The rice mutants gps1-gps12 (gametophytic pollen sterlity) induced by gamma-irradiation were identified for understanding the pollen development (Yamagata et al., 2007). These mutants cause selective abortion of pollen grains carrying mutant alleles. Heterozygotes for gps4, gps5, gps6 and gps12 showed 54.1%, 48.8%, 50.1% and 51.6% of pollen fertility, respectively, and normal spikelet fertility (Fig. 1 and Yamagata et al., 2007). Here we report linkage mapping of these four genes.
Because homozygotes of gps4, gps5, gps6 and gps12 were not obtained, the heterozygotes were used as seed parents for crossing with a Japonica cultivar Hinohikari to obtain the F2 mapping populations. Evaluation of pollen fertility and linkage mapping followed Yamagata et al. (2007).
In the F2 population of gps4, normal and semi-sterile plants segregated in a 1:1 ratio (normal: semi-sterile = 46:34, χ2 for 1:1 = 1.80, 0.50<P<0.75). This segregation indicated that the semi-sterility observed in this F2 population was controlled by the single male gametophytic gene, gps4. Linkage analysis showed that gps4 was located between the SSR markers, RM5271 and RM5689, on chromosome 10(Fig. 2A). Similarly, gps5, gps6 and gps12 were mapped on chromosomes 2, 7 and 8, respectively (Fig. 2B, C and D). In the genomic region near gps4, gps5, gps6 and gps12, any previously reported gene or ortholog gametophytically acting in pollen formation in rice or Arabidopsis were not found. Gene cloning and detailed characterization of these mutants will provide novel understanding on male gametogenesis in rice.
We sincerely thank Associate Professor Tomio Okai, Institute for Irradiation and Analysis of Quantum Radiation, Kyushu University for the gamma-ray irradiation. This work was supported in part by grants from the Ministry of Agriculture, Forestry and Fisheries of Japan (Integrated research project for plant, insect and animal using genome technology GD2003) and the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant-in-Aid for Scientific Research on Priority Areas 19043013).
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