DISCOVERY MAY HELP KAURI
Researchers at the University of California, Riverside have made a discovery that could prove important in the fight against PTA, the pathogen known as Kauri Dieback that is killing our great tree. The scientists identified a fundamental microbiological process that could be at the heart of the fungal nasty, Phytophthora taxis agathis that is the cause of the current Kauri Dieback epidemic.
Kauri was resistant to phytophthora, of which there are thousands of species, so the current attack on these trees has taken local scientists and foresters by surprise. However the discovery of the method phytophthora uses to suppress a plant’s immune system may help fight the dieback problem.
Phytophthora attacks plants through cytoplasm secreting mechanisms known as haustoria. Their secretions use a motif, the molecular structure of a substance called an effector that the plant identifies as friendly, to invade the plant’s basic intercellular functions at a molecular level. However, scientists have so far failed to identify how this happens once the infection is inside the plant.
Now it appears that the motif used by phytophthora, mostly that of an effector known as RxLR, engages directly with proteins in the plant know as interacting proteins. These are the means by which plants control their supply and utilisation of RNA, which they suppress as their main means of defence against viral activity.
It appears that RxLR closes down the suppression function of the interacting proteins, PSR1 and PSR2, by having a direct influence on another protein. This nuclear protein containing the aspartate-glutamate-alanine-histidine-box RNA helicase domain in the plant is known as PSR1-interacting protein 1 (PINP1), and it may hold the key to kauri survival. As it is required for the accumulation of small RNAs and to be important to miRNA and siRNA biogenesis and processing, it appears to be a critical part of phytophthora’s attack mechanism.
The full paper,
Qiao Y, Shi J, Zhai Y, Hou Y, and Ma W, : Phytophthora effector targets a novel component of small RNA pathway in plants to promote infection,
Was published in The Proceedings of the National Academy of Science, April 20 2015.