Identification and functional characterization of soybean root hair micro RNA s expressed in response to B radyrhizobium japonicum infection

Summary Three soybean [ Glycine max (L) Merr.] small RNA libraries were generated and sequenced using the Illumina platform to examine the role of mi RNA s during soybean nodulation. The small RNA libraries were derived from root hairs inoculated with B radyrhizobium japonicum (In_ RH ) or mock‐inoculated with water (Un_ RH ), as well as from the comparable inoculated stripped root samples (i.e. inoculated roots with the root hairs removed). Sequencing of these libraries identified a total of 114 mi RNA s, including 22 novel mi RNA s. A comparison of mi RNA abundance among the 114 mi RNA s identified 66 mi RNA s that were differentially expressed between root hairs and stripped roots, and 48 mi RNA s that were differentially regulated in infected root hairs in response to B . japonicum when compared to uninfected root hairs ( P  ≤ 0.05). A parallel analysis of RNA ends ( PARE ) library was constructed and sequenced to reveal a total of 405 soybean mi RNA targets, with most predicted to encode transcription factors or proteins involved in protein modification, protein degradation and hormone pathways. The roles of gma‐miR4416 and gma‐miR2606b during nodulation were further analysed. Ectopic expression of these two mi RNA s in soybean roots resulted in significant changes in nodule numbers. mi RNA target information suggested that gma‐miR2606b regulates a Mannosyl‐oligosaccharide 1, 2‐alpha‐mannosidase gene, while gma‐miR4416 regulates the expression of a rhizobium‐induced peroxidase 1 ( RIP 1 )‐like peroxidase gene, Gm RIP 1 , during nodulation.