Role of RNA Silencing in Regulation of Gene Expression and Pathogen Defense in Plants

Abstract

U biljaka (kao i ostalih eukariota) postoji velika raznolikost molekula RNA. One imaju esencijalne i posebne uloge u stanici i organizmu. Uz kodirajuće mRNA važnu ulogu u ekspresiji gena imaju i ncRNA, u koje se ubrajaju tRNA, rRNA, lncRNA, snRNA, snoRNA, miRNA, siRNA i druge sRNA. Tema su ovog rada male molekule RNA, sRNA, čiji su najbolje istraženi predstavnici upravo neke ncRNA: snRNA, snoRNA, miRNA i siRNA. miRNA i siRNA sudjeluju u putevima RNA utišavanja, odnosno smanjuju razinu ekspresije ciljanih gena u različitim uvjetima. U biljaka se utišavanje obično provodi na posttranskripcijskoj razini putem cijepanja mRNA ciljanog gena. Za aktivnost ovih sRNA potrebni su određeni proteini, prvenstveno DCL enzimi, koji cijepaju njihove prekursore, te Argonauti, koji su glavna komponenta kompleksa RISC i cijepaju ciljane komplementarne molekule mRNA. hcsiRNA imaju posebnu ulogu u regulaciji ekspresije gena na transkripcijskoj razini, gdje se metilacijom DNA usmjerenom molekulom RNA utišavaju ciljani geni (epigenetska regulacija). Osim regulacije ekspresije endogenih gena, siRNA i RNAi pružaju biljkama važan način obrane od patogena, prvenstveno od virusa, bakterija i gljiva. U interakciji biljaka i njihovih patogena prisutni su i odgovori patogena na biljne obrambene mehanizme. I jedni i drugi mehanizmi mijenjaju se i razvijaju tijekom vremena. Otkrića iz područja RNA utišavanja našla su primjenu u razvijanju različitih metoda koje se koriste za oplemenjivanje biljaka.Plants (just like other eukaryotes) have great diversity of RNA molecules that have essential and specific functions in cell and organism. Alongside coding mRNAs important function in gene expression have ncRNAs too, which include tRNAs, rRNAs, lncRNAs, snRNAs, snoRNAs, miRNAs, siRNAs and other sRNAs. Main topic of this paper are small RNAs (sRNAs), whose best investigated representatives are some ncRNAs: snRNAs, snoRNAs, miRNAs and siRNAs. miRNAs and siRNAs act in RNA silencing pathways, i. e. they reduce expression level of targeted genes in different conditions. In plants, silencing is usually executed on posttranscriptional level by targeted gene mRNA degrading. For activity of these sRNAs are required some proteins, in first place DCL enzymes, which cleave their precursors, and Argonaute enzymes, which are principal component of RISC complex and they degrade targeted complementary mRNAs. hcsiRNAs have specific role in regulation of gene expression on transcriptional level: targeted genes are silenced by RNA-directed DNA methylation (epigenetic regulation). Beside endogenous genes expression regulation, siRNAs and RNAi provide important defense mechanisms that protect plants from pathogens, especially from viruses, bacteria and fungi. In interaction of plants and their pathogens, pathogen responses on plant defense mechanisms are also present, both are changing and developing through time. Discoveries in the field of RNA silencing found application in developing of different methods for agricultural plant breedin