The restoration of male fertility in the sorghum IS1112 C (A3) male-sterile cytoplasm is through a two-gene gametophytic system involving complementary action of the restoring alleles Rf3 and Rf4. To develop markers suitable for mapping rf4, AFLP technology was applied to bulks of sterile and fertile individuals from a segregating BC(3)F(1) population. Three AFLP markers linked to rf4were identified and subsequently converted to STS/CAPS markers, two of which are co-dominant. Based on a population of 378 BC(1)F(1) individuals, two STS/CAPS markers, LW7 and LW8, mapped to within 5.31 and 3.18 cM, respectively, of rf4, while an STS marker, LW9, was positioned 0.79 cM on the flanking side of rf4. Markers LW8 and LW9 were used to screen sorghum BAC libraries to identify the genomic region encoding rf4. A series of BAC clones shown to represent a genomic region of linkage group E were identified by the rf4-linked markers. A contig of BAC clones flanking the LW9 marker represent seed clones on linkage group E, from which fine mapping of the rf4 locus and chromosome walking can be initiated.

We propose that the experimentally observed resistivity upturn of cuprates at low temperatures may be explained by properly accounting for the effects of disorder in a strongly correlated metallic host. Within a calculation of the dc conductivity using real-space diagonalization of a Hubbard model treated in an inhomogeneous unrestricted Hartree-Fock approximation, we find that correlations induce magnetic droplets around impurities, and give rise to additional magnetic scattering which causes the resistivity upturn. A pseudogap in the density of states is shown to enhance both the disorder-induced magnetic state and the resistivity upturns.

We consider a defect in a strongly correlated host metal and discuss, within a slave-boson mean field formalism for the t-tЈ-J model, the formation of an induced paramagnetic moment which is extended over nearby sites. We study in particular an impurity in a metallic band, suitable for modeling the optimally doped cuprates, in a regime where the impurity moment is paramagnetic. The form of the local susceptibility as a function of temperature and doping is found to agree well with recent NMR experiments, without including screening processes leading to the Kondo effect.

Nucleolytic processing of transcripts within mitochondrial orf107, associated with male sterility in sorghum, is regulated by the fertility restoration gene Rf3, conferring 75% cleavage of whole-length transcripts. Two transcript editing sites are 81% and 61% edited in rf3rf3 lines, while these sites are 41% and 10% edited in the remaining whole-length transcripts in an Rf3Rf3 line. RNA editing and processing efficiency in F1 progeny were similar to the Rf3Rf3 parent, and analyses of backcross progeny indicated that all rf3rf3 lines were characterized by high editing efficiency. We postulate that highly edited transcripts within the population are quickly processed in lines carrying Rf3, generating a residual population of poorly edited transcripts. Thus, action of Rf3 may have no direct affect on RNA editing, and may be dependent on a substrate of highly edited transcripts. These data indicate a potentially novel role of RNA editing in gene expression through an influence on the efficiency of transcript processing.

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