Melatonin and dopamine enhance waterlogging tolerance by modulating ROS scavenging, nitrogen uptake, and the rhizosphere microbial community in Malus hupehensis

Purpose Waterlogging poses a severe threat to the worldwide apple industry, but systematic research on the mechanisms of waterlogging resistance in apples is lacking. The roles of melatonin and dopamine in waterlogging in apples are also not understood. Methods We performed a glass container experiment to investigate the effects of exogenous melatonin and dopamine on N uptake and utilization of M. hupehensis under waterlogging stress, and the rhizosphere microbial community. Results Under waterlogging stress, melatonin and dopamine enhanced the antioxidant enzyme system and reduced reactive oxygen species (ROS) levels in plants. Importantly, melatonin and dopamine regulated the expression of genes related to N transport (NRTs, AMTs, and NLPs) and N metabolism enzymes (NR, NiR, GS, NADH-GOGAT, and Fd-GOGAT), and promoted the uptake and utilization of N in plants under waterlogging stress. Additionally, using 16S/ITS sequencing technology, we revealed for the first time the regulatory effects of melatonin and dopamine on the rhizosphere microbial community in apples under waterlogging stress. We identified the key flora (e.g., Hydrogenophaga, Flavobacterium, and Preussia) regulated by melatonin and dopamine, and effects on plant N absorption and growth, by analyzing differences in the abundance of bacteria and fungi at the order and genus levels, and identified correlations with plant growth and development. Conclusions Our results show that melatonin and dopamine effectively reduce ROS, promote N uptake and utilization, and regulate specific microbial communities, thus alleviating the inhibitory effects of waterlogging stress on the growth and development of apple plants.

Automated summary

This study investigated the effects of melatonin and dopamine on the waterlogging resistance mechanisms in apple plants and the microbial community in the rhizosphere under waterlogging stress. The results showed that melatonin and dopamine enhanced antioxidant enzyme activity, promoted nitrogen uptake and utilization, and regulated specific microbial communities, alleviating the inhibitory effects of waterlogging stress on apple plant growth and development.