Effect of epibrassinolide on tyrosine phosphorylation of the calvin cycle enzymes

Abstract

Two-dimensional electrophoresis was used to separate proteins from crude extracts of pea (Pisum sativum L.) leaves, and thus isolated proteins were subjected to Western blot analysis with monoclonal antibodies against PY20 phosphotyrosine polypeptides. This analysis revealed 44 polypeptides phosphorylated on tyrosine residues. Phosphorylation of some of these proteins was changed under the action of epibrassinolide. Some of these polypeptides were identified by means of MALDI-TOF MS analysis. The results indicate that eight of these proteins belong to the Calvin cycle enzymes, namely, the isoforms of Rubisco large and small subunits, fructose-1,6-phosphate aldolases 1 and 2, and the precursor of α-subunit of Rubisco-binding protein. The observed changes in phosphorylation of these proteins may partly explain the effects of brassinosteroids on photosynthesis. The tyrosine phosphorylation sites were identified in silico for the fragments of polypeptides examined.