MtROP8 is involved in root hair development and the establishment of symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti

Emerging evidence has demonstrated that ROP GTPases play important roles in symbiosis, but the molecular mechanisms on their regulation in symbiosis are largely unknown. In this study, we showed that MtROP8 is involved in the symbiotic interaction between Medicago truncatula and Sinorhizobium meliloti. Expression analyses showed that MtROP8 was down-regulated in the early infected roots, but significantly up-regulated in nodules compared to the roots. Phenotypic analysis of RNA interference (RNAi)-mediated silencing of MtROP8 revealed that knock-down of MtROP8 expression resulted in various developmental defects of root hairs, including branched hairs, short bulbous root hairs, and even root hairs with apparent swollen bases, which were caused by the modification of the distribution and the levels of reactive oxygen species (ROS). Moreover, infection events were increased in transgenic roots harboring the MtROP8 RNAi construct in response to S. meliloti inoculation, concomitant with enhanced nodulation. These results indicate that MtROP8 participates in root hair development and the establishment of the symbiotic interaction by regulating ROS production and distribution.