Gap junction protein homologue from Arabidopsis thaliana: evidence for connexins in plants

An Arabidopsis thaliana library constructed in the pBluescript expression vector lambda ZAP II (Stratagene) was screened with three affinity-purified antibodies raised against (i) rat liver connexin 32, (ii) a polypeptide from soybean root cells that migrates with a molecular mass of 29 kDa in SDS/polyacrylamide gels and is immunologically related to rat liver connexin, and (iii) a synthetic peptide corresponding to a sequence in rat liver connexin 32. A single clone was obtained whose gene product demonstrated immunological crossreactivity with all three reagents. The cDNA from this clone contained 1171 base pairs and coded for a protein of 280 amino acids with a calculated molecular mass of 32,339 Da (migrates as a 29-kDa polypeptide in SDS/polyacrylamide gels). The sequence homology observed between the 32-kDa polypeptide of Arabidopsis and connexin 32 from rat liver, in conjunction with observed similarities in predicted number and distribution of hydrophobic domains, sites for posttranslational modification, and basic pI, provides strong evidence that the biological range for connexin-type proteins may now be considered to include the plant kingdom.