The pathway holds enormous potential of being used to produce new fungicides or new resistant rice plants to hold this pathogen at bay. However, rice blast fungus is able to quickly evolve new tricks to tackle rice plants, apparently because the fungus and the grain developed side by side over centuries, according to genetic experts. To overcome the fungus' wiles, researchers need to know more than just the one pathway.
"We want to know how the plant and the fungus talk," Xu said. "We need to know the signal, or ligand, the rice plant gives to the receptor on the fungus that allows the penetration process to proceed. We need to understand the whole communication among all the genes in the rice blast penetration pathway before we can design a rice plant that resists this fungus."
Researchers already have some additional pieces of the puzzle gleaned from sequencing the rice blast genome. They learned that the pathogen has a unique family of proteins that acts as feelers to tell the fungus when it has a good host plant and how the plant might fight a fungal invasion. These feelers are called G-protein-coupled receptors (GPCR). In humans, GPCRs are found on the tongue and in the nose and are part of what makes foods taste different.
The scientists discovered that rice blast fungus has more than 40 GPCRs that probably are regulating the signals at the beginning of the penetration pathway.
"We are working on the basic infection process," Xu said. "We want to know what genetic mechanisms regulate this process, how the fungus spores recognize the plant surface, and how they know to penetrate it."
Once the fungus enters the rice leaf cells, the infected cells attempt to defend the plant by dying. This means death for young plants, while in older plants, rice grain is