RESUMEN
Single-cell C4 photosynthesis (SCC4) in terrestrial plants without Kranz anatomy involves three steps: initial CO2 fixation in the cytosol, CO2 release in mitochondria, and a second CO2 fixation in central chloroplasts. Here, we investigated how the large number of mechanisms underlying these processes, which occur in three different compartments, are orchestrated in a coordinated manner to establish the C4 pathway in Bienertia sinuspersici, a SCC4 plant. Leaves were subjected to transcriptome analysis at three different developmental stages. Functional enrichment analysis revealed that SCC4 cycle genes are coexpressed with genes regulating cyclic electron flow and amino/organic acid metabolism, two key processes required for the production of energy molecules in C3 plants. Comparative gene expression profiling of B. sinuspersici and three other species (Suaeda aralocaspica, Amaranthus hypochondriacus, and Arabidopsis thaliana) showed that the direction of metabolic flux was determined via an alteration in energy supply in peripheral chloroplasts and mitochondria via regulation of gene expression in the direction of the C4 cycle. Based on these results, we propose that the redox homeostasis of energy molecules via energy metabolism regulation is key to the establishment of the SCC4 pathway in B. sinuspersici.
RESUMEN
Incorporating C4 photosynthetic traits into C3 crops is a rational approach for sustaining future demands for crop productivity. Using classical plant breeding, engineering this complex trait is unlikely to achieve its target. Therefore, it is critical and timely to implement novel biotechnological crop improvement strategies to accomplish this goal. However, a fundamental understanding of C3 , C4 , and C3 -C4 intermediate metabolism is crucial for the targeted use of biotechnological tools. This review assesses recent progress towards engineering C4 photosynthetic traits in C3 crops. We also discuss lessons learned from successes and failures of recent genetic engineering attempts in C3 crops, highlighting the pros and cons of using rice as a model plant for short-, medium- and long-term goals of genetic engineering. This review provides an integrated approach towards engineering improved photosynthetic efficiency in C3 crops for sustaining food, fibre and fuel production around the globe.
Asunto(s)
Oryza , Fitomejoramiento , Producción de Cultivos , Productos Agrícolas/genética , Oryza/genética , Fotosíntesis/genética , Hojas de la Planta/metabolismoRESUMEN
Most nucleus-encoded chloroplast proteins rely on an N-terminal transit peptide (TP) as a post-translational sorting signal for directing them to the organelle. Although Toc159 is known to be a receptor for specific preprotein TPs at the chloroplast surface, the mechanism for its own targeting and integration into the chloroplast outer membrane is not completely understood. In a previous study, we identified a novel TP-like sorting signal at the C-terminus (CT) of a Toc159 homolog from the single-cell C4 species, Bienertia sinuspersici. In the current study, we have extended our understanding of the sorting signal using transient expression of fluorescently-tagged fusion proteins of variable-length, and with truncated and swapped versions of the CT. As was shown in the earlier study, the 56 residues of the CT contain crucial sorting information for reversible interaction of the receptor with the chloroplast envelope. Extension of this region to 100 residues in the current study stabilized the interaction via membrane integration, as demonstrated by more prominent plastid-associated signals and resistance of the fusion protein to alkaline extraction. Despite a high degree of sequence similarity, the plastid localization signals of the equivalent CT regions of Arabidopsis thaliana Toc159 homologs were not as strong as that of the B. sinuspersici counterparts. Together with computational and circular dichroism analyses of the CT domain structures, our data provide insights into the critical elements of the CT for the efficient targeting and anchorage of Toc159 receptors to the dimorphic chloroplasts in the single-cell C4 species.