Leaf Development in the Single-Cell C₄ System in Bienertia sinuspersici: Expression of Genes and Peptide Levels for C₄ Metabolism in Relation to Chlorenchyma Structure under Different Light Conditions

Abstract

Bienertia sinuspersici performs C 4 photosynthesis in individual chlorenchyma cells by the development of two cytoplasmic domains (peripheral and central) with dimorphic chloroplasts, an arrangement that spatially separates the fixation of atmospheric CO 2 into C 4 acids and the donation of CO 2 from C 4 acids to Rubisco in the C 3 cycle. In association with the formation of these cytoplasmic domains during leaf maturation, developmental stages were analyzed for the expression of a number of photosynthetic genes, including Rubisco small and large subunits and key enzymes of the C 4 cycle. Early in development, Rubisco subunits and Gly decarboxylase and Ser hydroxymethyltransferase of the glycolate pathway accumulated more rapidly than enzymes associated with the C 4 cycle. The levels of pyruvate,Pi dikinase and phosphoenolpyruvate carboxylase were especially low until spatial cytoplasmic domains developed and leaves reached maturity, indicating a developmental transition toward C 4 photosynthesis. In most cases, there was a correlation between the accumulation of mRNA transcripts and the respective peptides, indicating at least partial control of the development of photosynthesis at the transcriptional level. During growth under moderate light, when branches containing mature leaves were enclosed in darkness for 1 month, spatial domains were maintained and there was high retention of a number of photosynthetic peptides, including Rubisco subunits and pyruvate,Pi dikinase, despite a reduction in transcript levels. When plants were transferred from moderate to low light conditions for 1 month, there was a striking shift of the central cytoplasmic compartment toward the periphery of chlorenchyma cells; the mature leaves showed strong acclimation with a shade-type photosynthetic response to light while retaining C 4 features indicative of low photorespiration. These results indicate a progressive development of C 4 photosynthesis with differences in the control mechanisms for the expression of photosynthetic genes and peptide synthesis during leaf maturation and in response to light conditions.

Resolving the Compartmentation and Function of C4 Photosynthesis in the Single-Cell C4 Species Bienertia sinuspersici

“…An Asp-Ala shuttle is proposed, as we found no evidence for OAA being converted to MA by the P-CP. Additionally, we observed localization of Ala-AT and c-Asp-AT to the cytoplasm and mAsp-AT to the mitochondria, and these enzymes increase during development of the C 4 system in B. sinuspersici (Lara et al, 2008), which provides further evidence for the proposed pathway. Furthermore, Park et al (2010) recently found evidence for the occurrence of all 10 enzymes required to support an Asp-Ala C 4 cycle shuttle in B. sinuspersici in a proteomics study.…”

Structural changes in the vacuole and cytoskeleton are key to development of the two cytoplasmic domains supporting single-cell C4 photosynthesis in Bienertia sinuspersici

“…A study on Bienertia cycloptera by transmission electron microscopy showed chlorenchyma cells undergo transition from a C 3 default mode in young cells (one type of chloroplast, all contain some Rubisco) to a C 4 form in mature cells having spatial cytoplasmic domains (with dimorphic chloroplasts) which are connected by cytoplasmic channels traversing the vacuole (Voznesenskaya et al 2005). In addition, studies on Bienertia species show a biochemical transition with Rubisco expressed early followed by increased expression of enzymes of the C 4 cycle, including PPDK and PEPC, later in leaf development (Voznesenskaya et al 2005;Lara et al 2008).…”

C4 Cycles: Past, Present, and Future Research on C4 Photosynthesis

“…In each of the two compartments, chloroplasts accumulate a distinct complement of photosynthetic enzymes with the peripheral/distal chloroplasts analogous to M cell chloroplasts of the Kranz system and the central/proximal chloroplasts analogous to the BS cell chloroplasts. Crucially, this dimorphism is not apparent early in development in that a monomorphic C 3 chloroplast state develops by default and the C 4 pattern is induced by later developmental cues (Voznesenskaya et al, 2005;Lara et al, 2008).…”