Transgenic Perturbation of the Decarboxylation Phase of Crassulacean Acid Metabolism Alters Physiology and Metabolism But Has Only a Small Effect on Growth

Nov 8, 2014Plant physiology

Changing a key step in nighttime acid metabolism affects plant function and chemistry but only slightly changes growth

AI simplified

Circadian Biology on OpenScience ↗PubMed ↗DOI ↗

Abstract

Transgenic lines of Kalanchoë fedtschenkoi with reduced NAD-malic enzyme activity exhibited only 8% of the wild-type activity.

Reduced NAD-malic enzyme activity resulted in the transgenic lines performing C(3) photosynthesis instead of CAM.
NADP-malic enzyme did not compensate for the loss of NAD-malic enzyme, indicating its critical role in CAM.
Knocking out NAD-malic enzyme or PPDK activity led to decreased activity of other CAM enzymes, particularly phosphoenolpyruvate carboxylase.
Phosphorylation of phosphoenolpyruvate carboxylase, controlled by the circadian clock, was diminished in both transgenic lines.
Circadian rhythms of key processes related to CAM and core circadian clock genes became disrupted in the rNAD-ME1 line.

AI simplified

Mitochondrial NAD-malic enzyme (ME) and/or cytosolic/plastidic NADP-ME combined with the cytosolic/plastidic pyruvate orthophosphate dikinase (PPDK) catalyze two key steps during light-period malate decarboxylation that underpin secondary CO(2) fixation in some Crassulacean acid metabolism (CAM) species. We report the generation and phenotypic characterization of transgenic RNA interference 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 CO(2) fixation. In well-watered conditions, these lines fixed all of their CO(2) in the light; they thus performed C(3) photosynthesis. The alternative malate decarboxylase, NADP-ME, did not appear to compensate for the reduction in NAD-ME, suggesting that 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 transcript levels and activity, and the classic circadian rhythm of CAM CO(2) fixation were lost, or dampened toward 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.

Full Text

Full text is available at the source.

View full text ↗

Transgenic Perturbation of the Decarboxylation Phase of Crassulacean Acid Metabolism Alters Physiology and Metabolism But Has Only a Small Effect on Growth

Abstract

Full Text

You found one interesting study. We’ll send the next 7.

what lands in your inbox each week:

Recent issues from the circadian biology brief

Abstract

Full Text

Related papers

You found one interesting study. We’ll send the next 7.

what lands in your inbox each week:

Recent issues from the circadian biology brief