Mapping of a spontaneous mutation for early flowering time in maize highlights contrasting allelic series at two-linked QTL on chromosome 8

Only a few mutations affecting flowering time have been detected in maize. We analyzed a spontaneous early mutation, vgt-f7p, which appeared during production of the inbred line F7. This mutation shortens the time from planting to flowering by about 100 growing degree days (GDD), and reduces the number of nodes. It therefore seems to affect the timing of meristem differentiation from a vegetative to a reproductive state. It was mapped to a 6 cM confidence interval on chromosome 8, using a QTL mapping approach. QTL analysis of a mapping population generated by crossing the mutant F7 line (F7p) and the Gaspé flint population showed that vgt-f7p is probably allelic to vgt1, a QTL described in previous studies, and affects earliness more strongly than the Gaspé allele at vgt1. Global analysis of the QTL in the region suggested that there may be two consensus QTL, vgt1 and vgt2. These two QTL have contrasting allelic effects: rare alleles conferring extremely early flowering at vgt1 vs. greater diversity and milder effects at locus vgt2. Finally, detailed syntenic analysis showed that the vgt1 region displays a highly conserved duplicated region on chromosome 6, which also plays an important role in maize flowering time variation. The cloning of vgt1 should, therefore, also facilitate the analysis of the molecular basis of variation due to this second region.