Characterization of ES147, a salt stress regulated protein kinase from Lophopyrum elongatum

The ESI47 serine/threonine protein kinase from Lophopyrum elongatum was investigated to elucidate its potential role in salt tolerance and salt stress response. The yeast two-hybrid system was used to screen a cDNA Arabidopsis library and identify proteins that interact with the ESI47 kinase. Six partial DNA sequences encoding a 33 kDa oxygen-evolving enhancer precursor protein (OEE1) from the photosystem II oxygen-evolving complex were identified which showed an interaction with the ESI47 kinase. Sequence analysis showed that the partial length OEE1 clones were missing the first 81 or 82 amino acids at the amino-terminus of the protein. This region serves as a transit peptide that is required for import of precursor proteins into the chloroplast and is later cleaved. The full length OEE1 clones from Triticum aestivum and Arabidopsis were subcloned into the yeast two-hybrid library vector to determine whether the ESI47 kinase could interact with the OEE1 from either of these species. An interaction between the ESI47 kinase and the full length OEE1 precursor was not observed, which suggests that the kinase interacts with the mature OEE1 protein in the chloroplast. Northern analysis was used to compare the expression of ESI47 homologues, in different species of wheat grasses, which have differing degrees of salt tolerance. ESI47 expression was not observed with northerns prepared with total RNA nor with poly-(A)+ RNA samples, and a correlation between the ESI47 expression and salt tolerance was therefore not established in this work.