Isolation and Characterization of Sugarcane Genes Involved in the Association with Endophytic Diazotrophs

Very little is known about the role of the plant in the association between sugarcane and the endophytic diazotrophs A. diazotrophicus and Herbaspirillum spp. The differences of the contribution of BNF in distinct sugarcane genotypes indicate that plant genetic factors are contributing to the efficiency of the process. The susceptibility of some cultivars to H. rubrisubalbicans strengthen the hypothesis that the mechanism of plant/bacteria interaction in this association is dependent on the plant genetic information. In order to elucidate the role of the plant in this interaction, plant genes induced by the association with the bacteria are being isolated by the technique of ddRT-PCR. Plants microorganism-free, obtained by in vitro meristem culture, are being inoculated only with A. diazotrophicus, only with Herbaspirillum spp., with a Herbaspirillum mutant that does not fix nitrogen and with a mixture of A. diazotrophicus and Herbaspirillum spp. Among the differentially expressed fragments isolated, two are being further characterized. One of the genes, called MisA2, is expressed only in plants infected with the mixture of bacteria. The deduced amino acid sequence of a partial cDNA isolated does not show significant homology with any described protein of the DataBank. Nevertheless, it has some features which could indicate a possible function. The protein is proline-rich, a feature of some nodulins which are suggested to be located in the cell wall formed inside the infection thread. The other gene, called AcA5, is induced in plants infected either with A. diazotrophicus or Herbaspirillum spp., or with the mixture of bacteria, but not with the mutant. The sugarcane gene is homologous to an endossomal membrane protein of yeast. The function of the isolated genes in the interaction are still unknown.