Developing a transposon tagging system to isolate rust-resistance genes from flax

Summary A line of flax, homozygous for four genes controlling resistance to flax rust, was transformed with T-DNA vectors carrying the maize transposable elements Ac and Ds to assess whether transposition frequency would be high enough to allow transposon tagging of the resistance genes. Transposition was much less frequent in flax than in Solanaceous hosts such as tobacco, tomato and potato. Transposition frequency in callus tissue, but not in plants, was increased by modifications to the transposase gene of Ac. Transactivation of the excision of a Ds element was achieved by expressing a cDNA copy of the Ac transposase gene from the Agrobacterium T-DNA 2 promoter. Progeny of three plants transformed with Ac and 15 plants transformed with Ds and the transposase gene, were examined for transposition occurring in the absence of selection. Transposition was observed in the descendants of only one plant which contained at least nine copies of Ac. Newly transposed Ac elements were observed in 25–30% of the progeny of some members of this family and one active Ac element was located 28.8 (SE=6.3) map units from the L ⁶ rust-resistance gene. This family will be potentially useful in our resistance gene tagging program.     

Nucleotide sequence and phylogenetic implication of the ATPase subunits β and ε encoded in the chloroplast genome of the brown alga Dictyota dichotoma

We have cloned and sequenced the genes atpB and atpE, coding for CF₁ subunits and , respectively, of the chloroplast genome of the brown alga Dictyota dichotoma. Although the coding site of atpE cannot be demonstrated by heterologous Southern hybridizations, a 417 bp reading frame 3 to atpB was identified as the gene atpE by sequence similarities with atpE genes from other sources. A maximum sequence identity of 30% is found between the predicted amino acid sequence of the Dictyota subunit and the corresponding cyanobacterial subunits. Including conserved amino acid replacements, the Dictyota subunit exhibits about 70% sequence similarity with the cyanobacterial and land plant subunits. As in cyanobacteria, the atpE gene does not overlap the preceding gene atpB. The deduced amino acid sequence of atpB is 74–79% identical to the corresponding cyanobacterial and chloroplast subunits. Entirely conserved are regions referred to as the catalytic and/or regulatory sites of ATP formation, including interacting regions between subunits and . A phylogram predicted from F₁/CF₁- subunits of eleven different organisms suggests a common evolutionary origin of plastids from chlorophytes and brown algae.