Proceedings of the XLV Italian Society of Agricultural Genetics - SIGA Annual Congress
Salsomaggiore Terme, Italy - 26/29 September, 2001
CONSTRUCTION OF A BAC CONTIG SPANNING VGT1, A MAJOR QTL FOR FLOWERING TIME IN MAIZE
SALVI S.*, O’SULLIVAN D.**, SERRANI B.*, EDWARDS K.**, PHILLIPS R.***, TUBEROSA R.*
* Dipartimento di Scienze e Tecnologie Agroambientali, Università di Bologna, Italy
** IARC-Long Ashton Research Station, Bristol, UK.
*** Department of Agronomy and Plant Genetics, University of Minnesota, USA.
BAC, chromosome walking, flowering, maize, positional cloning
Vgt1 (Vegetative to generative transition 1) is a major QTL controlling flowering time in maize. The QTL acts on flowering time mainly by influencing the number of nodes (and therefore leaves) developed by the apical meristem, before entering the reproductive phase. Early works mapped Vgt1 to chr.8L, bin 8.05, in a nearly-isogenic background of the late inbred line N28. Notably, QTLs for flowering time and related traits have been mapped to this chromosomal region in ca. 15 different maize genetic backgrounds. By producing a new large mapping population from the cross N28 x C22-4 (an N28 nearly-isogenic line), and by means of bulk segregant analysis based on AFLP, we narrowed the map position of Vgt1 to a genetic interval of 1.3 cM. The high heritability value of flowering time allowed us to score Vgt1 as a Mendelian gene. Both classical and QTL-interval mapping positioned Vgt1 at 0.3 cM from one AFLP marker. Based on this mapping information a chromosome walking procedure was started. DNA amplicons corresponding to the closest AFLP markers have been cloned and sequenced, and specific PCR assays were produced and used to screen a maize BAC library. A number of BAC clones have been found and ordered. In some cases BAC clones were used as source of new genetic markers. Preliminary data indicates a genetic/physical ratio of <500 kb/cM. A BAC clone likely containing Vgt1 has been isolated and is being molecularly characterized.