Expression of Arabidopsis polycistronic non-homologous miRNA clusters and selected targets in different organs. (a) Detection by RT-PCR analysis of the expression of Arabidopsis polycistronic non-homologous clusters as single transcriptional units: Ath-MIR859-774, Ath-MIR397b-857, Ath-MIR850-863, and Ath-MIR851-771. Total RNAs from wild-type (Col-0) seedlings were used for DNAse I treatment and cDNA synthesis to perform RT-PCR reactions. A control without reverse transcriptase (-RT) was systematically included to check for the absence of genomic DNA. Specificity of PCR amplicons was verified by sequencing. (b) Expression analysis by RT-PCR of the different Arabidopsis polycistronic non-homologous clusters (Ath-MIR859-774, Ath-MIR397b-857, Ath-MIR850-863, and Ath-MIR851-771) in different organs (R, roots; RL, rosette leaves; S, stems; CL, cauline leaves; F, flowers). (c) Expression analysis by RT-PCR of selected Ath-MIR859-774 targets in the same organs (roots, rosette or cauline leaves, stems, flowers) as in (b). The Arabidopsis Information Resource database entry TAIR:At3g49510 was used as an Ath-miR859 validated target (by 5' RACE (rapid amplification of cDNA ends) PCR) , and TAIR:At3g19890 for Ath-miR774 . At3g18780 encoding an ACTIN isoform was used as RNA loading control.