Molecular mapping of genes for opposite leafing in maize using simple-sequence repeat markers

Maize with opposite phyllotaxy (OP) and also initiating ears in opposite pairs is an aberrant mutant and also precious material for maize breeding and plant evolution studies. Mapping and identifying the markers closely linked to genes for the OP trait are essential for cloning the gene and marker-assisted selection in breeding. We established H14D, a near-isogenic line of the OP trait with H53 genetic background. We found that the OP trait is regulated by two independent dominant genes with mutually complementary relations, named Opp-1 and Opp-2. Screening of seven simple-sequence repeat (SSR) markers among the 105 pairs of SSR primers showed polymorphism between the inbred lines H14D and H53. The polymorphic SSR markers were then used to determine linkage with the trait in an F(2) population with 441 progeny, suggesting that SSR marker umc2094 in the Bin2.01 region is linked with Opp-1 at 6.7 cM, and bnlg1831 in Bin2.06 is linked with Opp-2 at 6.1 cM. Further investigation showed that bnlg1092 and umc1028 are linked to Opp-1 and Opp-2 genes, with genetic distances of 12.2 and 1.9 cM. It was also found that the four SSR markers flank the two OP genes, respectively. These results will be useful for marker-assisted selection breeding of OP maize and will also strengthen the basis for cloning of the opposite leafing gene.