Silencing PHOSPHOENOLPYRUVATE CARBOXYLASE1 in the Obligate Crassulacean Acid Metabolism Species Kalanchoë laxiflora causes Reversion to C3-like Metabolism and Amplifies Rhythmicity in a Subset of Core Circadian Clock Genes



Boxall, Susanna ORCID: 0000-0002-8753-101X, Kadu, Nirja, Dever, Louisa, Kneřová, Jana, Waller, Jade, Gould, Peter and Hartwell, James
(2019) Silencing PHOSPHOENOLPYRUVATE CARBOXYLASE1 in the Obligate Crassulacean Acid Metabolism Species Kalanchoë laxiflora causes Reversion to C3-like Metabolism and Amplifies Rhythmicity in a Subset of Core Circadian Clock Genes.

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Abstract

ABSTRACT Unlike C 3 plants, Crassulacean acid metabolism (CAM) plants fix CO 2 in the dark using phosphoenolpyruvate carboxylase (PPC; EC 4.1.1.31). PPC combines PEP with CO 2 (as HCO 3 − ), forming oxaloacetate that is rapidly converted to malate, leading to vacuolar malic acid accumulation that peaks phased to dawn. In the light period, malate decarboxylation concentrates CO 2 around RuBisCO for secondary fixation. CAM mutants lacking PPC have not been described. Here, RNAi was employed to silence CAM isogene PPC1 in Kalanchoë laxiflora . Line rPPC1-B lacked PPC1 transcripts, PPC activity, dark period CO 2 fixation, and nocturnal malate accumulation. Light period stomatal closure was also perturbed, and the plants displayed reduced but detectable dark period stomatal conductance, and arrhythmia of the CAM CO 2 fixation circadian rhythm under constant light and temperature (LL) free-running conditions. By contrast, the rhythm of delayed fluorescence was enhanced in plants lacking PPC1 . Furthermore, a subset of gene transcripts within the central circadian oscillator were up-regulated and oscillated robustly. The regulation guard cell genes involved controlling stomatal movements was also altered in rPPC1-B . This provided direct evidence that altered regulatory patterns of key guard cell signaling genes are linked with the characteristic inverse pattern of stomatal opening and closing during CAM.

Item Type: Article
Depositing User: Symplectic Admin
Date Deposited: 28 Oct 2019 09:22
Last Modified: 07 Jul 2021 11:24
DOI: 10.1101/684050
URI: https://livrepository.liverpool.ac.uk/id/eprint/3059532