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PII signal transducing protein

AtPII is a small plastidial protein highly conserved in plants, algae and prokaryotes (Figure 1). AtPII is a sensor protein of the energetic and C status of the cell due to ATP and 2-oxoglutarate binding. These effectors control the allosteric interaction of AtPII with other protein partners on a conserved domain (T-Loop).

Figure 1: PII phylogeny tree (from Uhrig et al. 2009)

 


Main Results

Two AtPII protein partners have been identified in plants: NAGK a key enzyme of Arginine synthesis and BCCP2 a subunit of HtACCase a key enzyme of fatty acid synthesis.

AtPII activates NAGK activity and then a reduced ornithine, citrulline and arginine accumulation was observed in response to NH4+ resupply after N starvation in shoots of AtPII mutants (Figure 2) [1].

figure 2
Figure 2: Ornithine (A), citrulline (B) and arginine (C) contents in PII
mutants grown under varying nitrogen conditions. WS wild type (light
grey bar), Col wild-type (white bar), PIIV1 mutants (dark bar) and
PIIS2 mutants (grey bar) plants were grown hydroponically under
controlled conditions and 1 mM NO3- for 5 weeks (t5, 1 mM NO3-),
submitted to 5 days of N deficiency (t5, 0 mM NO3-) and then
resupplied for 4 days with 1 mM NH4+ (t9, 1 mM NH4) or 5 mM NH4+
(t9, 5 mM NH4+). The values are measurements performed on the
extracts of three pooled plants.

 

In seeds AtPII is localized in plastids of maturing embryo (Figure 3) and inhibits HtACCase activity leading to a decreased amounts of modified (elongated, desaturated) fatty acid species (Figure 4) [2].

figure 3

Figure 3 : Spatial pattern of PII accumulation in maturing embryos (Col-0 accession).
(a) Immunolocalization using specific anti-PII antibodies and secondary antibodies conjugated to Alexa Fluor 488. The fluorescence of the labelled secondary antibody (495–585 nm) is visualized by confocal laser microscopy on a longitudinal section from a silique aged 15 days after anthesis and appears as a green signal.
(b) Negative control sample incubated only with secondary antibodies conjugated to Alexa Fluor 488.
(c–e) Co-immunolocalization using anti-E37 primary antibodies raised against a marker protein of the inner plastidial membrane and secondary antibodies conjugated to Alexa Fluor 568 (fluorescence observed at 603–682 nm; red signal) (c) or specific anti-PII antibodies and secondary antibodies conjugated to Alexa Fluor 488 (fluorescence observed at 495–585 nm; green signal) (d). A merged picture is shown in (e).

 

 

 

Figure 4: Pattern of fatty acid accumulation in developing seeds of wild-type(WT) and pII lines grown on 10 mM NO3-).
(a) Total fatty acid content.
(b) Very long chain fatty acid (VLCFA)/long chain fatty acid (LCFA) ratio. Total lipid extraction was carried out on batches of 20 seeds. Total fatty acid content and fatty acid composition were determined by GC analysis of an aliquot. Values are the means _ SE of four replicates carried out on seeds from distinct individuals. VLCFA/LCFA ratio = (P C20:0, C20:1, C20:2, C22:0, C22:1 in mol%)/(P C16:0, C18:0, C18:1, C18:2, C18:3 in mol%). ***Significant difference according to a Student’s t-test (P < 0.001).

 

 

AtPII has also been suggested to be involved in the control of nitrite uptake into chloroplasts (Figure 5) [3 ].

Figure 5 : Kinetics of 15NO2Na uptake in the light (full bars) and in the dark (lined bars) into chloroplasts isolated from WS (dark bar) and from the pIIv1 mutant (gray bar) as a function of the time of incubation. The values are the means of four independent replicated.

 


Publications

Ferrario-Méry, S., Besin, E., Pichon, O., Meyer, C. and Hodges, M. (2006) The regulatory PII protein controls arginine biosynthesis in Arabidopsis. FEBS Lett. 580, 2015–2020.

Baud S, Bourrellier ABF, Azzopardi M, Berger A., Dechorgnat J, Daniel-Vedele F, Lepiniec L, Miquel M, Rochat C, Hodges M, Ferrario-Mery S (2010). PII is induced by WRINKLED1 and fine-tunes fatty acid composition in seeds of Arabidopsis thaliana. Plant Journal 64: 291-303.

Ferrario-Méry S, Meyer C, Hodges M (2008) Chloroplast nitrite uptake is enhanced in Arabidopsis pII mutants. FEBS Lett 582, 1061-1066

 

 

 

 

 
 

 

 

 

 
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