Regulation of LaMYB33 by miR159 during maintenance of embryogenic potential and somatic embryo maturation in Larix kaempferi (Lamb.) Carr.

During the process of subculture of embryogenic cultures, sometimes they may become non-embryogenic, which is not desirable. However, this offers an opportunity to explore the mechanisms underlying cell fate determination and the maintenance of embryogenic potential of explants during the process of somatic embryogenesis. In a previous study, differential expression of microRNAs (miRNAs) has been detected between embryogenic and non-embryogenic cultures as well as during somatic embryo maturation of Larix kaempferi (Lamb.) Carr. However, little is known about the target genes of these miRNAs during these cellular differentiation processes. In this study, full-length cDNA of the MYB homologue from L. kaempferi, LaMYB33, was cloned. Sequence analysis showed that the miR159 target sequence is present in LaMYB33. The isolation of the miRNA-guided cleavage products of LaMYB33 further suggested that this gene is regulated by miRNA. LaMYB33 transcript levels between embryogenic and non-embryogenic cultures and during the late stage of somatic embryo maturation were measured and the results showed opposite patterns in the expression of LaMYB33 and mature miR159. Based on the relationships between the expression patterns of LaMYB33 and mature miR159, we concluded that the post-transcriptional regulation of LaMYB33 by miR159 participates in the maintenance of embryogenic or non-embryogenic potential and somatic embryo maturation, providing new insights into the regulatory mechanisms of somatic embryogenesis.