Biogenesis of a 22-nt microRNA in Phaseoleae species by precursor-programmed uridylation

Proc Natl Acad Sci U S A. 2018 Jul 31;115(31):8037-8042. doi: 10.1073/pnas.1807403115. Epub 2018 Jul 16.


Phased, secondary siRNAs (phasiRNAs) represent a class of small RNAs in plants generated via distinct biogenesis pathways, predominantly dependent on the activity of 22-nt miRNAs. Most 22-nt miRNAs are processed by DCL1 from miRNA precursors containing an asymmetric bulge, yielding a 22/21-nt miRNA/miRNA* duplex. Here we show that miR1510, a soybean miRNA capable of triggering phasiRNA production from numerous nucleotide-binding leucine-rich repeat (NB-LRRs), previously described as 21 nt in its mature form, primarily accumulates as a 22-nt isoform via monouridylation. We demonstrate that, in Arabidopsis, this uridylation is performed by HESO1. Biochemical experiments showed that the 3' terminus of miR1510 is only partially 2'-O-methylated because of the terminal mispairing in the miR1510/miR1510* duplex that inhibits HEN1 activity in soybean. miR1510 emerged in the Phaseoleae ∼41-42 million years ago with a conserved precursor structure yielding a 22-nt monouridylated form, yet a variant in mung bean is processed directly in a 22-nt mature form. This analysis of miR1510 yields two observations: (i) plants can utilize postprocessing modification to generate abundant 22-nt miRNA isoforms to more efficiently regulate target mRNA abundances; and (ii) comparative analysis demonstrates an example of selective optimization of precursor processing of a young plant miRNA.

Keywords: disease resistance; microRNA; plant evolution; soybean; uridylation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • MicroRNAs / biosynthesis*
  • RNA Processing, Post-Transcriptional*
  • Soybeans / genetics*
  • Uridine / metabolism*
  • Uridine Monophosphate / metabolism


  • MicroRNAs
  • Uridine Monophosphate
  • Uridine