Science publishes CNPEM research on a novel strategy used by the bacterium that causes citrus canker

The study paves the way for controlling a disease that affects crops worldwide, causing billions of dollars in losses

Researchers from Brazilian Center for Research in Energy and Materials (CNPEM), in Campinas (SP), participated in a groundbreaking discovery published in the prestigious journal Science that reveals a sophisticated attack mechanism of the bacterium that causes citrus canker, Xanthomonas citri. This study is of great relevance to the global citrus industry, since citrus canker has been responsible for eradication operations that have removed approximately 16 million trees, mainly orange and lemon trees, and have cost producing countries billions of dollars.

The study paves the way for controlling a disease that affects crops worldwide, causing billions of dollars in losses

The results pave the way for developing more effective control strategies. Among the possibilities are the creation of citrus fruits with genetically modified versions that cannot be activated by the bacteria, and the identification of molecules capable of interrupting the release or consumption of sugars inside the plant used to feed and proliferate these bacteria.

The research is led by the University of Tübingen, Germany, which invited CNPEM to participate because of its excellence in studies on carbohydrate metabolism developed over the last 15 years, making it a world reference. In Brazil, the study was carried out with support from the Ministry of Science, Technology and Innovation (MCTI) and the São Paulo Research Foundation (FAPESP).

The study identified that the pathogen “hacks” the plant, activating a gene associated with fruit ripening, CsLOB1, to release sugars from the cell walls and use them as fuel for its own multiplication.

CNPEM, through researchers from the Brazilian Biorenewables National Laboratory (LNBR) and funding from Fapesp, led key parts of the study, including genomic and biochemical analyses that allowed for the identification of enzymes involved in cell wall degradation and the use of sugars by the bacteria. The laboratory also contributed to the interpretation of the metabolic network activated by Xanthomonas, detailing the energetic and functional impact of this exploration of the plant.

“The discovery of this mechanism has the potential to generate an economic impact worldwide and, in particular, in Brazil, which is the world’s largest producer and exporter of orange juice, representing more than 75% of all global orange juice trade. And this discovery is not limited to citrus farming, as the process of controlling fruit ripening is conserved in other plants, and could serve as a tool for the entire fruit growing sector”, says Mario Murakami, Director of LNBR and coordinator of this research at CNPEM.

Mechanism

Research shows that the bacterium injects a protein called PthA4 into the plant, which is capable of “switching on” the CsLOB1 gene. When this occurs outside the natural context of the fruit, the plant begins to produce enzymes that degrade its own cell wall, releasing carbohydrates such as glucose, fructose, and xylose. This biochemical broth feeds Xanthomonas, accelerating its proliferation and worsening the disease. The study also reveals that the bacteria simultaneously utilize two secretion systems, one to disable the plant’s defenses and another to release degrading enzymes, in a synergy that intensifies the infection.

In addition to elucidating this molecular mechanism, the scientists demonstrated that the CsLOB1 gene, exploited by the bacterium, is naturally active in fruit ripening, which explains why Xanthomonas takes advantage of a process already existing in plant metabolism. Evidence was also found that similar mechanisms operate in tomato plants, showing that this type of molecular control can be conserved in other species.