Reduced Expression of Aconitase Results in an Enhanced Rate of Photosynthesis and Marked Shifts in Carbon Partitioning in Illuminated Leaves of Wild Species Tomato

Abstract

Wild species tomato (Lycopersicon pennellii) plants bearing a genetic lesion in the gene encoding aconitase (Aco-1; aconitate hydratase EC 4.2.1.3) were characterized at molecular and biochemical levels. The genetic basis of this lesion was revealed by cloning the wild-type and mutant alleles. The mutation resulted in lowered expression of the Aco-1 transcript and lowered levels of both cytosolic and mitochondrial aconitase protein and activity. After in silico analysis, we concluded that in the absence of a recognizable target sequence, the best explanation for the dual location of this protein is inefficient targeting. Biochemical analysis of leaves of the Aco-1 accession suggested that they exhibited a restricted flux through the Krebs cycle and reduced levels of Krebs cycle intermediates but were characterized by elevated adenylate levels and an enhanced rate of CO 2 assimilation. Furthermore, the analysis of both steady-state metabolite levels and metabolic fluxes revealed that this accession also exhibited elevated rates of photosynthetic Suc synthesis and a corresponding increase in fruit yield. Therefore, we conclude that the Krebs cycle normally competes with the Suc synthetic pathway for carbon but is not essential for the supply of energy to fuel the operation of this pathway.

The iron-responsive element (IRE)/iron-regulatory protein 1 (IRP1)–cytosolic aconitase iron-regulatory switch does not operate in plants

“…It is not the case in Saccharomyces cerevisiae, in which a unique gene encodes both mitochondrial and cytosolic ACOs [38,39]. In plants, several reports indicate that, as in yeast, both mitochondrial and cytosolic ACOs are encoded by the same genes, suggesting a dual targeting of the proteins [40][41][42]. Therefore the question we had to address was whether or not the three identified ACOs were targeted to the cytosol.…”

“…The relative contribution of each ACO isoform to the mitochondrial and cytosolic ACO activities, to the metabolism [42], to the regulation of oxidative stress and to the establishment of defence against pathogens [20,45] could be studied with the loss-of-function mutants.…”

RNA Interference of LIN5 in Tomato Confirms Its Role in Controlling Brix Content, Uncovers the Influence of Sugars on the Levels of Fruit Hormones, and Demonstrates the Importance of Sucrose Cleavage for Normal Fruit Development and Fertility

“…Plants were handled as described in the literature (Carrari et al, 2003;Nunes-Nesi et al, 2005). For the drought stress treatments, well-watered 7-week-old flowering tomato plants were used.…”

A Nuclear Gene Encoding the Iron-Sulfur Subunit of Mitochondrial Complex II Is Regulated by B3 Domain Transcription Factors during Seed Development in Arabidopsis

“…A wide range of mutant, antisense, or silenced plants with deficient expression of enzymes from the TCA cycle have been described, including citrate synthase (Landschü tze et al, 1995), aconitase (Carrari et al, 2003), malate dehydrogenase (Nunes-Nesi et al, 2005), fumarase , succinyl CoA ligase (Studart-Guimarães et al, 2007), and NAD + -dependent isocitrate dehydrogenase (Lemaitre et al, 2007). These studies have shown that modifications in the TCA cycle can modulate photosynthetic performance and, in the case of potato (Solanum tuberosum) citrate synthase, lead to a specific disintegration of the ovary tissues of flower.…”