2 CLOSELY-RELATED CDNAS ENCODING STARCH BRANCHING ENZYME FROM ARABIDOPSIS-THALIANA

Two starch branching enzyme (SEE) cDNAs were identified in an Arabidop sis seedling hypocotyl library using maize Sbe1 and Sbe2 cDNAs as prob es. The two cDNAs have diverged 5' and 3' ends, but encode proteins wh ich share 90% identity over an extensive region with 70% identity to m aize SEE IIb [12]. Genomic Southern blots suggest that the two cDNAs a re the products of single, independent genes, and that additional, mor e distantly related SEE genes may exist in the Arabidopsis genome. The two cDNAs hybridize to transcripts which show similar expression patt erns in Arabidopsis vegetative and reproductive tissues, including see dlings, inflorescence rachis, mature leaves, and flowers. This is the first report of the identification of cDNAs encoding two closely relat ed starch branching enzymes from the same species.