The yeast Saccharomyces cerevisiae has at least six species of acid and alkaline phosphatases with different cellular localizations, as well as inorganic phosphate (P_i) transporters. Most of the genes encoding these enzymes are coordinately repressed and derepressed depending on the P_i concentration in the growth medium. The P_i signals are conveyed to these genes through a regulatory circuit consisting of a set of positive and negative regulatory proteins. This phosphatase system is interested as one of the best systems for studying gene regulation in S. cerevisiae due to the simplicity of phenotype determination in genetic analysis. With this methodological advantage, considerable amounts of genetic and molecular evidence in phosphatase regulation have been accumulated in the past twenty-five years. This article summarizes the current progress of research into this subject.

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Distribution of wheat retrotransposon families (families 1 to 7) was examined in 11 Gramineae species by the use of representative reverse transcriptase domain clones selected from six of the seven wheat retrotransposon families previously identified as probes. The homologues of families 3, 4, 5, and 7 retrotransposons were detectable only in the Pooideae species, suggesting that the distribution of the retrotransposons related to these families is restricted to the Pooideae subfamily. The representatives of families 1 and 2, distantly related to families 3 to 7, revealed homologues additionally in the species outside the Pooideae subfamily including rice. These results suggest that the retrotransposons related to the former families have wider distribution than those related to families 3, 4, 5, and 7. Analysis of a wheat genomic clone confirmed that the family 1 representative reverse transcriptase domain clone is a Ty1-copia group retrotransposon derivative, which we have named Tar1. On the basis of these results, the origin of wheat retrotransposon families is discussed.

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Restriction fragment length polymorphism (RFLP) in the reverse transcriptase domain of family 1 retrotransposons was investigated in the genera Triticum and Aegilops. On the basis of the TaqI restriction site distribution within or near the reverse transcriptase domain, we defined the four types (I-IV) of the family 1 wheat retrotransposons. The type I elements are assumed to have been present much before the differentiation of the genera because they distribute in rye and barley. On the other hand, the type II-IV elements appeared to have occurred during speciation of Triticum and Aegilops species and were transmitted vertically from species of lower ploidy to those of higher ploidy, because they distribute in most of the polyploid species whereas they are detectable only in six of 15 diploid species. These findings suggest a possibility that the genomes carrying the new family 1 retrotransposons have been preferred in successful establishment of polyploid species.

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Near-isogenic lines of alloplasmic wheat for the Rf3 gene controlling fertility restoration against the cytoplasm of Triticum timopheevi were developed by successive backcrossing of Chinese Spring to the F₁ plants between (timopheevi)-CS (male sterile) and T. spelta (carrying Rf3). The resultant three BC₃F₁ plants were self-pollinated so as to obtain 125 BC₃F₂ progenies. Using this population, we precisely mapped the Rf3 gene on the short arm of wheat chromosome 1B (1BS) of the RFLP linkage map. The Rf3 gene was localized at a position 1.2 cM and 2.6 cM distant from Xcdo388 and Xabc156, respectively. The genetic distances of Rf3 from Nor and Gli-B1 were calculated to be 22.3 cM and 18.6 cM, respectively, supporting previous data. Estimation of the physical distance of the region suggets that the Rf3 gene resides within 500 kbp from the adjacent RFLP markers. The marker order of the genetic map corresponded to that of the cytological map, except for the position of Xbcd98. Comparison between genetic and cytological maps clearly shows that RFLP markers are unevenly distributed throughout the chromosome arm, and recombinations took place unequally in the chromosome arm.

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