Record ID No. |
1520 |
Author(s) |
Floss, DS; Schliemann, W; Schmidt, J; Strack, D; Walter MH. , 2008 |
Affiliation |
Leibniz Inst Pflanzenbiochem, Abt Sekundarstoffwechsel, D-06120 Halle, GERMANY |
Title |
RNA Interference-Mediated Repression of MtCCD1 in Mycorrhizal Roots of Medicago truncatula Causes Accumulation of C-27 Apocarotenoids, Shedding Light on the Functional Role of CCD1 |
Source. Vol.(no):Page |
Plant Physiology, 148(3): 1267-1282 |
Categories |
Arbuscular Mycorrhiza |
Subjects |
Biochemistry |
Sub-subjects |
Miscellaneous |
Country |
Germany, Europe |
Abstracts |
Tailoring carotenoids by plant carotenoid cleavage dioxygenases (CCDs) generates various bioactive apocarotenoids. Recombinant CCD1 has been shown to catalyze symmetrical cleavage of C 40 carotenoid substrates at 9,10 and 9', 10' positions. The actual substrate(s) of the enzyme in planta, however, is still unknown. In this study, we have carried out RNA interference (RNAi)-mediated repression of a Medicago truncatula CCD1 gene in hairy roots colonized by the arbuscular mycorrhizal (AM) fungus Glomus intraradices. As a consequence, the normal AM-mediated accumulation of apocarotenoids (C 13 cyclohexenone and C 14 mycorradicin derivatives) was differentially modified. Mycorradicin derivatives were strongly reduced to 3% to 6% of the controls, while the cyclohexenone derivatives were only reduced to 30% to 47%. Concomitantly, a yellow-orange color appeared in RNAi roots. Based on ultraviolet light spectra and mass spectrometry analyses, the new compounds are C 27 apocarotenoic acid derivatives. These metabolic alterations did not lead to major changes in molecular markers of the AM symbiosis, although a moderate shift to more degenerating arbuscules was observed in RNAi roots. The unexpected outcome of the RNAi approach suggests C 27 apocarotenoids as the major substrates of CCD1 in mycorrhizal root cells. Moreover, literature data implicate C 27 apocarotenoid cleavage as the general functional role of CCD1 in planta. A revised scheme of plant carotenoid cleavage in two consecutive steps is proposed, in which CCD1 catalyzes only the second step in the cytosol (C-27 -> C-14 + C-13), while the first step (C-40 -> C-27 + C-13) may be catalyzed by CCD7 and/or CCD4 inside plastids. |