2 CLASSES OF ISOCITRATE LYASE GENES ARE EXPRESSED DURING LATE EMBRYOGENY AND POSTGERMINATION IN BRASSICA-NAPUS L

We have analyzed the structure of genes encoding the glyoxylate cycle enzyme isocitrate lyase from Brassica napus L. and their expression du ring embryogeny and postgermination. Restriction mapping, nucleotide s equence, and DNA gel blot hybridization analyses of cDNA and genomic c lones indicated that there are approximately six isocitrate lyase gene s in the B. napus genome that can be divided into at least two subfami lies based upon their divergence in 5' and 3' untranslated regions. We showed previously that isocitrate lyase mRNA accumulates during late embryogeny and postgermination. Here, we present results which indicat e that several isocitrate lyase genes are expressed at both stages of development. First, gene-specific probes were used to show that mRNAs encoded by representatives of both gene subfamilies accumulated in bot h late maturation stage embryos and in seedlings of B. napus. Second, a single B. napus isocitrate lyase gene, together with 3.5 kb and 1.4 kb of 5' and 3' flanking regions, respectively, was expressed in both embryos and seedlings of transgenic tobacco plants. The results indica ted that accumulation of isocitrate lyase in late embryogeny and postg ermination does not result from the alternate expression of distinct m embers of the gene family.