sly-miR408b Targets a Plastocyanin-Like Protein to Regulate Mycorrhizal Symbiosis in Tomato.

Symbiosis between arbuscular mycorrhizal fungi and plants plays a crucial role in nutrient acquisition and stress resistance for terrestrial plants. microRNAs have been reported to participate in the regulation of mycorrhizal symbiosis by controlling the expression of their target genes. Herein, we found that sly-miR408b was significantly downregulated in response to mycorrhizal colonisation. Overexpression of sly-miR408b compromised mycorrhizal colonisation by Rhizophagus irregularis in tomato (Solanum lycopersicum) roots. A basic blue protein gene (SlBBP) was then identified as the new target gene of miR408b in tomato. The expression of membrane-located SlBBP was induced in a copper-dependent manner. Importantly, the loss function of SlBBP decreased the root mycorrhizal colonisation. Overexpression of SlBBP decreased SOD activity, which may interfere with the process of scavenging excessive reactive oxygen species (ROS). Mutation of RBOH1, which encodes ROS-producing enzymes NADPH oxidases, obviously reduced the arbuscule abundance in the mutant roots. Overall, our results provide evidence that sly-miR408b and its target gene SlBBP regulate mycorrhizal symbiosis in tomato through mediating ROS production.