Generation and characterization of a tomato DCL3 silencing mutant

DICER-like 3 (DCL3) is a major player in heterochromatic 24-nucleotide siRNA and long miRNA biogenesis and mutants have been characterized from Arabidopsis and rice. Here, a tomato DCL3 mutant was generated through the use of trans-activated artificial microRNA and characterized. Global tomato DCL3 (SlDCL3) silencing was induced by crossing the generated responder line (OP:amiRDCL3) with constitutive driver line. Constitutive trans-activation knocked down SlDCL3 levels by ~77%, resulting in dramatically decreased 24-nucleotide small RNA levels, but a significant increase in 21- and 22- nucleotide small RNAs, which was correlated with specific upregulation of SlDCL4 and SlDCL2b. Moreover, in the majority of small RNA-generating loci an almost complete overlap between the control and 35S>>amiRSlDCL3 siRNA signatures, was observed, strongly suggesting that the reduction in 24-nucleotide siRNAs was compensated by increased biogenesis of 21-22 nt siRNAs from the same genomic sequences. Collectively, these results suggest the requirement of SlDCL3 for the biogenesis of 23-24 nt sRNAs and its substitution by SlDCL4 and SlDCL2b, which function in the biogenesis of 21- and 22-nt small RNAs. In addition, differential expression between control and SlDCL3-silenced small RNAs indicated a significant reduction in the abundance of 24-nt putative long miRNAs, which was validated by northern blots, implicating SlDCL3 in their biogenesis. Overall design: Examination of small RNA populations in control (35S:LhG4) and SlDCL3 silenced seedlings (35S>>amiRSlDCL3) 2 biological replicates each