ALTERATIONS IN TRANSCRIPTION AND TRANSLATION IN COMPATIBLE MAIZE-HELMINTHOSPORIUM MAYDIS INTERACTION (PROTEIN SYNTHESIS, RIBOSOME-ASSOCIATED, RNA POLYMERASE)
Abstract
Progress has been made in the study of incompatible interactions of host-pathogen systems, but little is known about the mechanism of compatible host-pathogen interactions. Changes in the level of transcription and translation at an early stage of compatible maize-fungal pathogen interactions were studied. Seven-day-old W64A maize seedlings were inoculated with Helminthosporium maydis, other pathogens, and nonpathogens, or treated with heat or paraquat. Leaves were harvested at intervals from 3 to 48 h after inoculation, and examined for protein synthetic machinery (polysomes) and nuclear RNA polymerase II. Protein synthesis was studied in both in vivo and in vitro translational systems; the latter used the wheat germ cell-free system. The early biochemical events observed in the compatible maize-H. maydis interaction include: (a) the induced synthesis of a 90K dalton protein in vivo and in vitro; (b) a polysome shift and diminuation of four specific proteins (23, 24, 25, and 33K daltons) synthesized in vitro; and (c) a gradual decrease in translational efficiency of polysomes. Similar alterations were also observed in maize inoculated with other pathogens, but not with nonpathogens. Diminuation of the four specific proteins occurred only in disease interactions, whereas the induction of a 90K protein occurred also in heat shocked or paraquat treated maize seedlings. Alterations of ribosome-associated proteins (RAPs), i.e. an increase of 90K and a 31K dalton proteins, were observed in W64A maize inoculated with H. maydis or other pathogens, but not with a nonpathogen. The 90K RAP was also induced by heat shock or paraquat treatments. The 90K RAP appeared to be associated with 40S ribosomal subunits. Therefore, the 90K RAP, as with ribosome-associated initiation factors, may play a role in the regulation of protein synthesis during initiation of the compatible maize-H. maydis interaction. The RNA polymerase II isolated from healthy or H. maydis-inoculated leaves were different based on (alpha)-amanitin sensitivity, Mn('++) preference, temperature optimum, heat sensitivity and template preference; although their Mg('++) and Mn('++) optima, pH optimum and kinetics of UMP incorporation were similar. These alterations, especially the change of template preference, suggest a modification of the transcriptive specificity of RNA polymerase II in a compatible maize-H. maydis interaction.
Degree
Ph.D.
Subject Area
Plant pathology
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