C4 Photosynthesis: Mechanism and Regulation

Furbank, Robert T.; Hatch, M.D.; Jenkins, Colin L. D.

doi:10.1007/0-306-48137-5_18

Cited by 40 publications

(31 citation statements)

References 106 publications

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“…To date, evidence indicates that, during the evolution of C 4 photosynthesis, multiple levels of regulation have been utilized and coordinated to achieve the cell-specific gene expression patterns required for the function of this specialized CO 2 fixation pathway. Control of C 4 gene expression at the level of transcription has been implicated in many studies (Nelson and Langdale, 1992;Furbank and Taylor, 1995;Berry et al, 1997;Sheen, 1999;Furbank et al, 2000;Matsuoka et al, 2001, Leegood, 2002Shoichi and Burnell, 2003;Gowik et al, 2004). Photosynthetic promoters linked to reporter genes have reproduced some level of cell type-specific or tissue-specific expression patterns when these are expressed in C 4 plants, although in some cases only partial bs or mp cell specificity has been obtained.…”

Section: Discussionmentioning

confidence: 99%

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

et al. 2004

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Many aspects of photosynthetic gene expression are posttranscriptionally regulated in C4 plants. To determine if RbcS mRNA untranslated regions (UTRs) in themselves could confer any characteristic C4 expression patterns, 5′- and 3′-UTRs of AhRbcS1 mRNA from the C4 dicot amaranth were linked to a gusA reporter gene. These were constitutively transcribed from a cauliflower mosaic virus promoter and assayed for posttranscriptional expression patterns in transgenic lines of the C4 dicot Flaveria bidentis. Three characteristic C4 expression patterns were conferred by heterologous AhRbcS1 UTRs in transgenic F. bidentis. First, the AhRbcS1 UTRs conferred strong translational enhancement of gusA expression, relative to control constructs lacking these UTRs. Second, while the UTRs did not appear to confer tissue-specific expression when analyzed by β-glucuronidase activity assays, differences in gusA mRNA accumulation were observed in leaves, stems, and roots. Third, the AhRbcS1 UTRs conferred preferential gusA expression (enzyme activity and gusA mRNA accumulation) in leaf bundle sheath cells. AhRbcS1 UTR-mediated translational enhancement was also observed in transgenic C3 plants (tobacco [Nicotiana tabacum]) and in in vitro translation extracts. These mRNAs appear to be translated with different efficiencies in C4 versus C3 plants, indicating that processes determining overall translational efficiency may vary between these two categories of higher plants. Our findings suggest that the AhRbcS1 5′-UTR functions as a strong translational enhancer in leaves and other tissues, and may work synergistically with the 3′-UTR to modulate overall levels of Rubisco gene expression in different tissues and cell types of C4 plants.

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Section: Discussionmentioning

confidence: 99%

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

et al. 2004

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“…C 4 plants generally have high PEPC activity in the cytosol of mesophyll cells, allowing for the accumulation of four-carbon acids that subsequently diffuse into the bundle sheath cells (BSCs) for decarboxylation (Kanai and Edwards, 1999;Furbank et al, 2000). The specialized biochemistry and leaf anatomy of C 4 plants results in CO 2 partial pressure (pCO 2 ) around the site of Rubisco severalfold higher than current atmospheric levels, significantly reducing the rates of photorespiration (Hatch, 1987).…”

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confidence: 99%

The Role of Phosphoenolpyruvate Carboxylase during C4 Photosynthetic Isotope Exchange and Stomatal Conductance

Cousins

Baroli²,

Badger³

et al. 2007

Plant Physiology

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Phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) plays a key role during C 4 photosynthesis and is involved in anaplerotic metabolism, pH regulation, and stomatal opening. Heterozygous (Pp) and homozygous (pp) forms of a PEPC-deficient mutant of the C 4 dicot Amaranthus edulis were used to study the effect of reduced PEPC activity on CO 2 assimilation rates, stomatal conductance, and 13 CO 2 (D 13 C) and C 18 OO (D 18 O) isotope discrimination during leaf gas exchange. PEPC activity was reduced to 42% and 3% and the rates of CO 2 assimilation in air dropped to 78% and 10% of the wild-type values in the Pp and pp mutants, respectively. Stomatal conductance in air (531 mbar CO 2 ) was similar in the wild-type and Pp mutant but the pp mutant had only 41% of the wild-type steady-state conductance under white light and the stomata opened more slowly in response to increased light or reduced CO 2 partial pressure, suggesting that the C 4 PEPC isoform plays an essential role in stomatal opening. There was little difference in D 13C between the Pp mutant (3.0& 6 0.4&) and wild type (3.3& 6 0.4&), indicating that leakiness (f), the ratio of CO 2 leak rate out of the bundle sheath to the rate of CO 2 supply by the C 4 cycle, a measure of the coordination of C 4 photosynthesis, was not affected by a 60% reduction in PEPC activity. In the pp mutant D 13 C was 16& 6 3.2&, indicative of direct CO 2 fixation by Rubisco in the bundle sheath at ambient CO 2 partial pressure. D 18O measurements indicated that the extent of isotopic equilibrium between leaf water and the CO 2 at the site of oxygen exchange (u) was low (0.6) in the wild-type and Pp mutant but increased to 0.9 in the pp mutant. We conclude that in vitro carbonic anhydrase activity overestimated u as compared to values determined from D 18O in wild-type plants.

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“…Because the C 4 cycle consumes energy in the form of ATP during the regeneration of PEP, leakage of CO 2 out of the bundle sheath is an energy cost to the leaf and coordination between the C 3 and C 4 cycle is important. Biochemical interdependence of the two cycles exists at several levels (Hatch and Osmond, 1976;Furbank et al, 2000). Among these, regulation of PEPC activity by phosphorylation has been hypothesized to provide a possible link between PEPC activity and coordination of C 4 and C 3 cycle activity (Bakrim et al, 1993;Vidal and Chollet, 1997).…”

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Phosphorylation of Phosphoenolpyruvate Carboxylase Is Not Essential for High Photosynthetic Rates in the C₄ Species Flaveria bidentis

et al. 2007

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Phosphoenolpyruvate carboxylase (PEPC; EC4.1.1.31) plays a key role during C 4 photosynthesis. The enzyme is activated by metabolites such as glucose-6-phosphate and inhibited by malate. This metabolite sensitivity is modulated by the reversible phosphorylation of a conserved serine residue near the N terminus in response to light. The phosphorylation of PEPC is modulated by a protein kinase specific to PEPC (PEPC-PK). To explore the role PEPC-PK plays in the regulation of C 4 photosynthetic CO 2 fixation, we have transformed Flaveria bidentis (a C 4 dicot) with antisense or RNA interference constructs targeted at the mRNA of this PEPC-PK. We generated several independent transgenic lines where PEPC is not phosphorylated in the light, demonstrating that this PEPC-PK is essential for the phosphorylation of PEPC in vivo. Malate sensitivity of PEPC extracted from these transgenic lines in the light was similar to the malate sensitivity of PEPC extracted from darkened wild-type leaves but greater than the malate sensitivity observed in PEPC extracted from wild-type leaves in the light, confirming the link between PEPC phosphorylation and the degree of malate inhibition. There were, however, no differences in the CO 2 and light response of CO 2 assimilation rates between wild-type plants and transgenic plants with low PEPC phosphorylation, showing that phosphorylation of PEPC in the light is not essential for efficient C 4 photosynthesis for plants grown under standard glasshouse conditions. This raises the intriguing question of what role this complexly regulated reversible phosphorylation of PEPC plays in C 4 photosynthesis.

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C4 Photosynthesis: Mechanism and Regulation

Cited by 40 publications

References 106 publications

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

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

The Role of Phosphoenolpyruvate Carboxylase during C4 Photosynthetic Isotope Exchange and Stomatal Conductance

Phosphorylation of Phosphoenolpyruvate Carboxylase Is Not Essential for High Photosynthetic Rates in the C₄ Species Flaveria bidentis

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C4 Photosynthesis: Mechanism and Regulation

Cited by 40 publications

References 106 publications

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

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

The Role of Phosphoenolpyruvate Carboxylase during C4 Photosynthetic Isotope Exchange and Stomatal Conductance

Phosphorylation of Phosphoenolpyruvate Carboxylase Is Not Essential for High Photosynthetic Rates in the C4 Species Flaveria bidentis

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Phosphorylation of Phosphoenolpyruvate Carboxylase Is Not Essential for High Photosynthetic Rates in the C₄ Species Flaveria bidentis