The miR396-GRF Regulatory Module Controls the Embryogenic Response in Arabidopsis via an Auxin-Related Pathway

In plants, microRNAs have been indicated to control various developmental processes, including somatic embryogenesis (SE), which is triggered in the in vitro cultured somatic cells of plants. Although a transcriptomic analysis has indicated that numerous MIRNAs are differentially expressed in the SE of different plants, the role of specific miRNAs in the embryogenic reprogramming of the somatic cell transcriptome is still poorly understood. In this study, we focused on performing a functional analysis of miR396 in SE given that the transcripts of MIR396 genes and the mature molecules of miR396 were found to be increased during an SE culture of Arabidopsis [1]. In terms of miR396 in embryogenic induction, we observed the SE-associated expression pattern of MIR396b in explants of the β-glucuronidase (GUS) reporter line. In order to gain insight into the miR396-controlled mechanism that is involved in SE induction, the embryogenic response of mir396 mutants and the 35S:MIR396b overexpressor line to media with different 2,4-Dichlorophenoxyacetic acid (2,4-D) concentrations was evaluated. The results suggested that miR396 might contribute to SE induction by controlling the sensitivity of tissues to auxin treatment. Within the targets of miR396 that are associated with SE induction, we identified genes encoding the GROWTH-REGULATING FACTOR (GRF) transcription factors, including GRF1, GRF4, GRF7, GRF8, and GRF9. Moreover, the study suggested a regulatory relationship between miR396, GRF, and the PLETHORA (PLT1 and PLT2) genes during SE induction. A complex regulatory relationship within the miR396-GRF1/4/8/9-PLT1/2 module that involves the negative and positive control of GRFs and PLT (respectively) by miR396 might be assumed.