Sequence and expression analysis of the Arabidopsis IQM family

Four major families have been found so far to possess the calmodulin binding IQ motif/s in plants: the IQD, the myosin, the CAMTA and the CNGC family. We have systematically identified and characterized a novel IQ motif-containing protein family, IQM, in Arabidopsis (Arabidopsis thaliana) using bioinformatics methods. IQM family contains six-member proteins (IQM1-6) which share sequence homology with a pea heavy metal-induced protein 6 and a ribosome-inactivating protein, trichosanthin, as well as IQ motif. IQM family can be divided into two groups, IQM3 and the other member proteins, based on sequence similarity and phylogenetic analysis of sequences. Though almost constitutive expression patterns were found in various plant organs of 6-week-old plants for IQM1 and 2, the other genes exhibited distinct organ-specific expression patterns. Light irradiation and treatment with heavy metals such as CdCl₂ or Pb(NO₃)₂ and high concentrations of mannitol or NaCl also changed expression of each IQM gene in a distinct manner in 7-day-old seedlings. However, treatment with various hormones, such as auxin, abscisic acid, gibberellin, methyl jasmonate and ethylene precursor, did not affect gene expression significantly. These results suggest that each IQM family gene plays a different role in plant development and responses to environmental cues.