The Hordeum vulgare signalling protein MAP kinase 4 is a regulator of biotic and abiotic stress responses.

Mitogen activated protein kinase (MAP kinase) signal transduction pathways are important eukaryotic mechanisms for regulating cellular responses to stress. The objective of this work was to investigate the role of the barley MAP kinase HvMPK4 (a homologue of the Arabidopsis MAP kinase AtMPK1) in the plant response to biotic and abiotic stress. Transgenic barley plants bearing antisense or overexpression constructs for HvMPK4 were produced, and RNA blot analysis showed that HvMPK4 gene expression was much reduced in the antisense lines and approximately double in the overexpression lines. Three independent lines of each construct were tested for their response to a fungal pathogen and to salt treatment. The antisense lines were more resistant to the hemibiotrophic fungal pathogen Magnaporthe grisea, and showed enhanced levels of salicylic acid (SA) and of hydrogen peroxide following infection; HvMPK4 is thus a negative regulator of SA production post infection. The overexpression lines had constitutively higher levels of jasmonic acid and enhanced levels of ethylene following infection but were not more resistant to the pathogen. However the overexpression lines showed greater tolerance to abiotic stress, as following 2 weeks of salt treatment these lines showed less reduction in fresh and dry weight, accumulated less salt in the leaves and contained enhanced levels of the osmoprotectant amino acid, proline.