Unravelling the effect of the transcription factor DOF1147 and of auxin on cell division and endoreduplication in developing seeds of the model legume Medicago truncatula

Due to high protein contents, legume seeds provide an important source for human and animal nutrition and play therefore a crucial role in research regarding the improvement of seed quality. Previous studies have demonstrated that reserve production and accumulation in legume seeds is transcriptionally regulated, in which the transcription factor DOF1147 is involved. In addition, auxin is known to play a significant role in modelling the transition from mitotic cycles to endocycles in Medicago truncatula developing seeds by favoring sustained cell divisions while prolonging endoreduplication. The intent of this study was to examine the effect of the transcription factor DOF1147 and of auxin on cell division and endoreduplication in immature seeds of Medicago truncatula. Therefore, the study’s focus rests on the transition from the embryo cell division to seed filling phase, and it compares a wild-type genotype with a DOF1147-overexpressing transformant. Thus, seeds were harvested at 8, 10, 12, 14 and 16 DAP (days after pollination) and cultured in vitro on media either without auxin or supplemented with indole-3-butyric acid (IBA) or naphthaleneaceticacid (NAA) at 1 mg/l. The in vitro seed development was analyzed by flow cytometry and by the kinetics of seed fresh weight and surface area, with all parameters determined every two days from the start of in vitro culture. The results showed that auxin causes an increase in seed weight and size, with NAA having a stronger effect than IBA. Interestingly, the transformant seeds exhibited a stronger reaction as compared to wild-type seeds. In addition, endoreduplication occurred earlier and for a longer period of time in the seeds of the DOF1147-transformant with NAA having again the greatest effect. The results of this study confirm previous observations on the participation of auxin in seed development and unveil new information about the gene DOF1147 and its activity during the filling stage of legume seed development.