Analysis of apoplastic proteins expressed during net form net blotch of barley

The net form net blotch (NFNB) is a significant disease of barley. Its causal agent, Pyrenophora teres f. teres (PTT), has an important economic impact on yield and grain quality globally. However, the molecular interaction between PTT and barley is not fully understood. The plant–pathogen encounter comprises the secretion of diverse molecules involved in plant defence, including pathogenicity-related proteins, and fungal attack, such as proteinaceous toxins called effectors. The forefront of the molecular crosstalk between plant and fungus is the space between plant cells or apoplast. To explore the suitability of studying apoplastic proteins to assist understanding the host–pathogen interaction, a mass spectrometry-based proteomics technique was used to profile apoplastic protein differences in control and NFNB-infected leaves in a susceptible cultivar. The analysis revealed 1130 barley proteins, of which 140 were found to be significantly differentially expressed. This paper presents an overview of the major protein changes induced in the barley apoplast and discusses the involvement of individual proteins in defence and disease development. Our results suggest that the fungus may be hijacking defence signalling pathways. This investigation provides the first in vivo proteomics data for a NFNB–barley interaction, setting a background for further studies.