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PNAS Papers Describe Beneficial Microbes' Use of MiRNAs to Colonize Plants, LncRNA Repression of P53

Editor's Note: Some of the articles described below are not yet available at the PNAS site but are scheduled to be posted this week.

Beneficial microbes use microRNAs to facilitate plant colonization, similar to how pathogens use the small noncoding RNAs to infect plant cells, according to a report appearing in this week's Proceedings of the National Academy of Sciences. Plant genomes encode hundreds of genes to defend against pathogens, which in turn use a variety of mechanisms to evade such defenses, including miRNAs. Despite evidence suggesting that miRNAs can be used by microbes to facilitate symbiosis with plants, the role of these small RNAs in mutualistic mycorrhizal fungal interactions is unclear. A team led by scientists from Western Sydney University used small RNA sequencing data and in situ miRNA detection to analyze miRNAs encoded by the ectomycorrhizal fungus Pisolithus microcarpus and their expression during mutualistic interaction with Eucalyptus grandis. They uncover a novel fungal miRNA that is transported into the plant's roots by the fungus to stabilize symbiosis. "These results demonstrate that beneficial fungi may regulate host gene expression through the use of miRNAs and sheds light on how beneficial microbes have evolved mechanisms to colonize plant tissues," the researchers write.

A long noncoding RNA that represses the tumor suppressor gene p53 to promote tumorigenesis is described in the Proceedings of the National Academy of Sciences this week. In addition to its well-known role as transcriptional activator that regulates the expression of genes involved in a variety of cancer-associated cellular processes, p53 is also able to repress expression of a number of protein-coding genes. Whether lncRNA repression is involved in the regulation of p53 function, however, is not known. In the study, investigators from the University of Science and Technology of China show that p53 can transcriptionally repress the expression of the lncRNA EMS, which itself can repress p53 expression. EMS exerts this suppressive effect by associating with the RNA-binding protein CPEB2, disrupting CPEB2-mediated translational control of p53 mRNA. The findings reveal a critical role for EMS in promoting tumorigenesis via p53 regulation and suggest that the lncRNA could be a therapeutic target in cancer, the study's authors write.