An ATP synthase harboring an atypical γ–subunit is involved in ATP synthesis in tomato fruit chromoplasts

Abstract

SUMMARYChromoplasts are non-photosynthetic plastids specialized in the synthesis and accumulation of carotenoids. During fruit ripening, chloroplasts differentiate into photosynthetically inactive chromoplasts in a process characterized by the degradation of the thylakoid membranes, and by the active synthesis and accumulation of carotenoids. This transition renders chromoplasts unable to photochemically synthesize ATP, and therefore these organelles need to obtain the ATP required for anabolic processes through alternative sources. It is widely accepted that the ATP used for biosynthetic processes in non-photosynthetic plastids is imported from the cytosol or is obtained through glycolysis. In this work, however, we show that isolated tomato (Solanum lycopersicum) fruit chromoplasts are able to synthesize ATP de novo through a respiratory pathway using NADPH as an electron donor. We also report the involvement of a plastidial ATP synthase harboring an atypical c-subunit induced during ripening, which lacks the regulatory dithiol domain present in plant and algae chloroplast c-subunits. Silencing of this atypical c-subunit during fruit ripening impairs the capacity of isolated chromoplast to synthesize ATP de novo. We propose that the replacement of the c-subunit present in tomato leaf and green fruit chloroplasts by the atypical c-subunit lacking the dithiol domain during fruit ripening reflects evolutionary changes, which allow the operation of chromoplast ATP synthase under the particular physiological conditions found in this organelle.

Tomato Fruit Chromoplasts Behave as Respiratory Bioenergetic Organelles during Ripening

“…Nievelstein et al (1995) observed a similar respiratory response to NADH, NADPH, and the uncoupler 2,4-dinitrophenol in chromoplasts isolated from daffodil flowers. Pateraki et al, (2013) recently reported the stimulatory effect of NADPH and CCCP on oxygen uptake rates in tomato chromoplasts. Our results are also consistent with the reported existence of an active H + -ATP synthase in tomato (Pateraki et al, 2013) and daffodil (Morstadt et al, 2002) chromoplasts.…”

“…Pateraki et al, (2013) recently reported the stimulatory effect of NADPH and CCCP on oxygen uptake rates in tomato chromoplasts. Our results are also consistent with the reported existence of an active H + -ATP synthase in tomato (Pateraki et al, 2013) and daffodil (Morstadt et al, 2002) chromoplasts.…”

“…In daffodil chromoplast homogenates (Nievelstein et al, 1995) as well as in isolated tomato fruit chromoplasts (Pateraki et al, 2013), NAD(P)H acts as an electron donor for chromorespiration, indicating the participation of NAD (P)H plastoquinone oxidoreductase activity. Considering that tomato fruit chromoplasts derive from chloroplasts, it is possible that some components of the chromoplastic redox pathway could originate from chlororespiration, such as the NAD(P)H:plastoquinone-reductase complex (NDH), which could act as the electron entrance.…”

“…Morstadt et al (2002) found that liposomes containing daffodil chromoplast proteins and energized by an acid-base transition were able to produce ATP through a chemiosmotic mechanism, demonstrating that daffodil chromoplasts contain a functional H + -ATP synthase complex. We recently reported that isolated chromoplasts from tomato fruits can synthesize ATP de novo (Pateraki et al, 2013). This process is dependent on an ATP synthase complex containing an atypical g-subunit without the regulatory dithiol domain, which may be active using lower proton gradients than those present in the chloroplast (Pateraki et al, 2013).…”

“…We recently reported that isolated chromoplasts from tomato fruits can synthesize ATP de novo (Pateraki et al, 2013). This process is dependent on an ATP synthase complex containing an atypical g-subunit without the regulatory dithiol domain, which may be active using lower proton gradients than those present in the chloroplast (Pateraki et al, 2013). This finding is consistent with proteomic analyses that reveal that several proteins related to electron transport and ATP production are present in chromoplasts of ripe fruits, like ATP synthase, some subunits of the NDH complex, and the cytochrome b 6 f complex (Barsan et al, 2012;Wang et al, 2013).…”