ACTIVE GRANT:

Positional cloning of earliness per se gene Eps-A1 from Triticum monococcum

USDA-NRI September 2003 - August 2006.

PI: Jorge Dubcovsky

PROJECT ABSTRACT

Flowering time is important for the adaptability of wheat varieties to different environments. We have recently identified a gene in diploid Triticum monococcum that is responsible for large differences in heading date independently of vernalization and photoperiod. This earliness per se gene was designated Eps-A^m1. In a segregating population, plants homozygous for the Eps-A^m1 allele from cultivated accession DV92 flowered an average of 50 to 80 days later than those carrying the allele from wild accession G3116. No overlap in heading date was observed between plants from the two allelic classes, and therefore the Eps-A^m1 gene was mapped as a simple Mendelian gene 0.7 cM distal to RFLP marker Xwg241 on the long arm of chromosome 1A^m. In this project we propose to clone the Eps-A^m1gene using a map based approach. We will construct a high-density map using 3,000 F₂ plants and will use PCR markers flanking the Eps-A^m1 gene to find recombination events in this region. We will determine the Eps-A^m1 genotype of the recombinant F₂ plants by progeny tests of 25 F₃ plants that will be individually genotyped with linked marker WG241. Markers will be generated from mapped wheat ESTs and from the colinear rice genome sequence. Markers flanking the Eps-A^m1 gene at less than 0.05 cM will be used to construct a physical contig using the T. monococcum BAC library. BACs from the physical contig will be sequenced and genes will be identified using a combination of computational and experimental methods. Candidate genes for Eps-A^m1 will be identified by comparison with known function genes from other species, expression profiling, and transgenic approaches

PUBLICATIONS

Bullrich L., M.L. Appendino, G. Tranquilli, S. Lewis, and J. Dubcovsky. 2002. Mapping of a thermo-sensitive earliness per se gene on Triticum monococcum chromosome 1A^m. Theor. Appl. Genet. 105: 585-593.

Abstract: An earliness per se gene, designated Eps-A^m1, was mapped in diploid wheat in F₂ and single seed descent mapping populations from the cross between cultivated (DV92) and wild (G3116) Triticum monococcum accessions. A QTL with a peak on RFLP loci Xcdo393 and Xwg241, the most distal markers of the long arm of chromosome 1A^m, explained 47% of the variation in heading date (LOD score 8.3). Progeny tests for the two F_2:3 families with critical recombination events between Xcdo393 and Xwg241 showed that the gene was distal to Xcdo393 and linked to Xwg241. Progeny tests and replicated experiments with line#3 suggested that the Eps-A^m1 was distal to Xwg241. This gene showed a large effect on heading date in the controlled environment experiments, and a smaller, but significant effect under natural conditions. Eps-A^m1 showed significant epistatic interactions with photoperiod and vernalization treatments, suggesting that the different classes of genes affecting heading date interact as part of a complex network that control the timing of flowering induction. Besides its interactions with other genes affecting heading date, Eps-A^m1 showed a significant interaction with temperature. The effect of temperature was larger in plants carrying the DV92 allele for late flowering than in those carrying the G3116 allele for early flowering. Average differences in heading date between the experiments performed at 16°C and 23°C were approximately 11 days (P<0.001) for the lines carrying the Eps-A^m1 allele for early flowering but approximately 50 days (P<0.0001) for the lines carrying the allele for late flowering. The large differences in heading time (average 80 days) observed between plants carrying the G3116 and DV92 alleles when grown at 16°C, suggest that it would be possible to produce very detailed maps for this gene to facilitate its future positional cloning.