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l h e tropane alkaloid scopolamine is synthesized in the pericycle of branch roots in certain species of the Solanaceae. l h e enzyme responsible for the synthesis of scopolamine from hyoscyamine is hyoscyamine C&hydroxylase (H6H). The gene for H6H was isolated from Hyoscyamus niger. It has an exon/intron organization very similar to those for ethylene-forming enzymes, suggesting a common evolutionary origin. The 827-bp 5' flanking region of the H6H gene was fused to the j3-glucuronidase (CUS) reporter gene and transferred to three solanaceous species by Agrobacferiummediated transformation systems: H. niger and belladonna (Atropa belladonna), which have high and low levels, respedively, of H6H mRNA in the root, and tobacco (Nicotiana tabacum), which has no endogenous H6H gene. Histochemical analysis showed that CUS expression occurred in the pericycle and at the root meristem of transgenic H. niger hairy roots, but only at the root meristem of hairy roots and plants of transgenic tobacco. In transgenic hairy roots and regenerated plants of belladonna, the root meristem was stained with CUS activity, except for a few transformants in which the vascular cylinder was also stained. lhese studies indicate that the cell-specific expression of the H6H gene is controlled by some genetic regulation specific to scopolamine-producing plants.Secondary metabolites with diverse chemical structures are usually synthesized in some plant tissues at certain developmental stages. The rates of metabolite formation are often greatly infliienced by interna1 hormone balances and extemal stimuli, such as light and pathogen attack. Our knowledge of how the expression of structural genes encoding biosynthetic enzymes involved in secondary metabolism is controlled comes primarily from genetic and molecular studies of the biosynthesis of flavonoids, typically anthocyanin pigments (Dooner et al., 1991). These studies have shown that the distribution of anthocyanins in plant tissues is detennined by the expression pattems of, and the interactions among, specific transcriptional activators.In the absence of similar genetic and molecular studies of other secondary metabolites, it is not certain whether, and, if so, how much, the basic regulatory mechanisms that have been identified in the anthocyanin pathway can be extended to other groups of secondary metabolites in plants. Flavonoids are atypical among secondary products in that a11

A 2275-marker genetic map of rice (Oryza sativa L.) covering 1521.6 cM in the Kosambi function has been constructed using 186 F2 plants from a single cross between the japonica variety Nipponbare and the indica variety Kasalath. The map provides the most detailed and informative genetic map of any plant. Centromere locations on 12 linkage groups were determined by dosage analysis of secondary and telotrisomics using >130 DNA markers located on respective chromosome arms. A limited influence on meiotic recombination inhibition by the centromere in the genetic map was discussed. The main sources of the markers in this map were expressed sequence tag (EST) clones from Nipponbare callus, root, and shoot libraries. We mapped 1455 loci using ESTs; 615 of these loci showed significant similarities to known genes, including single-copy genes, family genes, and isozyme genes. The high-resolution genetic map permitted us to characterize meiotic recombinations in the whole genome. Positive interference of meiotic recombination was detected both by the distribution of recombination number per each chromosome and by the distribution of double crossover interval lengths.

A group of about 300 evenly distributed DNA markers from a high density RFLP linkage map of rice constructed using an F2 population derived from a japonica variety, Nipponbare, and an indica variety, Kasalath, were used to evaluate gene order and genetic distance in four other rice mapping populations. The purpose of this study was to determine the degree to which information gained from the high density linkage map could be applied to other mapping populations, particularly with regard to its utility in bridging quantitative traits and molecular and physical mapping information. The mapping populations consisted of two F2 populations derived from Dao Ren Qiao/Fl-1084 and Kinandangputi/Fl-1007, recombinant inbred lines from Asominori/IR24, and a backcross population from Sasanishiki/Habataki//Sasanishiki. All DNA markers commonly mapped in the four populations showed the same linkage groups as in the Nipponbare/Kasalath linkage map with conserved linkage order. The genetic distance between markers among the different populations did not vary to a significant level in any of the 12 chromosomes. The differences in some markers could be attributed to the size of the population used in the construction of the linkage maps. Furthermore, the conservation of linkage order found in the distal region of chromosomes 11 and 12 was also confirmed in the RFLP maps based on the four populations of rice. These suggest that any major genetic information from the Nipponbare/Kasalath map can be expected to be approximately the same in other crosses or populations. This high density RFLP linkage map, which is being utilized in constructing a physical map of rice, can be very useful in interpreting genome structure with great accuracy in other populations. Key words : linkage map, japonica, indica, gene order, genetic distance.

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