MiRNAs are important regulators playing important roles in plant development and plant responses to biotic and abiotic stresses as well as in regulating miRNAs themselves and other small RNAs (Bartel 2009; Chen 2009; Chuck et al. 2009; Poethig 2009; Voinnet 2009; Zhu et al. 2009). Many miRNA families have multiple members with different temporal and spatial expression patterns (Palatnik et al. 2007; Nag et al. 2009; Voinnet

2009) . Mature miRNAs usually have multiple targets, which constitute a complicated regulatory network impacting different aspects of plant life (Axtell and Bowman 2008; Bartel 2009; Rubio-Somoza and Weigel 2011).