Overexpression of induces salicylic acid-dependent defense against through the regulation of its targets .

microRNAs are powerful regulators of growth, development, and stress responses in plants. The microRNA was previously found to regulate diverse processes including flower development, root development, and response to osmotic stress by controlling the patterns of expression of its target genes and . Here, we report that also modulates defense against pathogens through and . is differentially expressed in response to the bacterial pathogen , and overexpression of confers very high levels of resistance. This resistance appears to be due to suppression of auxin responses and is partially dependent upon salicylic acid signaling, and also depends upon altered stomatal behavior in these plants. Closure of stomata upon the detection of is an important aspect of the basal defense response, as it prevents bacterial cells from entering the leaf interior and causing infection. Plants overexpressing constitutively maintain small stomatal apertures, resulting in very high resistance when the pathogen is inoculated onto the leaf surface. Additionally, the systemic acquired resistance (SAR) response is severely compromised in plants overexpressing in agreement with previous work showing that the activation of SAR requires intact auxin signaling responses. This work highlights a new role for , and also emphasizes the importance of hormonal balance in short- and long-term defense and of stomata as an initial barrier to pathogen entry.