Identification and characterization of a serine protease from wheat leaves
Citation
Fan, T., Bykova, N.V., Rampitsch, C., Xing, T. (2016). Identification and characterization of a serine protease from wheat leaves. European Journal of Plant Pathology, [online] 146(2), 293-304. http://dx.doi.org/10.1007/s10658-016-0914-x
Plain language summary
When plants are infected by fungi, they produce a lot of proteins to try and defend themselves against attack. This is part of their immune response. One class of proteins commonly seen are proteases – enzymes which can destroy other proteins by breaking them down. Here we describe the discovery of a protease from wheat leaves that have been attacked by the fungus that causes leaf rust. Since these proteases are quite powerful, they are only produced in very small amounts, and this makes them hard to find. We were able to classify the one we found as a serine protease based on some of its biochemical properties that we could test. We are still not entirely sure of the full role of this protease in the wheat immune response but we speculate that it has important and diverse roles in regulating normal wheat leaf growth and development, senescence, and pathogen.
Abstract
A putative serine protease with a potential role in the plant biotic and abiotic stress response was purified from wheat leaf apoplastic fluid and partially characterized. Following two-dimensional electrophoresis a protein of Mr = 75 k and a pI of 4.2 to 4.5 was observed. This protein displayed in-gel protease activity and was specifically inhibited by phenylmethanesulfonyl fluoride and partially inhibited by Ca2+ and Zn2+, but not by E-64 or leupeptin. An internal tryptic fragment of 13 amino acids was identified by MALDI QqTOF MS/MS, and this peptide showed a high level of homology (85–100 % identity) to a highly conserved region of known plant subtilisin-like proteases. We demonstrated that the protease activity increased until a late stage of wheat leaf development and increased in response to heat shock. In both cases Rubisco large subunit was degraded with time. Protease activity was also increased during biotic stress. Leaves challenged with leaf rust (Puccinia triticina), showed an approximately three fold increase in protease activity during an incompatible interaction, compared to activity in mock-inoculated leaves and to leaves in a compatible leaf rust interaction. These results suggest that the expression of this serine protease could be involved in the defense response against both abiotic and biotic stresses.