Study of the metagenomics technique for the analysis of non-cultivated plant pathogens

Abstract

The citrus industry is one of the most remarkable activities in the Brazilian agribusiness, from which the São Paulo state is the main producer of orange and frozen concentrated orange juice in the world. The low yield in Brazil (in average, 2 boxes/plant/year) is clearly associated to the simultaneous raise in the incidence of diseases and pests and, as a consequence, in the production costs. In the past twenty years, various diseases and pests with economical importance have been reported in Brazil, such as CVC (citrus variegated chlorosis), leprosis, black spot, sudden death, citrus leaf miner, etc. In addition, recently (in 2004) the huanglongbing (HLB, ex-greening) was found to occur in Brazil (São Paulo state). In fact, HLB is frequently considered the most important citrus disease in the world. Extremely aggressive and destructive to citrus, the disease is caused by the phloem-limited, non-cultivated bacterium Candidatus Liberibacter spp, which causes damages such as chlorosis, leaf and fruit drop, fruit deformation, and low production. Additionaly, the bacterium is vectored by a psyllid (Diaphorina citri), which is wide spread in Brazil. This proposal seeks to enlarge the knowledge on the disease regarding the biology of its causal agent by investigating novel genes, by using the metagenomics, a technique that permits a partial genomic characterization of non-cultivated organisms. Interestingly, only a few of its genes (<10) have been deposited in public databases so far, which indicates a possibility of gaining critical information on novel genes as well as on new potential targets for diagnostics, for instance. This proposal integrates the "Projeto Temático - FAPESP" and represents a multidisciplinary effort that involves various work groups in the São Paulo State. Finally, this "new frontiers" proposal intends to allow the training of a researcher in a laboratory located in the University of Wisconsin (Dr. Jo Handelsman), which is a world reference in studies regarding the use of the metagenomics technique. (AU)