Effect of N-acetyl-L-cysteine (NAC) applied by fertigation in reversing symptoms of Variegated Citrus Chlorosis (CVC) and colonization of X. fastidiosa in sweet orange (Citrus sinensis)

Abstract

Citrus production in Brazil is one of the most important activities agribusiness. The citrus agribusiness has contributed in successive trade surplus in Brazil generating foreign exchange and jobs. However, the productivity of Brazilian citrus is very low, which is associated with the simultaneous expansion of pests and diseases, with significant reflected in production costs. The major biotic factors limiting citrus include diseases such as citrus variegated chlorosis (CVC) caused by the bacterium Xylella fastidiosa. The X. fastidiosa insect vector is injected directly into the vessels of the xylem, where it adheres and colonizes. The whole process leads to the formation of biofilms and it is considered the main mechanism of pathogenicity of this microorganism. The biofilm formation is composed of different stages starting with the accession in biotic or abiotic surface. One of the main characteristics of this bacterium, which reflects its ability to trigger the symptoms of the disease, is the expression of adhesins protein capable of promote efficient adhesion on the surface of the host. For bacterial pathogens of humans, a form of control of these bacteria has been destroying the biofilm attached on the surface of the host. This is used for analogue cysteine, N-acetyl-L-cysteine (NAC). NAC is an antioxidant molecule that breaks the disulfide bridges adhesins by competition with cysteine, due to the use of NAC instead cysteine. The objective of this work is to evaluate, from studies conducted by our research group (showing the effect of NAC in biofilm formation of X. fastidiosa in infected plants) the effect of this compound in a condition closer to field conditions, where infected plants are maintained in soil treated with NAC for fertigation. Also due to the fact that the mechanism of pathogenicity of this bacterium to be associated with their level of activity and colonization in the xylem vessels, we intend to understand whether the NAC actually interferes in biofilm formation, as proposed by our group, and / or ability to move this bacteria in the xylem, since both the type IV fimbrial protein (involved in systemic movement of bacteria) and fimbrial type I and afimbrial protein (involved in cell-cell adhesion on the surface) can have cysteine in their structure and thus susceptible to the action of NAC.