Fungal-induced synthesis of pathogenesis-related proteins in germinating maize embryos

Abstract

Changes in the pattern of protein synthesis in germinating maize embryos have been examined after infection with the fungus Fusarium moniliforme. Two-dimensional gel electrophoresis was used to compare changes in proteins formed in vivo and in an in vitro translation system, from non-infected and F. moniliforme-infected embryos. Moreover, the protein patterns obtained using acidic or neutral extraction buffers have been compared. In vivo labelling experiments show that infection with F. moniliforme results in the induction of the synthesis of two major acid-soluble polypeptides with mol. wts of 24 and 17 kDa and with highly basic isoelectric points. Induction of these basic proteins is followed by their accumulation in tissues of the infected embryos. In addition to this, the analysis of the proteins formed during a 3 h pulse labelling with 35S-methionine reveals the synthesis of a group of proteins with low mol. wts (below 30 kDa) and acidic isoelectric points in response to fungal infection or treatment with fungal elicitors. Translation of mRNAs obtained from uninfected and F. moniliforme-infected embryos in vitro confirms the accumulation of mRNAs coding for acidic low mol. wt proteins on infection. However, contrary to the behaviour of the fungal-induced basic proteins, the fungalinduced acidic proteins do not accumulate in embryo tissues during germination. We conclude that expression and/or accumulation of basic and acidic pathogenesis-related proteins in response to fungal infection are differentially regulated during germination of maize embryos. Mechanisms for the control of the expression of defence-related genes, other than transcriptional activation, may play an important role in defence responses against fungal infection during seed germination.