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The heterochronic maize mutant Corngrass1 results from overexpression of a tandem microRNA


Retention of juvenile traits in the adult reproductive phase characterizes a process known as neoteny, and speculation exists over whether it has contributed to the evolution of new species. The dominant Corngrass1 (Cg1) mutant of maize is a neotenic mutation that results in phenotypes that may be present in the grass-like ancestors of maize. We cloned Cg1 and found that it encodes two tandem miR156 genes that are overexpressed in the meristem and lateral organs. Furthermore, a target of Cg1 is teosinte glume architecture1 (tga1)1, a gene known to have had a role in the domestication of maize from teosinte. Cg1 mutant plants overexpressing miR156 have lower levels of mir172, a microRNA that targets genes controlling juvenile development2. By altering the relative levels of both microRNAs, it is possible to either prolong or shorten juvenile development in maize, thus providing a mechanism for how species-level heterochronic changes can occur in nature.

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Figure 1: Analysis of the Cg1 phenotype.
Figure 2: Cloning of the Cg1 gene.
Figure 3: Analysis of Cg1 target genes.
Figure 4: Expression of MIR156 and target genes.

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The authors thank B. Li for his assistance with the isolation of the flanking sequences for Cg1-Pio allele, E. Unger for her helpful discussions and C. Lunde and E. Bortiri for reviewing the manuscript. G.C. was supported by US Department of Agriculture National Research Initiative grant 2004-03387. S.H. was supported by the US Department of Agriculture-Agricultural Research Service. K.S. was supported by the University of California Leadership Excellence through Advanced Degrees (LEADS) research program.

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Authors and Affiliations



A.M.C. did the experiments described in Figure 2a,b and Supplementary Figure 1c. K.S. helped with positional cloning of Cg1-ref (Figs. 2c and 3b). G.C. carried out the analysis of Cg1-ref and analyzed the expression patterns of the microRNAs and target genes (Figs. 1, 2c–j, 3 and 4). G.C. wrote the manuscript with help from S.H. and A.M.C.

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Correspondence to George Chuck.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Fig. 1

Corngrass1 epidermal peels and expression in transgenic lines. (PDF 815 kb)

Supplementary Table 1

Primers used in this study. (PDF 52 kb)

Supplementary Note (PDF 157 kb)

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Chuck, G., Cigan, A., Saeteurn, K. et al. The heterochronic maize mutant Corngrass1 results from overexpression of a tandem microRNA. Nat Genet 39, 544–549 (2007).

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