Potential protein biomarkers of QX disease resistance in selectively bred Sydney Rock Oysters

The Sydney Rock Oyster (SRO) (Saccostrea glomerata) industry of Australia has faced repeated challenges from both anthropogenic and natural threats. One important factor that has caused substantial loss to the industry is a protozoan-borne disease known as QX disease. To ensure sustainable production of SRO, a selective breeding programme has been employed to develop a line of QX disease resistant oysters. In this study, we have performed a label-free quantitative shotgun proteomic analysis of control and selectively bred SRO to identify potential protein biomarkers of disease resistance. We extracted proteins from the gills of two different oyster populations (QX resistant and non-selected wild type, n = 20 per population) sampled at two different time points, to gain insights into disease resistance during the oyster growth cycle. The current study identifies a pattern of protein changes over the two time points, which includes some results coincident with previous published reports, as well as some novel findings. We have identified 21 differentially expressed proteins between the two lines of oysters at the first time point, and 22 differentially expressed proteins at the second time point. These include proteins involved in cytoskeletal remodelling, immune response, energy metabolism, and numerous other functions. In particular, we report the increased abundance in selectively bred oysters of High Mobility Group Box 1 protein (HMGB1), which has been reported to play an important role in the oyster immune response. In addition, we have identified changes in abundance levels of Major Vault Protein (MVP), Histone H2A, dscam, Ras related Rab11B, proteasome subunits, and numerous other proteins that have previously been reported to be relevant in the context of molluscan stress responses. These proteins have potential for use as disease resistance biomarkers within a population, and also help build our understanding of the biological phenomena underlying selection for disease resistance.