ALTERNATIVE SPLICING RESULTS IN 2 DIFFERENT TRANSCRIPTS FOR H-PROTEIN OF THE GLYCINE CLEAVAGE SYSTEM IN THE C-4 SPECIES FLAVERIA-TRINERVIA

Alternative splicing is a well-known post-transcriptional regulatory mechanism in eukaryotic organisms but there are only very few reports on alternative splicing in plants. The analysis of cDNAs encoding H-protein of the glycine decarboxylase multi-enzyme complex from the C-4 species Flaveria trinervia revealed the presence of two transcript populations that differ in the length of their coding regions by six nucleotides. Otherwise, including their 3' nontranslated region, they are identical. From a genomic Southern analysis and from the sequencing of several independent cDNA clones it is evident that both types of transcript are derived from a single-copy gene. This gene, FTgdcsH, has been cloned and sequenced. It comprises four short exons. The two alternative splice sites are located at the end of intron 1. The shorter transcript closely corresponds to published H-protein mRNA sequences from other organisms. The longer transcript encodes two additional alanine residues very close to the N-terminus of the mature H-protein. A quantification of the relative amounts of both transcripts in different organs revealed that, with 80-90% of the total H-protein mRNA, the alternative mRNA dominates in leaves whereas roots contain more of the 'correctly' spliced transcript. It is concluded that, in F. trinervia and with a distinct organ preference, alternative splicing leads to the synthesis of two different H-proteins of the glycine cleavage system.