Mapping Flowering Time Gene Homologs in Soybean and Their Association with Maturity (E) Loci
- I. M. Tasmaa and
- R. C. Shoemaker *b
Time of flowering is a quantitatively inherited character of agronomic importance in soybean [Glycine max (L.) Merr.]. The genetics of flowering time has been extensively studied in the model plant Arabidopsis thaliana (L.) Heynh. The first objective of this study was to map onto the soybean genetic map orthologous genes known to be involved in photoperiod recognition and time of flowering in A. thaliana and compare their location with previously mapped flowering time quantitative trait loci (QTL). The second objective was to associate the mapped homologs with maturity (E) loci by means of near isogenic lines (NILs). Three single-cross soybean populations, consisting of two recombinant inbred line (RIL) populations and one F2 population, were used in the mapping study. One RIL population, IX132, was developed by crossing PI 317.336 and ‘Corsoy’; the second, IX136, by crossing PI 317.334B and Corsoy. Both plant introductions have been reported to be photoperiod-insensitive while the Corsoy parent has been reported to be photoperiod-sensitive. The RIL populations were previously used to map QTL for flowering time, maturity, and photoperiod-insensitivity in soybean. The F2 population was developed from an interspecific cross between G max (breeding line A81-356022) and G. soja (PI 468.916). Eighteen soybean cDNA clones, identified by BLAST to have high similarities with 18 previously cloned A thaliana flowering time genes, were used as probes in this study. Ten of the 18 cDNA clones were mapped. The cDNAs were mapped onto linkage groups (LGs) A2 (CRY2), B1 and H (COL1), A1 and B2 (PHYA), C1 (DET1 and LD), D2 (AP2), E and K (PHYB), F (COL2), L (FCA), and Q (CCA1). None of the cDNAs were directly associated with previously mapped QTL for flowering time. Forty-one NILs and two recurrent parents (RPs) were used in the association study. Analyses of these candidate genes using contrasting NILs showed that the FCA homolog was associated with maturity locus E3 That FCA is a strong gene candidate for maturity locus E3 is further supported by map position and phenotypic data. Analyses of NILs suggest that the soybean homolog PHYB may be associated with maturity locus E1 However, current data show they mapped in different LGs.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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