Rhizosphere Microbiota and Microbiome of Medicinal Plants: from Molecular Biology to Omics Approaches

The rhizosphere is a narrow region of soil that is directly influenced by roots and associated soil microorganisms. Research on rhizosphere microbes of various medicinal plants is essential for microbial ecology, applied microbiology and industrial biotechnology with regard to the sustainable utilization of Chinese medicinal resources. However, the inability of culturing most rhizosphere microorganisms (around 99%) in the laboratory obviates the research progress. In recent years, there is enormous advances in applying non-culturing techniques based on molecular biology and omics to the study of rhizosphere microbial diversity and plant-microbe interactions. DGGE, T-RFLP, ARDRA, DNA cloning and Sanger sequencing are still useful in the rhizosphere studies, while various omics tools, such as FISH, SIP, microarray, next generation sequencing (NGS), etc., evolve quickly to provide more comprehensive understanding of the rhizosphere microbiota and microbiome. Flexible applications of NGS technologies are here exemplified, e.g., amplicon sequencing, metagenomic sequencing, whole genome sequencing, and transcriptome sequencing, which address the biology and biotechnology potentials of the rhizosphere microbiome of medicinal plants. This review discusses recent findings and future challenges in the study of rhizosphere microbes, highlighting medicinal plant rhizosphere study, evolution of research methods, and innovative combinations of novel high-throughput techniques. The top-down approaches such as metagenomics and bottom-up approaches targeting individual species or strains should be integrated and combined with modeling approaches to afford a wide-ranging understanding of the microbial community as a whole.