet oranges. Tolerant varieties would be the best way to control the disease. Analysis of gene expression of ESTs of sweet orange infected and not infected with X. fastidiosa demonstrated that the infection decreases expression of genes correlated to photosynthesis and increase those associated to adaptation to stress conditions. Thus, functional studies of genes related to infection would allow better understanding of the mechanisms of the X. fastidiosa pathogenicity in sweet orange, or the mechanisms of resistance of mandarins. The main hypothesis of this proposal is that the differential expression of a susceptible (sweet orange) and a resistant genotype (mandarin) may follow up in response to the infection of X. fastidiosa. Therefore, the goal of the proposal is to evaluate the differential expression of set of gene in sweet orange Pera and Ponkan mandarin after infection of the bacteria. The differential expression will be compared after sequencing cDNA libraries generated by suppressive subtractive approaches and real time PCR of selected candidate genes. Both a set of previously selected genes of the CitEST annotation and candidate genes from the subtraction will be evaluated. (AU)