Pretranslational control of the levels of glyoxysomal protein gene expression by the embryonic axis in maize

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Abstract
Previous studies showed that the expression of catalase‐2 (CAT‐2) and other glyoxysomal proteins is independently controlled in the scutella of intact maize seedlings. In this study, removal of the embryonic axis prior to seed imbibition dramatically decreased the amounts of all but two of the 19 immunologically detectable glyoxysomal proteins in the scutellum, including CAT‐2. The temporal expression profile of CAT‐2 was also altered. Removal of the axis after seeds were fully imbibed (24 hr) had little effect on the subsequent pattern of expression of CAT‐2. The effect of axis removal was specific for glyoxysomal enzymes and caused relatively little change in the population of stainable scutellar proteins. In vitro translation studies and nucleic acid hybridization with a gene‐specific cloned probe (for Cat2) revealed that the mRNA levels for glyoxysomal proteins were sharply lowered by axis removal. This study provides evidence that a signal may be released from the embryonic axis during imbibition, leading to the expression of a set of glyoxysomal enzymes by enhancing either the transcription of their genes or transcript stability.