PARENT SESSION
Posters P7D Chloroplast factories and transformation. Abstracts (754-758)

Temperature-sensitive mechanism regulating post-translational stability of a plastidial -3 fatty acid desaturase (FAD8) in Arabidopsis. Osamu Matsuda^*,1, Hikaru Sakamoto¹, Tadafumi Hashimoto¹, Koh Iba¹, ¹ Department of Biology, Fukuoka, Japan

ABSTRACT- Trienoic fatty acids (TAs) are the major constituents in the membrane lipids of plant cells. In Arabidopsis, two plastidial isozymes of the -3 fatty acid desaturase, FAD7 and FAD8, provide the major contribution to the production of TAs in the leaf tissues. Despite a high degree of structural relatedness, activity of these two isozymes is regulated differentially in response to temperature. Of the two plastidial isozymes, the FAD8 was originally identified as a temperature-sensitive enzyme. To dissect the mechanisms involved in the temperature-sensitive switchover of the FAD8 desaturase activity, a series of FAD7-FAD8 chimeric genes, each encoding a functional plastidial -3 desaturase, either with or without a c-Myc epitope tag, were introduced into the fad7fad8 double mutant. Expression of each chimeric gene in response to temperature was assayed by Northern and Western blot analyses, and by examining the complementation of the fatty acid composition. All transformants harboring a chimeric gene containing the FAD8-derived C-terminal coding region displayed temperature-dependent change of the leaf TA level as in the transgenic lines complemented with the native form of the FAD8 gene. This was accompanied by a change in the amount of the -3 desaturase protein, but not necessarily by a change in the transcript level. Analysis of the decay of c-Myc-tagged products after inhibition of protein synthesis revealed that C-terminal structure of the FAD8 desaturase acts in an autoregulatory fashion to destabilize the protein at high temperature. Although special attention has been focused on the regulation at the transcriptional level, our results rather implicated the post-translational stability of the FAD8 desaturase in the temperature-dependent change of the leaf TA level.

KEY WORDS: trienoic fatty acids, omega-3 fatty acid desaturase, temperature, Arabidopsis