Toshiyuki Komori

Current Status of Binary Vectors and Superbinary Vectors

A binary vector was invented soon after it had been elucidated that crown gall tumorigenesis was caused by genetic transformation of plant cells with a piece of DNA, T-DNA for transferred DNA, from a Ti plasmid (tumor-inducing plasmid) harbored by the soil bacterium Agrobacterium tumefaciens ([

Differential expression of plastidic aldolase genes in Nicotiana plants under salt stress

Two homologous genes of plastidic fructose-1,6-bisphosphate aldolase (AldP) isozymes were isolated from green leaves of a salt stress-tolerant Nicotiana species, Nicotiana paniculata, by differential screening. The products of the corresponding genes, NpAldP1 and NpAldP2, were 91% identical to each other and 70-85% identical to the other known plant plastidic aldolases. Although these two genes showed similar organ-specific expression and daily cycles, their responses to salt stress differed: mRNA accumulation of NpAldP2 increased, but that of NpAldP1 slightly decreased. The mRNA accumulations of their counterparts of two other Nicotiana species, NeAldP1 and NeAldP2 (Nicotiana excelsior), and NaAldP1 and NaAldP2 (Nicotiana arentsii) were studied under the same stress condition. N. arentsii conserved accumulation profiles similar to N. paniculata, but N. excelsior did not. In N. excelsior, accumulation of NeAldP1 decreased to 50% of the control after stress and gradually recovered thereafter, whereas accumulation of NeAldP2 temporarily decreased and reached 250% of the control by the third day of stress. Southern blot analysis indicated that NpAldP1, NpAldP2, NaAldP1, and NaAldP2 include one or two closely related genes and NeAldP1 and NeAldP2 several.

Fine genetic mapping of the nuclear gene, Rf-1, that restores the BT-type cytoplasmic male sterility in rice (Oryza sativa L.) by PCR-based markers

The Rf-1 gene restores the pollenfertility disturbed by the BT-type malesterile cytoplasm. Nine restrictionfragment length polymorphism (RFLP) markerson chromosome 10, where the Rf-1 geneis located, were converted to PCR-basedmarkers. Genetic analysis was conductedusing the nine markers and a segregatingpopulation consisting of 1042 plants. As aresult, the Rf-1 gene was mappedbetween S12564 Tsp509I and C1361 MwoI. The genetic distance of the twomarker loci was estimated as 0.3 cM. Basedon the map information of the Rf-1gene, it will be possible to introduce alimited chromosomal segment of the Rf-1 region derived from a donor intojaponica rice varieties efficiently andeffectively by marker-assisted selection(MAS). Also, examination of seed purity ofhybrid rice varieties and their parentallines will be facilitated. Furthermore,judging from the genetic distance from theRf-1 locus to S12564 Tsp509Iand C1361 MwoI loci, it seems thatthe Rf-1 gene could be isolated bychromosomal walking from either or both ofthe two marker loci.

Comparative study of the Nicotiana species with respect to water deficit tolerance during early growth

Sixty Nicotiana species were examined for tolerance against various osmotica for seed germination and seedling growth in vitro. The species showed a wide variety of tolerance, and based on the results of the in vitro tests, 31 species were selected and further evaluated for salt and drought tolerance in a glasshouse. The degrees of tolerance of germination among the 57 species toward NaCl were approximately related to those toward mannitol, indicating that the osmolarity plays a majorrole in seed germination. However, the responses during the seedling growth differed in NaCl and mannitol or drought, and there was no correlation between salt and drought tolerance. Based on the responses in vitro and in the glasshouse, N. paniculata and N. excelsior were selected as the salt tolerant species, and N. arentsii as the salt sensitive species. The degrees of accumulation of dry matter and of Na+ in the leaves were different in the two tolerant species; during NaCl treatment, N. paniculata and N. arentsii accumulated less dry matter relative to the control plants than N. excelsior, and N. paniculata accumulated more Na+ in its leaves than N. excelsior and N. arentsii. It is assumed that the two salt tolerant species have different mechanisms for tolerance to the salt.