Transcriptome Analysis Reveals the Biocontrol Mechanism of Endophytic Bacterium AM201, Rhodococcus sp., against Root Rot Disease of Atractylodes macrocephala.

Atractylodes macrocephala Koidz (AMK) is a perennial herb from the plant family Asteraceae (formerly Compositae). This herb is mainly distributed in mountainous wetlands in Zhejiang, Sichuan, Yunnan, and Hunan provinces of China. Its medicinal production and quality, however, are severely impacted by root rot disease. In our previous study, endophytic bacterium designated AM201 exerted a high biocontrol effect on the root rot disease of AMK. However, the molecular mechanisms underlying this effect remain unclear. In this study, the identity of strain AM201 as Rhodococcus sp. was determined through analysis of its morphology, physiological and biochemical characteristics, as well as 16S rDNA sequencing. Subsequently, we performed transcriptome sequencing and bioinformatics analysis to compare and analyze the transcriptome profiles of root tissues from two groups: AM201 (AMK seedlings inoculated with Fusarium solani [FS] and AM201) and FS (AMK seedlings inoculated with FS alone). We also conducted morphological, physiological, biochemical, and molecular identification analyses for the AM201 strain. We obtained 1,560 differentially expressed genes, including 187 upregulated genes and 1,373 downregulated genes. We screened six key genes (GOLS2, CIPK25, ABI2, egID, PG1, and pgxB) involved in the resistance of AM201 against AMK root rot disease. These genes play a critical role in reactive oxygen species (ROS) clearance, Ca signal transduction, abscisic acid signal inhibition, plant root growth, and plant cell wall defense. The strain AM201 was identified as Rhodococcus sp. based on its morphological characteristics, physiological and biochemical properties, and 16S rDNA sequencing results. The findings of this study could enable to prevent and control root rot disease in AMK and could offer theoretical guidance for the agricultural production of other medicinal herbs.