Functional characterization of OsmiR396a in rice (Oryza sativa L.)

miR396 is a conservative microRNA family, which has been shown to be important for plant growth and development. To investigate the functions of miR396 in rice (Oryza sativa L.), we carried out a study on OsmiR396a. We found that OsmiR396a was expressed in various tissues with highest transcriptional level in leaves. Bioinformatic prediction suggested that OsmiR396a targets nine Growth Regulating Factor(GRF) genes, of which four (OsGRF1/2/6/8) were significantly down regulated by overexpression of OsmiR396a (aOE). aOE severely suppressed cell proliferation, leading to dwarf plants with smaller leaves. aOE also resulted in abnormal panicles and spikelets, especially a large proportion of rare conjoined-twin florets. Consistent with these defects, some related genes, including H4-2 and OsRAN2 (involved in cell division), FZP and LAX1 (controlling inflorescence architecture) and various floral organ identity genes (involved in floral development), exhibited significantly altered expressional levels in the aOE plants. Our findings further demonstrated the functional conservation of miR396 across dicot and monocot plants and suggested that OsmiR396a functions mainly by targeting OsGRF genes and indirectly regulating many downstream genes in rice.