Nucleotide Sequence of an Arabidopsis thaliana Turgor-Responsive cDNA Clone Encoding TMP-A, a Transmembrane Protein Containing the Major Intrinsic Protein Motif

Plants have the capacity of responding to changes in the environment. Water stress is one of the environmental stresses to which a plant might be exposed. Upon exposure to such stress, a plant undergoes a series of physiological and biochemical changes. These changes include the closure of stomata, decrease in photosynthesis, increase in ABA (Zeevart and Creelman, 1988), and alteration in gene expression (Skriver and Mundy, 1990). Here we describe a cDNA clone encoding TMP-A from Arabidopsis thaliana. The protein encoded by it is very homologous to that encoded by the turgorresponsive 7a cDNA cloned from pea (Guerrero et al., 1990). An Arabidopsis cDNA expression library from etiolated seedlings in XZap was screened by DNA hybridization using random-priming-labeled cDNA encoding RNP-T, an RNAbinding protein (Bar-Zvi et al., 1992). Approximately 200 clones were isolated from the screening of 3 X 105 phage. Here we describe one of these clones, termed T8. The DNA insert was subcloned to pBluescript and was subjected to restriction and sequence analysis. Sequence analysis revealed that the 2285-bp T8 clone was composed of a 1105-bp cDNA sequence ligated "head to head" to RNP-T cDNA. This 1105bp cDNA contained an open reading frame of 858 bp encoding for 286 amino acid residues (Table I). A search of the Swiss Protein Data Bank indicated that this gene product, termed TMP-A, showed high homology to the protein encoded by the turgor-responsive 7a cDNA cloned from pea (Guerrero et al., 1990). The TMP-A polypeptide is three amino acid residues smaller than that encoded by 7a. The overall amino acid identity was 84%, whereas similarity was 9 1 %. The nucleotide sequences of the coding regions of these genes showed 74% identity, whereas no significant homology was found in the noncoding sequences. Comparison of the TMP-A and 7a amino acid sequences revealed that there are two insertions in the 7a polypeptide in relation to TMP-A, three amino acids between residues 28 and 29, and one amino acid between residues 158 and 159 of TMP-A. In