Genes controlling the regeneration ability of cultured cells have been detected as quantitative trait loci (QTLs). In rice, five QTLs associated with the regeneration ability of seed callus have been detected and tentatively named as follows:qRg1 for chromosome 1, qRg2 for chromosome 2, and qRg4a, qRg4b and qRg4c for chromosome 4 (Taguchi-Shiobara et al. 1997). In barley, a locus on chromosome 2H conferring the regeneration ability of callus derived from immature embryo has been found and named Shd1 (Komatsuda et al. 1995). Using several markers dispersed on the whole barley genome, four QTLs were found and named Qsr1, Qsr2 Qsr3 and Qsr4 (Mano et al. 1996). The correspondence between barley QTL and rice QTL was examined, because these diploid grass species have a simple genome structure without genome duplication.

RFLP markers linked to the five barley QTLs controlling the regeneration ability of cultured cells (Komatsuda et al. 1995, Mano et al. 1996) were located in rice linkage map described by Lin et al. (1998). The rice linkage map was constructed using 98 BC₁F₅ lines derived from two varieties, Nipponbare and Kasalath. To cover the putative region of the barley QTLs, 26 barley markers were selected from Mano et al. (1996). Three markers, including one of the aforementioned 26 markers, were selected from Komatsuda et al. (1995).

Twelve of the 28 probes studied showed polymorphic bands between Nipponbare and Kasalath. These were mapped to 16 locations on the rice linkage map (data not shown). Some of the probes that showed multiple polymorphic bands were located on two or three loci. Two of the 16 barley markers, MWG865 linked to barley Qsr1 and Shd1 on chromosome 2H, and ABC171 linked to Qsr2 on chromosome 3H, were located near rice qRg1 on chromosome 1 (Fig.1). MWG503, CDO588 and ABG014, linked to barley Qsr1 and Shd1, were located near rice qRg4b on chromosome 4. CDO588 was also located near rice qRg2 on chromosome 2. The order of ABG014-CDO588-MWG503 was conserved between barley chromosome 2H and rice chromosome 4. The order of the other markers was not conserved between rice and barley (data not shown).

Our results suggest that barley Qsr1 and Shd1, and rice qRg4b originated from the same chromosomal block of ancestral species of grass. This agrees with earlier findings that the long arm of barley 2H shares a conserved segment with rice chromosome 4 (Van Deynze et al 1995). Further genetic analysis is needed to clarify the precise location and function of each QTL.

Acknowledgment

We thank Drs. A. Kleinhofs, Washington State University, USA., M. Sorrells, Cornell University, USA and A. Graner, Institute for Resistance Genetics, Germany, for providing us the probes. Thanks are also due to Drs. S. Y. Lin, M. Yano and T. Sasaki, Rice Genome Research Program, and Dr. Mano, National Institute of Agrobiological Sciences, for map construction.

References

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Lin, S. Y., T. Sasaki and M. Yano, 1998. Mapping quantitative trait loci controlling seed dormancy and heading date in rice, Oryza sativa L., using backcross inbred lines. Theor. Appl. Genet. 96: 997-1003.

Mano, Y., H. Takahashi, K. Sato and K.Takeda, 1996. Mapping genes for callus growth and shoot regeneration in barley. Breeding Science 46: 137-142.

Taguchi-Shiobara, F., S.Y. Lin, K. Tanno, T. Komatsuda, M. Yano, T. Sasaki and S. Oka, 1997. Mapping quantitative trait loci associated with regeneration ability of seed callus in rice, Oryza sativa L. Theor. Appl. Genet. 95: 828-833.

Van Deynze, A.E., J.C. Nelson, E.S. Yglesias, S.E. Harrington, D.P. Braga, S.R. McCouch, and M.E. Sorrells, 1995. Comparative mapping in grasses. Wheat relationships. Mol. Gen. Genet. 248: 744-754.