Downregulation of miR172 results in compact spikes. (A) The MIM172 vector, showing the miR172 complementary site including the extra bases that preclude cleavage. ZmUbi, maize UBIQUITIN promoter. (B,C) Expression level of mature miR172 (B) and AP2-5 combined homoeologs (C) estimated by qRT-PCR in four independent MIM172 transgenic lines. Expression levels were normalized to the Kronos control (n=4). (D) Primary spike of Kronos and the different MIM172 transgenic plants 3 weeks after heading. Scale bar: 1 cm. (E,F) Spike length (from the base of the first and last spikelets) (E) and spikelets per cm (F) in the primary spike of Kronos and the different transgenic plants 3 weeks after heading (n=10). (G) Threshability (grains threshed in one pass through an electric thresher/total number of grains, n=8). No statistical analysis is presented for the threshability data because values were 100% for all plants in two MIM172 transgenic lines. All bars represent mean±s.e.m. and asterisks indicate a statistically significant difference to the wild-type control (*P<0.05, **P<0.01, ***P<0.001) by Dunnett's test.