No abstract

Transformants of maize inbred A188 were efficiently produced from immature embryos cocultivated with Agrobacterium tumefaciens that carried "super-binary" vectors. Frequencies of transformation (independent transgenic plants/embryos) were between 5% and 30%. Almost all transformants were normal in morphology, and more than 70% were fertile. Stable integration, expression, and inheritance of the transgenes were confirmed by molecular and genetic analysis. Between one and three copies of the transgenes were integrated with little rearrangement, and the boundaries of T-DNA were similar to those in transgenic dicotyledons and rice. F1 hybrids between A188 and five other inbreds were transformed at low frequencies.

SummaryA rice nuclear gene, Rf-1, restores the pollen fertility disturbed by the BT-type male sterile cytoplasm, and is widely used for commercial seed production of japonica hybrid varieties. Genomic fragments carrying Rf-1 were identi®ed by conducting chromosome walking and a series of complementation tests. Isolation and analysis of cDNA clones corresponding to the fragments demonstrated that Rf-1 encodes a mitochondrially targeted protein containing 16 repeats of the 35-aa pentatricopeptide repeat (PPR) motif. Sequence analysis revealed that the recessive allele, rf-1, lacks one nucleotide in the putative coding region, presumably resulting in encoding a truncated protein because of a frame shift. Rice Rf-1 is the ®rst restorer gene isolated from cereal crops that has the property of reducing the expression of the cytoplasmic male sterility (CMS)-associated mitochondrial gene like many other restorer genes. The present ®ndings may facilitate not only elucidating the mechanisms of male sterility by the BT cytoplasm and its restoration by Rf-1 but also isolating other restorer genes from cereal crops, especially rice.

The first intron of castor bean catalase gene, cat-1 was placed in the N-terminal region of the coding sequence of the beta-glucuronidase gene (gusA) and the intron-containing gusA was used with the cauliflower mosaic virus (CaMV) 35S promoter. Using this plasmid, pIG221, the effect of the intron on expression of beta-glucuronidase (GUS) activity was examined in transgenic rice calli and plants (a monocotyledon), and transgenic tobacco plants (a dicotyledon). The intron-containing plasmid increased the level of GUS enzyme activity 10 to 40-fold and 80 to 90-fold compared with the intronless plasmid, pBI221, in transgenic rice protoplasts and transgenic rice tissues, respectively. In contrast, the presence of the intron hardly influenced the expression of the GUS activity in transgenic tobacco plants. Northern blot analysis showed that the catalase intron was efficiently spliced in rice cells while transgenic tobacco plants contained both spliced and unspliced gusA transcripts in equal amounts. Furthermore, the level of the mature gusA transcript in transformed rice calli was greatly increased in the presence of the intron. The catalase intron was removed at the same splice junctions in transgenic rice and tobacco plants. These findings indicate that the stimulating effect of the intron on GUS expression is correlated with an efficient splicing of pre-mRNA and an increased level of mature mRNA.