Molecular cloning, characterization, and expression of wheat cystatins.

We cloned four kinds of cDNAs of wheat cystatins (WCs), WC1, WC2, WC3, and WC4, from the seed. They had 47-68% amino acid sequence similarities to other plant cystatins. WC1, WC2, and WC4 had 63-67% similalities to one another while 93% of amino acids were identical between WC1 and WC3. This suggested that WCI, WC2, and WC4 should be regarded as the isoforms of wheat cystatins. The mRNAs for WC1, WC2, and WC4 were all expressed in seed at an early stage of maturation and, after that, their quantities decreased gradually. However, each of the mRNAs was again expressed one day after the start of germination and the expression continued for the following five days. WC1 seemed to be expressed at a higher level than WC2 and WC4. Immunostaining for looking at site-specific expression of each WC demonstrated that both WC1 and WC4 existed in the aleuron layer and embryo, but in the endosperm the only existing species was WC1. Differences in mRNA level and tissue localization found for the WCs may suggest their differential physiological roles.