Identification of microRNAs involved in pathogen-associated molecular pattern-triggered plant innate immunity.

Pathogen-associated molecular patterns (PAMPs) trigger plant defenses when perceived by surface-localized immune receptors. PAMP-triggered immunity (PTI) plays a vital role in the resistance of plants to numerous potential pathogens. MicroRNA (miRNA) biogenesis is known to be important for PTI, but miRNA species involved in this process have not been fully explored. Here we show that the Arabidopsis (Arabidopsis thaliana) miRNA effector protein, Argonaute1 (AGO1), is required for a number of PTI responses including PAMP-induced callose deposition, gene expression, and seedling growth inhibition. Deep sequencing of AGO1-bound small RNAs led to the identification of a number of miRNAs that are up- or down-regulated by flg22, a well-studied PAMP. Overexpression of selected miRNAs in stable transgenic plants demonstrated that miR160a positively regulate PAMP-induced callose deposition, whereas miR398b and miR773 negatively regulate PAMP-induced callose deposition and disease resistance to bacteria, suggesting a complexity of the miRNA regulation in plant innate immunity.