Melatonin induces endoreduplication through oxidative DNA damage triggering lateral root formation in onions

This study reports the potential ability of melatonin (Mel) to induce endoreduplication, which may have connections with lateral root formation. Mel induces the lateral root formation in onions in a dose-dependent manner with the highest root forming potential at 50 µM Mel (Mel_2). ROS generation in this dose was significantly higher than the control and a low-dose (5 µM) Mel group (Mel_1), where no lateral roots were observed. Co-treatment of ascorbic acid (AsA) with Mel in the Mel_2 + AsA group can effectively scavenge the Mel_2 induced ROS, resulting in a reduced number of lateral roots in this co-treatment group. These results indicate the connections between the ROS level and the lateral root formation. An increase in DNA content was also observed in the Mel_2 group consistent with the level of ROS-induced DNA damage, suggesting the possible link between ROS-induced DNA damage, endoreduplication, and lateral root formation. The results of gene expression analysis also support the said linkage, where melatonin-induced ROS and DNA damage could initiate the endoreduplication cycle in a dose-dependent manner. The IAA (Indole acetic acid) analysis indicates that IAA accumulation, in the zone of differentiation due to auxin bio-synthesis, triggers lateral root formation in this region in corroboration with endoreduplication and ROS.