MicroRNAs in the shoot apical meristem of soybean.

Plant microRNAs (miRNAs) play crucial regulatory roles in various developmental processes. In this study, we characterize the miRNA profile of the shoot apical meristem (SAM) of an important legume crop, soybean, by integrating high-throughput sequencing data with miRNA microarray analysis. A total of 8423 non-redundant sRNAs were obtained from two libraries derived from micro-dissected SAM or mature leaf tissue. Sequence analysis allowed the identification of 32 conserved miRNA families as well as 8 putative novel miRNAs. Subsequent miRNA profiling with microarrays verified the expression of the majority of these conserved and novel miRNAs. It is noteworthy that several miRNAs* were expressed at a level similar to or higher than their corresponding mature miRNAs in SAM or mature leaf, suggesting a possible biological function for the star species. In situ hybridization analysis revealed a distinct spatial localization pattern for a conserved miRNA, miR166, and its star speciessuggesting that they serve different roles in regulating leaf development. Furthermore, localization studies showed that a novel soybean miRNA, miR4422a, was nuclear-localized. This study also indicated a novel expression pattern of miR390 in soybean. Our approach identified potential key regulators and provided vital spatial information towards understanding the regulatory circuits in the SAM of soybean during shoot development.