Brazil is one of the world largest producers of orange and its products present a competitive and organized market generating billions of dollars every year. However, some issues impair the increase of productivity such as the occurrence of bacterial diseases. Among them, Greening (Huanglongbing/HLB), Citrus Variegated Chlorosis (CVC) and citrus canker decrease the productivity causing losses to the growers. CVC is caused by Xylella fastidiosa, a bacterium that adhere on xylem cell wall forming a biofilm, which blocks the water and nutrient flow. The most concern CVC symptom is the drastic reduction in fruits size, making them unsuitable to the concentrated juice market. The citrus canker is caused by the bacterium Xanthomonas citri pv. citri. The symptoms appear on the leaves and fruits. In highly affected plants, the citrus canker causes premature fruits drop and a consequent yield loss. These two pathogens have a gene cluster named rpf(regulator of pathogenicity factors) which is involved in the Quorum Sensing regulation. The three main genes of this cluster are rpfF,thatencodes an enzyme that synthesizes a fatty acid molecule known as Diffusible Signal Factor (DSF), this molecule is recognized by a membrane protein encoded by rpfC. The recognition of the DSF activates the transitional regulator RfpG through phosphorylation, which in turn modulate the expression of gene associated to the virulence of these two pathogens. Using a "pathogen confusion" approach, the plants overexpressing rpfF were obtained by transformation, where DSF interfered with the Quorum Sensing, decreasing the virulence of these bacteria. This approach has shown promising results on transformed sweet orange plants; however the acceptance of transgenic plants is a problem. In this way, the hypothesis of this work is that transformed rootstock could translocate DSF to a non-transgenic scion, increasing the plants tolerance to these pathogens.
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