New insights on sucrose metabolism: evidence for an active A/N-Inv in chloroplasts uncovers a novel component of the intracellular carbon trafficking

Abstract

The presence of sucrose (Suc) in plastids was questioned for several decades. Although it was reported some decades ago, neither Suc transporters nor Suc metabolizing enzymes were demonstrated to be active in those organelles. By biochemical, immunological, molecular and genetic approaches we show that alkaline/neutral invertases (A/N-Invs) are also localized in chloroplasts of spinach and Arabidopsis. A/N-Inv activity and polypeptide content were shown in protein extracts from intact chloroplasts. Moreover, we functionally characterized the Arabidopsis At-A/N-InvE gene coding for a chloroplast-targeted A/N-Inv. The At-A/N-InvE knockout plants displayed a lower total A/N-Inv activity in comparison with wild-type plants. Furthermore, neither A/N-Inv activity nor A/N-Inv polypeptides were detected in protein extracts prepared from chloroplasts of mutant plants. Also, the measurement of carbohydrate content, in leaves harvested either at the end of the day or at the end of the night period, revealed that the knockout plants showed a decrease in starch accumulation but no alteration in Suc levels. These are the first results demonstrating the presence of a functional A/N-Inv inside chloroplasts and its relation with carbon storage in Arabidopsis leaves. Taken together our data and recent reports, we conclude that the participation of A/N-Invs in the carbon flux between the cytosol and the plastids may be a general phenomenon in plants.

Metabolic Profiling during Peach Fruit Development and Ripening Reveals the Metabolic Networks That Underpin Each Developmental Stage

“…Nevertheless, the particular response of each NI during peach development and different postharvest treatments (Lara et al, , 2011 indicates that NI transcripts display particular roles that will require further analyses. This hypothesis is reinforced by the discovery of novel physiological functions (Roitsch and González, 2004) and compartmentalization of invertases (Vargas et al, 2008;Vargas and Salerno, 2010). On the other hand, an increase in SS and SPS2 levels was also detected during postharvest peach ripening (Fig.…”

An Integrated Genomics Approach to Define Niche Establishment byRhodococcus fascians

“…The cell wall (FRUCT1 and FRUCT2) and vacuolar (FRUCT3 and FRUCT4) invertases were amplified in 25 cycles with primers described by Tymowska-Lalanne and Kreis (1998). The expression profile of the cytoplasmic/neutral invertases was examined with primers developed by Vargas et al (2008) in 22 amplification cycles. The RbcS primer set was obtained from Laval et al (2002), and CAB2 was amplified with primers described by Delessert et al (2004), both in 18 amplification cycles.…”

Understanding the Role of Defective Invertases in Plants: Tobacco Nin88 Fails to Degrade Sucrose

“…These enzymes have long remained poorly studied, and for decades, A/N-Invs were believed to occur exclusively in the cytosol. However, recent studies clearly demonstrated the presence of A/N-Invs in various organelles in addition to the cytosol (Vargas et al, 2008;Xiang et al, 2011). It is now clear that A/N-Invs play an important role in plant development and stress tolerance (Barratt et al, 2009;Vargas and Salerno, 2010;Xiang et al, 2011).…”