Alterations in the transcriptome of soybean in response to enhanced somatic embryogenesis promoted by orthologs of AGAMOUS-Like15 and AGAMOUS-Like18

Somatic embryogenesis (SE) is a poorly understood process during which competent cells respond to inducing conditions, allowing the development of somatic embryos. It is important for the regeneration of transgenic plants, including for soybean (Glycine max). We report here that constitutive expression of soybean orthologs of the Arabidopsis (Arabidopsis thaliana) MADS box genes AGAMOUS-Like15 (GmAGL15) and GmAGL18 increased embryogenic competence of explants from these transgenic soybean plants. To understand how GmAGL15 promotes SE, expression studies were performed. Particular genes of interest involved in embryogenesis (ABSCISIC ACID-INSENSITIVE3 and FUSCA3) were found to be directly up-regulated by GmAGL15 by using a combination of quantitative reverse transcription-polymerase chain reaction and chromatin immunoprecipitation. To look more broadly at changes in gene expression in response to GmAGL15, we assessed the transcriptome using the Affymetrix Soybean Genome Array. Interestingly, the gene expression profile of 35Spro:GmAGL15 explants (0 d in culture) was found to resemble nontransgenic tissue that had been induced for SE by being placed on induction medium for 3 d, possibly explaining the more rapid SE development observed on 35Spro:GmAGL15 tissue. In particular, transcripts from genes related to the stress response showed increased transcript accumulation in explants from 35Spro:GmAGL15 tissue. These same genes also showed increased transcript accumulation in response to culturing nontransgenic soybean explants on the medium used to induce SE. Overexpression of GmAGL15 may enhance SE by making the tissue more competent to respond to 2,4-dichlorophenoxyacetic acid induction by differential regulation of genes such as those involved in the stress response, resulting in more rapid and prolific SE.