Document Detail


Transgenic perturbation of the decarboxylation phase of Crassulacean acid metabolism alters physiology and metabolism but has only a small effect on growth.
MedLine Citation:
PMID:  25378692     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
Mitochondrial NAD-malic enzyme (NAD-ME) and/or cytosolic/ plastidic NADP-ME combined with cytosolic/ plastidic pyruvate orthophosphate dikinase (PPDK) catalyse two key steps during light-period malate decarboxylation that underpins secondary CO2 fixation in some Crassulacean acid metabolism (CAM) species. We report the generation and phenotypic characterisation of transgenic RNAi lines of the obligate CAM species Kalanchoë fedtschenkoi with reduced activities of NAD-ME or PPDK. Transgenic line rNAD-ME1 had 8 %, and rPPDK1 had 5 % of the wild type level of activity, and showed dramatic changes in the light-dark cycle of CAM CO2 fixation. In well-watered conditions, these lines fixed all of their CO2 in the light; they thus performed C3 photosynthesis. The alternative malate decarboxylase, NADP-ME, did not appear to compensate for the reduction in NAD-ME, suggesting NAD-ME was the key decarboxylase for CAM. The activity of other CAM enzymes was reduced as a consequence of knocking out either NAD-ME or PPDK activity, particularly phosphoenolpyruvate carboxylase (PPC) and PPDK in rNAD-ME1. Furthermore, the circadian clock controlled phosphorylation of PPC in the dark was reduced in both lines, especially in rNAD-ME1. This had the consequence that circadian rhythms of PPC phosphorylation, PPC kinase (PPCK) transcript levels and activity, and the classic circadian rhythm of CAM CO2 fixation were lost, or dampened towards arrhythmia, under constant light and temperature conditions. Surprisingly, oscillations in the transcript abundance of core circadian clock genes also became arrhythmic in the rNAD-ME1 line, suggesting that perturbing CAM in K. fedtschenkoi feeds back to perturb the central circadian clock.
Authors:
Louisa V Dever; Susanna F Boxall; Jana Kneřová; James Hartwell
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2014-11-5
Journal Detail:
Title:  Plant physiology     Volume:  -     ISSN:  1532-2548     ISO Abbreviation:  Plant Physiol.     Publication Date:  2014 Nov 
Date Detail:
Created Date:  2014-11-7     Completed Date:  -     Revised Date:  2014-11-8    
Medline Journal Info:
Nlm Unique ID:  0401224     Medline TA:  Plant Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Copyright Information:
Copyright © 2014, American Society of Plant Biologists.
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