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

Abstract

AbstractMelatonin (Mel) can regulate lateral root formation, but the underlying molecular mechanisms of Mel-induced lateral root formation are indistinct. This study first time reports the potential ability of melatonin to induce endoreduplication, which in turn could play important roles in developmental reprogramming in plants towards lateral root formation. Pursuant to the results, Mel induces the lateral root formation in onions in a dose-dependent manner with the highest root forming potential in the high concentration (50 µM) of Mel. In consistent with the lateral root formation, the ROS generation in this dose was significantly higher than the control and a low dose (5 µM Mel, Mel_1) group. Co-treatment of ascorbic acid (AsA) with Mel in Mel_2 + AsA group can effectively scavenge the Mel_2 induced ROS, which results in a reduced number of lateral root formation in the co-treatment group. The higher levels of H2O2and superoxide in Mel_2 further strengthen the previous report on the role of ROS in 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 that ROS can induce lateral root formation through oxidative DNA-damage stress and resulting endoreduplication. The results of gene expression analysis through qRT-PCR provide supporting evidence that melatonin, in a dose-dependent manner, can arrest cell-cycle, initiating the endoreduplication cycle in response to oxidative DNA-damage. Observed low level of IAA in primary root tip indicates the DNA-damage and cytokinin-dependent inhibition of auxin polar transport, causing localised IAA accumulation in the zone of differentiation due to auxin bio-synthesis, which in turn triggers lateral root formation in this region in corroboration with endoreduplication and ROS.