miR171 and its target gene SCL6 contribute to embryogenic callus induction and torpedo-shaped embryo formation during somatic embryogenesis in two lily species

Somatic embryogenesis (SE) is the capacity of plant somatic cells to form embryos through a process resembling zygotic embryogenesis. This process is used as a model system to study zygotic embryo development. miRNAs play a crucial role in regulating the occurrence and development of plant SE. In our previous study, miR171 showed differential expression in the various developmental stages of SE in Lilium pumilum DC. Fisch. and Lilium davidii var. unicolor. However, little is known about the regulatory mechanism of miR171 and its target genes during Lilium SE. Here, the mature sequences of lpu-miR171a, lpu-miR171b, lda-miR171a and lda-miR171c were cloned using stem-loop RT-PCR. Furthermore, SCL6 transcription factors were verified to be the targets of miR171 using RLM-RACE. In addition, the full-length open reading frames for three target genes were cloned. The qRT-PCR results indicate that expression profiles differ among members of the miR171 family. lpu-miR171a expresses at high levels in the embryonic callus stage, while lda-miR171a, lda-miR171c and lpu-miR171b have the highest expression levels in the torpedo-shaped embryo stage. The expression levels of targets were negatively correlated with those of lpu-miR171a and lpu-miR171b; however, the levels of lda-miR171a and lda-miR171c were positively correlated with those of their target genes. The developmental stage-specific expression profiles of miR171 and SCL6 genes during SE implied that they have different regulatory functions during lily SE. According to the relationships between the expression files of miR171 and its target, the miR171 family functions in the regulation of SE, especially in the development of torpedo-shaped embryos.