CHARACTERIZATION OF A CDNA CLONE FROM SALT-TOLERANT ALFALFA CELLS THAT IDENTIFIES SALT-INDUCIBLE ROOT-SPECIFIC TRANSCRIPTS

A novel cDNA clone has been isolated by differential screening of a cDNA library from salt-tolerant alfalfa (Medicago sativa) cells using cDNA probes derived from poly-A(+) RNAs from salt-sensitive and salt-tolerant callus. This clone, which is designated pA9, contains a 600 bp insert that hybridizes to a 1.6 kb RNA transcript. The concentration of this transcript increases in salt-tolerant callus cells in response to either NaCl or abscisic acid (ABA). By contrast, the concentration of transcripts hydridizing to pA9 decreases in salt-sensitive callus cells in response to salt or ABA. In whole plants, the transcripts detected by clone pA9 occur specifically in roots and cannot be found in leaves. The concentration of these transcripts increases in both salt-sensitive and salt-tolerant plant roots in response to NaCl. There are only a small number of copies of the gene corresponding to pA9 in the alfalfa genome. The sequence of the pA9 insert suggests that it represents a gene encoding a protein related to proline-rich cell wall proteins previously found in tomato, maize, and carrot. Clone pA9 thus identifies a potentially important gene that is regulated in a tissue-specific manner by NaCl.