The Affymetrix-based monitoring also showed an up-regulation, although modest, of members of the MIR390, MIR397, and MIR408 families(Fig. 3B). Expression data of miRNA primary transcripts is thus in line with the 454 sequencing results and further suggests that miR167, miR171c, miR172,miR390, miR397, and miR408 could potentially undergo nodule-specific transcriptional up-regulation as opposed to being translocated from cell to cell from other parts of roots, as has been reported for some miRNAs (Lin et al., 2008; Pant et al., 2008; Carlsbecker et al., 2010). For further validation, we performed northern hybridization from root and nodule tissue extracts.While miR408 could not be detected under our experimental conditions, we confirmed a higher accumulation of miR167, miR171c, and miR172 in nodules as compared with roots and a modest induction of miR390 and miR397 (Fig. 3C).