Telling TALEs of rice blight
Some bacteria use TALE proteins to hijack plant defenses and cause disease.
Around the world, bacterial infections reduce the yields of many important crops like rice, tomatoes, peppers and citrus fruits. Xanthomonas is a particularly widespread genus of bacteria; it consists of almost 30 species that cause diseases in more than 400 plant hosts, including bacterial blight and bacterial streak in rice plants.
Plants do have an immune system that is able to detect invading microbes and trigger a defensive response against them; however, many disease-causing bacteria have evolved ways to avoid or counteract this response. For example, at least five Xanthomonas species use proteins called transcription activator-like effectors (or TALEs for short) to infect their host plants. The bacterial proteins are essentially injected into the plant’s cells where they activate specific plant genes that make the host more susceptible to infection. Like other organisms, plants use proteins called transcription factors to switch genes on or off. However, it was not clear if the TALEs hijack the plant’s transcriptional machinery to activate these “susceptibility genes” or if they activate the genes via some other means.
Now, Meng Yuan and colleagues show that TALE-carrying bacteria do make use of at least one of rice’s own transcription factors to cause bacterial blight and bacterial streak. The transcription factor in question is rice’s version of a general transcription factor, called TFIIAγ, which is essential for gene activation in plants, animals and fungi. Yuan and colleagues also identify the region of the TALE that binds to the transcription factor, and show that rice plants with lower levels of the transcription factor are protected against bacterial blight and bacterial streak.
Uncovering how disease-causing Xanthomonas bacteria use TALEs to infect plants will hopefully help researchers to develop crop plants that are more resistant to these harmful bacteria. Further work is now needed to see if the gene that encodes TFIIAγ in crop plants can be edited to achieve this goal, or whether genes encoding resistant variants of the protein already exist in other plant species.
To find out more
Read the eLife research paper on which this eLife digest is based: “A host basal transcription factor is a key component for infection of rice by TALE-carrying bacteria” (July 29, 2016).