A root-specific O-methyltransferase gene expressed in salt-tolerant barley.

A cDNA encoding an O-methyltransferase (OMT) was isolated from salt-tolerant barley roots by subtraction hybridization with cDNAs of salt-tolerant barley roots as a tester cDNA and cDNAs of the salt-sensitive barley roots as a driver cDNA. The deduced amino acid sequence showed significant identity with plant caffeic acid/5-hydroxyferulic acid OMTs. Southern blot analysis showed that the OMT gene was a single copy in both salt-tolerant and -sensitive barley. The cloned gene was expressed in a wheat germ cell-free system to produce the OMT, which had methylating activity for caffeic acid. Northern blot analysis showed that the OMT gene was expressed constitutively in the salt-tolerant barley roots and the expression level was increased 1.5 times by salt stress, but the salt-sensitive barley showed no expression of the gene in roots and leaves.