Key molecular events involved in root exudates-mediated replanted disease of Rehmannia glutinosa

The perennial herbaceous plant, Rehmannia glutinosa Libosch, is one of traditional Chinese medicines with a long history of cultivation. However, replanted disease severely affects its yield and quality in production. In this study, a specific culture device was designed to accurately isolate the root exudates of R. glutinosa. In addition, the formation mechanism of replanted diseases mediated by root exudates was deeply studied in R. glutinosa. The results indicated that root exudates have obvious allelopathic activity, furthermore, metagenomics analysis found that the exudates were found to significantly induce the proliferation of harmful pathogenic fungal and the reduction of probiotics in rhizosphere of R. glutinosa. Further analysis found that, 8,758 genes were differentially expressed in root exudate-treated R. glutinosa plants. These genes mainly involved in critical cellular processes including immune response, hormone metabolism, signaling transduction and cell membrane transport. Of which, numerous genes were found to involve in immune response, such as PR (Pathogenesis-related protein), were highly expressed in root exudate-treated plants. Transiently overexpression experiments found that a PR1 could enhance the resistance of R. glutinosa to root exudates treatment. These results indicated that the interaction between root exudates and microbes altered the expression pattern of the genes related to immune pathway and signaling transduction mediated by it. These disordered genes finally severely affected the growth and development of R. glutinosa, and eventually formed the replanted disease. This study provides a novel approach to collect root exudates and a new data basis for revealing the molecular events occurring in replanted plants.