Photosynthetic Gene Expression in Amaranth, an NAD-ME Type C4 Dicot

Abstract

Post-transcriptional regulation determines initial C4 gene expression patterns in developing leaves of Amaranthus hypochondriacus, an NAD-ME type C4 dicot. RuBPCase, PEPCase, and PPdK mRNAs are abundant in meristems and in leaf primordia, but are utilised only during specific developmental stages. While each enzyme shows independent patterns of initial mRNA and polypeptide accumulation, cell-specific localisation of the polypeptides occurs prior to cell-specific localisation of the mRNAs. In mature three-coloured leaves of A. tricolor, loss of photosynthetic activity correlates with reductions in the transcription rates of some plastid-encoded genes, reduction and loss of coordination in the translation of RuBPCase polypeptides, and loss of cell-specific accumulation of RuBPCase mRNAs (but not the polypeptides). The mitochondrial NAD-dependent malic enzyme (NAD-ME) provides an example of a basic metabolic enzyme that has acquired specialised gene expression patterns allowing it to function in the C4 pathway. NAD-ME occurs preferentially in photosynthetic tissues, and is specific to bundle sheath cells throughout development. NAD-ME synthesis is regulated by light and development at transcriptional and post-transcriptional levels. The findings summarised here indicate that C4 genes are independently regulated by multiple control mechanisms in response to developmental, environmental, and metabolic signals.

Untranslated Regions from C4 Amaranth AhRbcS1 mRNAs Confer Translational Enhancement and Preferential Bundle Sheath Cell Expression in Transgenic C4Flaveria bidentis

“…Many aspects of Rubisco gene expression are common to both C 3 and C 4 plants, the most notable of these being expression primarily in photosynthetic leaves and cotyledons, and regulation by light within these tissues (Gilmartin et al, 1990;Cory, 1994;Viret et al, 1994;Berry et al, 1997). In addition, overall levels of RbcS and rbcL gene expression are often controlled by development (Wanner and Gruissem, 1991;Hensel et al, 1993;Ramsperger et al, 1996), cell and tissue type (Furbank and Taylor, 1995;Sheen, 1999), and photosynthetic metabolism (Sheen, 1990;Krapp et al, 1993;Wang et al, 1993a;McCormac et al, 1997).…”

“…In the C 4 dicot amaranth, posttranscriptional regulation contributes substantially to the establishment and maintenance of bs-specific RbcS and rbcL gene expression during C 4 leaf development (Boinski et al, 1993;Ramsperger et al, 1996) and in response to changes in photosynthetic activity . Posttranscriptional control may be a property of Rubisco expression in many C 4 plants; such regulation has been shown to be involved with determination of bs cell specificity in C 4 monocots as well as C 4 dicots (Schaffner and Sheen, 1991;Bansal et al, 1992, Kubicki et al, 1994Viret et al, 1994;Roth et al, 1996;Berry et al, 1997;Sheen, 1999).…”

“…One set of CO 2 fixation enzymes, including Rubisco, accumulates only in leaf bundle sheath (bs) cells, while others, such as phosphoenolpyruvate carboxylase, are produced only in leaf mesophyll (mp) cells. In all C 4 species, the various photosynthetic enzymes are regulated independently (Furbank and Taylor, 1995;Berry et al, 1997;Sheen, 1999) yet share many characteristic gene expression patterns required for their function in CO 2 fixation. These include very high levels of expression, localization to specific cell types within leaves or other photosynthetic tissues, and regulation by light.…”

“…These include very high levels of expression, localization to specific cell types within leaves or other photosynthetic tissues, and regulation by light. For many C 4 genes, including those encoding the Rubisco small subunit (SSU; encoded by nuclear RbcS genes) and large subunit (encoded by plastid rbcL genes), posttranscriptional control processes have been implicated in one or more aspects of their regulation (Furbank and Taylor, 1995;Berry et al, 1997;Sheen, 1999).…”

Expression Profiles of <i>psbA, ALS, EPSPS</i>, and Other Chloroplastic Genes in Response to PSII-, ALS-, and EPSPS-Inhibitor Treatments in <i>Kochia scoparia</i>

“…The expression of Rubisco is dependent on various factors such as light [47] [48], cell and tissue type [49] [50], efficiency of photosynthetic machinery [51], phytohormone and nutrient levels [52] [53], and plant developmental stage [54]. Rubisco consists of two subunits (large and small), encoded by two separate genes (chloroplastic large subunit, LSU and nuclear small subunit, SSU) [55].…”