Asterisks indicate significant differences (*P< 0.05 and **P< Pectolinarin 0.01). assay showed that this expression of some target genes was negatively correlated with the expression ofmiRNAs. Moreover, transgenic rice plants overexpressingmiR160aandmiR398bdisplayed enhanced resistance toM. oryzae, as exhibited by decreased fungal growth, increased hydrogen peroxide accumulation at the contamination site, and up-regulated expression of defense-related genes. Taken together, our data indicate thatmiRNAs are involved in rice immunity againstM. oryzaeand that overexpression ofmiR160aormiR398bcan enhance rice resistance to the disease. In plant-pathogen coevolution, plants mount a two-layered immune system to protect themselves from being damaged by pathogenic microbes. In the first layer of immunity, plants detect conserved molecular features of microbes, termed pathogen-associated molecular patterns (PAMPs), to trigger immunity (pathogen-associated molecular pattern-triggered immunity [PTI]) that is efficient to prevent a large number of potential pathogenic microbes from invasion (Zipfel and Felix, 2005). Successful pathogens deliver effectors into herb cells to suppressPTIand establish parasitism (Boller and He, 2009;Dou and Zhou, 2012). In turn, the second layer of herb immunity, called effector-triggered immunity (ETI), is initiated upon the recognition of effectors by the cognate intracellular immune receptors, such as nucleotide-binding site leucine-rich repeat (NBS-LRR)-type proteins.ETIis usually concomitant with the hypersensitive response, a programmed cell death at the contamination site to inhibit the diffusion of the invading pathogen (Alfano and Collmer, 2004;Chisholm et al., 2006;Jones and Dangl, 2006). In plant-fungus interactions,PTIandETIequip herb preinvasive and postinvasive resistance, respectively. Increasing evidence demonstrates that small RNAs are involved in bothPTIandETIsignaling and act as key fine-tuning regulators (Padmanabhan et al., 2009;Katiyar-Agarwal and Jin, 2010). Small RNAs are short noncoding RNAs that guideline gene silencing either by regulating chromatin methyl modification or by mRNA degradation and translational repression (Baulcombe, 2004;Seo et al., 2013). They are classified into microRNAs (miRNAs) and small interfering RNAs (siRNAs) based on their biogenesis and origin. BothmiRNAs andsiRNAsare Pectolinarin involved in the regulation of diverse biological processes, including development and responses to biotic and abiotic stresses (Katiyar-Agarwal and Jin, 2010;Chen, 2012;Khraiwesh et al., 2012). In Arabidopsis (Arabidopsis thaliana), a set ofmiRNAs were identified to be responsive to thePAMPmolecule flg22 or to the infection of nonpathogenic strainPseudomonas syringaeDC3000 with mutation in hypersensitive response and pathogenicity conserved C (hrcC;Fahlgren et al., 2007;Li et al., 2010a;Zhang et al., 2011). The first identifiedPTI-related small RNA ismiR393, which can be induced by thePAMPmolecule flg22 and positively contributes toPTIby suppressing auxin signaling by silencing auxin receptors (Navarro et al., 2006). In addition,miR160a,miR398b, andmiR773are involved ITGA8 in the regulation of callose deposition and, thus, act inPTIsignaling (Li et al., 2010a). SomemiRNAs also exhibit differential induced responses to the contamination of pathogenic and avirulent strains ofP. syringaeDC3000 and, thus, are involved inETIsignaling (Zhang et al., 2011). More recently, somemiRNAs were found to guide the cleavage ofNBS-LRR-type disease resistance (R) genes in Solanaceae and Leguminosae species, indicating that thesemiRNAs are key regulators inETI(Zhai et al., 2011;Li et al., 2012;Shivaprasad et al., 2012). The study ofmiRNAs in rice (Oryza sativa) has progressed from computational prediction to experimental identification and Pectolinarin functional characterization (Reinhart et al., 2002;Rhoades et al., 2002;Jones-Rhoades and Bartel, 2004;Liu et al., 2005). The first set of ricemiRNAs experimentally identified was reported in 2004 (Wang et al., 2004). Later, moremiRNAs, either conservative or novel in rice, were identified from rice shoot, root, inflorescence, panicle, calli, developing grains, and immature seeds (Liu et al., 2005;Sunkar et al., 2005;Luo et al., 2006;Zhu et al., 2008;Xue et al., 2009). By exposing rice seedlings to drought Pectolinarin or salt stress and through high-throughput sequencing,Sunkar et al. (2008)identified 23 newmiRNAs and 40 candidates. By subjecting them to drought stress from tillering to inflorescence formation stages, 30miRNAs were identified to be differentially expressed under drought conditions (Zhou et al., 2010a). By comparing samples from normal conditions and exposure to oxidative stress,Li et al. (2011)identified sevenmiRNAfamilies that are differentially responsive to oxidative stress and discovered 32 new ricemiRNAs. By analyzing 62 small RNA libraries that.