24-epibrassinolide-induced growth promotion of wheat seedlings is associated with changes in the proteome and tyrosine phosphoproteome.

Brassinosteroids (BRs) represent a unique class of steroidal plant hormones that display pronounced growth-promoting activity at very low concentrations. Although many efforts have been made to characterize the molecular basis of BR action, little is known about the mechanisms behind the growth-promoting effect of BRs at protein level. Proteomic analysis of response to the steroid plant hormone 24-epibrassinolide (EBR) in wheat seedling shoots (Triticum aestivum L.) was performed using two-dimensional electrophoresis (2-DE) and immunoblotting with highly specific antibodies (PY20) to phosphotyrosine. EBR-modulated proteins and phosphotyrosine polypeptides were identified using MALDI-TOF mass spectrometry. The study revealed that EBR-stimulated growth of wheat seedlings was accompanied by changes in the content of multiple proteins as well as in tyrosine phosphorylation of numerous polypeptides. Among them, 22 differentially accumulated proteins and 13 phosphotyrosine proteins were identified. Based on their performed functions, the identified proteins are involved in physiological processes (photosynthesis, growth, energy and amino acid metabolism) closely associated with intensification of plant metabolism. The EBR-induced changes in protein abundance and tyrosine phosphorylation profile may contribute to growth stimulation of wheat seedlings under the action of EBR. The obtained data suggest an important role for EBR in the activation of protein metabolism underlying fundamental physiological processes, including growth promotion.