Coordination of microbe-host homeostasis via a crosstalk with plant innate immunity (Research Square)

In nature, roots are colonized by commensal bacteria that do not seem to influence host traits. Recently, studies showed some commensals can suppress plant immune responses when inoculated to plants alone. However, how such commensal activities are coordinated in the community context is poorly understood. Ma, Niu et al. took a bottom-up approach to explore immune-modulating activities of various commensals and their interactions. The authors found that taxonomically diverse commensal strains (62 out of 151 strains) can interfere with root growth inhibition (RGI) induced by flg22 peptide, a microbe-derived immune elicitor. They then composed 5-member synthetic communities with suppressive or non-suppressive strains (suppressive/non-suppressive SynComs). They found that suppression of flg22-triggered RGI is, in some cases, associated with the ability of commensal strains to modify or degrade flg22 peptide. Flg22 treatment altered community structure of non-suppressive SynComs, but not suppressive SynComs, implying that flg22-induced immunity influences root microbiota establishment. Interestingly, mixtures of suppressive and non-suppressive SynComns was not affected by flg22 treatment, suggesting that RGI-suppression is the dominant trait in plant-associated bacterial communities and is thus easily overlooked in previous studies. Transcriptome analyses revealed a subset of known defense-related genes upregulated by a non-suppressive SynCom but downregulated by a suppressive SynCom. Furthermore, pre-colonization by non-suppressive SynComs protected plants from opportunistic pathogens, whereas suppressive SynComs did not. Together, the authors propose a model in which a balance between commensals with contrasting immune-modulating activities buffers plant resistance against pathogens and defense-associated plant growth reduction, eventually leading to microbe-host homeostasis. (Summary by Tatsuya Nobori @nobolly) Research Square 10.21203/