A wheat COP9 subunit 5-like gene is negatively involved in host response to leaf rust

The COP9 (constitutive photomorphogenesis 9) signalosome (CSN) is a protein complex involved in the ubiquitin proteasome system and a common host target of diverse pathogens in Arabidopsis. The known derubylation function of the COP9 complex is carried out by subunit 5 encoded by AtCSN5A or AtCSN5B in Arabidopsis. A single CSN5-like gene (designated as TaCSN5) with three homeologues was identified on the long arms of wheat (Triticum aestivum L.) group 2 chromosomes. In this study, we identified and characterized the function of TaCSN5 in response to infection by the leaf rust pathogen. Down-regulation of all three TaCSN5 homeologues or mutations in the homeologues on chromosomes 2A or 2D resulted in significantly enhanced resistance to leaf rust. Enhanced leaf rust resistance corresponded to a seven-fold increase in PR1 (pathogenesis-related gene 1) expression. Collectively, the data indicate that the wheat COP9 subunit 5-like gene acts as a negative regulator of wheat leaf rust resistance.