Functional Characterization of the MiR171a Promoter and Endogenous Target Mimics Identification in Lilium Pumilum DC. Fisch. During Somatic Embryogenesis

Lpu-miR171 participates in lily somatic embryogenesis by regulating SCARECROW-LIKE 6 transcription factors. However, the regulatory mechanism of lpu-miR171 remains unclear. In this study, we identified the primary transcript of lpu-miR171a and analyzed the factors influencing its expression in lily somatic embryogenesis. The full-length lpu-miR171a promoter and five 5′-deletion fragments were cloned, fused to GUS, and transferred into Arabidopsis thaliana to evaluate the promoter function. The results showed that the 1248 bp sequence located upstream of the MIR171a TSS might drive GUS expression. GUS activity was detected in only the cotyledons and radicles of transgenic A. thaliana. The GUS content was highest during seed germination and then gradually declined as growth continued. The lpu-miR171a promoter responded to light, abiotic stress, and stress-related exogenous hormone signals, including ABA, SA, and MeJA. Factors affecting lpu-miR171 family member expression were also evaluated at the posttranscriptional level, and endogenous target mimics regulating lpu-miR171a and lpu-miR171b expression were predicted using the transcriptome database. The qRT-PCR results indicated that the expression levels of lpu-miR171a and lpu-miR171b were affected by competing endogenous RNAs. This study provides a molecular basis for exploring the regulatory mechanism of lpu-miR171 during somatic embryogenesis in Lilium. For the first time, we identified and analyzed the regulatory factors of lpu-miR171 at thetranscriptional and posttranscriptional levels during lily somatic embryogenesis. The 1248 bp sequencelocated upstream of the MIR171a TSS may drive GUS expression in the cotyledons and radicles ofArabidopsis thaliana. The lpu-miR171a promoter responded to light, abiotic stress and stress-relatedexogenous hormone signals, including ABA, SA and MeJA. The expression of miR171a and miR171bis influenced by endogenous target mimics at the posttranscriptional level.