Isolation and characterization of full-length cDNA clones of the giant taro (Alocasia macrorrhiza) trypsin/chymotrypsin inhibitor.

A full-length cDNA encoding the 206 amino acid open reading frame of a trypsin/chymotrypsin inhibitor abundant in the corms of giant taro (Alocasia macrorrhiza) was isolated. An internal fragment was cloned using degenerate primers corresponding to a region of the mature protein sequence and the 'rapid amplification of cDNA ends' (RACE) method used to generate a composite cDNA sequence. The length of the cDNA was close to the predicted size of the corresponding transcript deduced from northern blot analysis of corm mRNA. The inhibitor was expressed strongly in the mature corm, at low levels in leaf blades and petioles but not in roots. Southern blot analysis of the giant taro DNA indicated that this inhibitor is encoded by a small multigene family and this was further supported by the isolation of two different sequence classes from corm cDNA using primers to the ends of the composite sequence.