Over-expression of sly-miR156a in tomato results in multiple vegetative and reproductive trait alterations and partial phenocopy of the sft mutant

Plant microRNAs (miRNAs) are vital components of the translation control system that regulates plant development and reproduction. The biological function of sly-miR156 was investigated by over-expression in tomato plants. Transgenic tomato plants exhibited a drastically altered phenotype, with reduced height, smaller but more numerous leaves, and smaller fruit. The inflorescence structure of sly-miR156 over-expressing plants phenocopied the sft mutant. The putative targets of sly-miR156 were identified by data base search and included six SQUAMOSA PROMOTER BINDING PROTEIN (SBP)-box transcription factor genes. Their expression patterns were then determined in 35S-miR156a and wild type tomato plants. These target genes, as well as the tomato FLOWERING LOCUS T (FT) ortholog SFT, were significantly down-regulated in sly-miR156 over-expressing plants. These studies reveal novel phenotypes regulated by miR156.