Nature reports the new discovery of plant miRNA, PRI miRNA

The maturation of miRNA generally needs several steps: the first step, miRNA gene transcription produces PRI miRNA; the second step, PRI miRNA is sheared by Drosha enzyme complex to produce pre miRNA; the third step, pre miRNA enters the cytoplasm from the nucleus and is sheared by Dicer enzyme complex to produce mature miRNA It is generally believed that only mature miRNA can play a regulatory role, while PRI miRNA and pre miRNA play a regulatory role directly However, in nature published on April 2, researchers from the University of Toulouse in France reported the latest research results on PRI miRNA in their latest paper They found that PRI miRNA can translate and produce some oligopeptides, and promote the transcription of miRNA gene Since PRI miRNA is produced by transcription of RNA Pol II, the researchers hypothesized that PRI miRNA has protein coding ability In order to test this hypothesis, researchers chose the model plant Medicago truncatula to explore its mir171 family Previously, it has been found that mir171b can regulate the development of lateral roots The researchers first identified the full length of 284 kinds of pri mir171b through race experiments The results showed that there were many SNPs in the promoter region and 3 'region of PRI miRNA, but the corresponding pre miRNA, mature miRNA and 5' region in pri miRNA were very conservative The researchers identified two open reading frames in the 5 'region Frame, ORF), corresponding to a 20 amino acid and a 5 amino acid short peptide   The 5 'terminal sequence of pri-mir171b confirmed by race contains two ORFs, and the underscore indicates the gus insertion site In order to verify the status of the two ORF translation starting sites, the researchers recombined the translation starting sites corresponding to the β - glucuronidase reporter gene Gus and PRI mir171b, and confirmed that only the ORF corresponding to 20 amino acids could translate and produce polypeptides in plants For this predicted peptide, the researchers designed a specific antibody, and confirmed the existence of this peptide by immunofluorescence test The researchers named this peptide mipep171b In order to explore the function of mipep171b in the development of mir171b and its lateral roots, the wild and mutant alfalfa pri-mir171b was introduced into tobacco leaf cells The results showed that wild type mipep171b could increase the expression of mir171b and reduce the rate of lateral root formation Pri-mir171b with ORF and translation start site mutations produced less mir171b, and pri-mir171b under normal conditions Even if there are many mutations in ORF, if the amino acid sequence is not changed, it will still have a regulatory effect on mir171b, which shows that pri mir171b does play a role by producing protein through ORF, not in the form of RNA Since then, the researchers have verified ten kinds of PRI miRNAs in a variety of Tribulus Medicago and Arabidopsis These PRI miRNAs contain at least one ORF, which can translate and produce mipep, and further promote the production of mature miRNAs The researchers believe that these evidences are enough to show that it is a common phenomenon that PRI miRNA translation produces short peptides and further promotes the corresponding mature miRNA expression in plants For the mechanism of mipep promoting miRNA expression, the researchers first detected the change of pri-mipep165a expression after two hours' treatment of Arabidopsis mipep165a seedlings As a result, pri-mipep165a was up-regulated when cells or mutant RNA pol were treated with cordycepin, an RNA synthesis inhibitor At II, mipep no longer promoted PRI miRNA expression, which indicated that mipep could stabilize PRI miRNA or promote PRI miRNA transcription Mipep165a promotes the up regulation of mir165a in Arabidopsis root endothelial cells These functions of mipep have caused several problems, including how the translation process of PRI miRNA in the cytoplasm coordinates with the ripening process of PRI miRNA in the nucleus, how mipep interacts with the transcription system, and how the molecular mechanism of their regulatory functions actually works Researchers will continue to study these problems Related literature: primary scripts of microRNAs encode regulatory peptides