Nucleotide Sequence of an Arabidopsis thaliana Turgor-Responsive TMP-B cDNA Clone Encoding Transmembrane Protein with a Major Intrinsic Protein Motif

Water is one of the most important elements in sustaining life. Therefore, shortage of water produces a stress on any living organism. Plants exposed to water stress undergo a series of physiological, biochemical, and molecular changes. The nature of the response varies with the severity and duration of the stress. Some of these responses include closure of stomata, decrease in photosynthesis, increase in ABA leve1 (Zeevart and Creelman, 1988), and alteration in gene expression (Skriver and Mundy, 1990; Bray, 1991). Here we describe a cDNA clone encoding TMP-B from Arabidopsis thaliana. The protein encoded by it is a second member of the gene family of the recently cloned A. thaliana TMP-A and is very homologous to that encoded by the turgor-responsive 7a cDNA cloned from pea (Guerrero et al., 1990). Screening of the cDNA library is described elsewhere (BarZvi et al., 1992; Shagan and Bar-Zvi, 1993). Here we describe one of these clones, t emed T4. The DNA insert was subcloned to pBluescript and was subjected to restriction and sequence analysis. Sequence analysis revealed that the 21 88bp T4 clone is composed of a 1057-bp cDNA sequence ligated “head to head“ to RNP-T cDNA. It is interesting that TMPA was also isolated as a ligate with RNP-T. We cannot explain this coincidence. The 1057-bp cDNA contained an open reading frame of 858 bp encoding 286 amino acid residues (Table I). The TMPB polypeptide, like the TMP-A polypeptide, is shorter by three amino acid residues than that encoded by the turgorresponsive 7a cDNA cloned from pea (Guerrero et al., 1990). The overall amino acid identities of TMP-B with TMP-A and 7a are 93 and 84%, whereas similarities are 96.5 and 91%, respectively. The nucleotide sequence of the coding region of TMP-B showed 82% identity with TMP-A and 74% identity with 7a. Of the 286 codons, 137 were altered between TMPA and TMP-B. Eighty percent of these changes are in the third position of the codon. The nucleotide change in 118 of the altered codons did not result in a change of the amino acid encoded by it; thus, the two polypeptides differ in only