PLANT PHYSIOLOGY , Vol 112, Issue 2 537-547, Copyright © 1996 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Tomato E8 Gene Influences Ethylene Biosynthesis in Fruit but Not in Flowers
M. L. Kneissl and J. Deikman
Department of Biology, 208 Mueller Laboratory, Biotechnology Institute, and Intercollege Graduate Program in Plant Physiology, Pennsylvania State University, University Park, Pennsylvania 16802
We investigated the function of the tomato (Lycopersicon esculentum) E8
gene. Previous experiments in which antisense suppression of E8 was used
suggested that the E8 protein has a negative effect on ethylene evolution
in fruit. E8 is expressed in flowers as well as in fruit, and its
expression is high in anthers. We introduced a cauliflower mosaic virus
35S-E8 gene into tomato plants and obtained plants with overexpression of
E8 and plants in which E8 expression was suppressed due to co-suppression.
Overexpression of E8 in unripe fruit did not affect the level of ethylene
evolution during fruit ripening; however, reduction of E8 protein by
cosuppression did lead to elevated levels during ripening. Levels for
ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC), and ACC oxidase mRNA
were increased approximately 7-fold in fruit of plants with reduced E8
protein. Levels of ACC synthase 2 mRNA were increased 2.5-fold, and ACC
synthase 4 mRNA was not affected. Reduction of E8 protein in anthers did
not affect the accumulation of ACC or of mRNAs encoding enzymes involved in
ethylene biosynthesis. Our results suggest that the product of the E8
reaction participates in feedback regulation of ethylene biosynthesis
during fruit ripening.
