2 MAIZE GENES ENCODING OMEGA-3-FATTY-ACID DESATURASE AND THEIR DIFFERENTIAL EXPRESSION TO TEMPERATURE

We have isolated two maize cDNAs and the corresponding genes encoding fatty acid desaturase with Arabidopsis thaliana FAD7 gene as a probe. They shared almost 90% identity at DNA sequence level. Northern analys is revealed that both genes are expressed in leaves, but not in roots at normal temperature-and low temperature-growth condition. The overal l level of these transcripts are elevated upon exposure to low tempera ture. The tissue-specific expression and DNA sequence data indicate th at both genes encode plastidic omega-3 fatty acid desaturases. One of them is expressed exclusively at normal temperature but not at 5 OC, w hereas the other is expressed inversely. We, therefore, termed them Zm FAD7 and ZmFAD8, respectively. Among other stresses, high-salt treatme nt induced the accumulation of the ZmFAD7 and ZmFAD8 transcripts in ro ots but drought had no effect on their expression. Cycloheximide induc ed the accumulation of the ZmFAD7 transcript in roots. The genomic clo nes of ZmFAD7 and ZmFAD8 consist of 8 exons and 7 introns as same as i n the cases of A. thaliana FAD7 and FAD8 genes and the sizes of the 6 internal exons were identical among them. A phylogenetic analysis of Z mFAD7, ZmFAD8 amino acid sequences and those originated from other pla nt species is also presented.