ADP-Glucose Pyrophosphorylase Is Located in the Plastid in Developing Tomato Fruit

Abstract

The subcellular location of activity and protein of ADP-glucose pyrophosphorylase (AGPase) in developing tomato (Lycopersicon esculentum) fruit was determined following a report that the enzyme might be present inside and outside the plastids in this organ. Plastids prepared from crude homogenates of columella and pericarp, the starch-accumulating tissues of developing fruit, contained 8% to 18% of the total activity of enzymes known to be confined to plastids, and 0.2% to 0.5% of the total activity of enzymes known to be confined to the cytosol. The proportion of the total activity of AGPase in the plastids was the same as that of the enzymes known to be confined to the plastid. When samples of plastid and total homogenate fractions were subjected to immunoblotting with an antiserum raised to AGPase, most or all of the protein detected was plastidial. Taken as a whole, these data provide strong evidence that AGPase is confined to the plastids in developing tomato fruit.

SlARF4, an Auxin Response Factor Involved in the Control of Sugar Metabolism during Tomato Fruit Development

“…The regulation of starch synthesis has received much attention in tomato fruit (Beckles et al, 2001a(Beckles et al, , 2001b, and it has been reported that the reaction catalyzed by AGPase is the limiting step for starch biosynthesis in potato (Solanum tuberosum) tubers (Tiessen et al, 2002), a Solanaceae species close to tomato. Indeed, modifying AGPase activity and properties has a direct impact on starch levels in plants (Tsai and Nelson, 1966;Smidansky et al, 2002;Berger et al, 2004;Hädrich et al, 2012).…”

Isolation and characterization of cDNAs and genomic DNAs encoding ADP-glucose pyrophosphorylase large and small subunits from sweet potato

“…All dicotyledonous plant AGPases studied thus far are plastidic proteins, whereas cereal endosperm AGPase is both cytoplasmic and plastidic (Beckles et al 2001;James et al 2003). The subcellular location and transit peptide sequences of the six sweet potato AGPase isoforms were mainly predicted using TargetP (http:// www.cbs.dtu.dk/services/TargetP/).…”

Recent progress toward understanding the role of starch biosynthetic enzymes in the cereal endosperm

“…The enzyme is now known to be largely extra-plastidial (i.e. 85-95%) in cereal endosperm, but plastidial in other cereal tissues and in all tissues of non-cereal plants [16,[26][27][28][29][30]. The starch-deficient kernel phenotypes of maize shrunken2 and brittle2 is caused by the loss of endosperm-specific cytosolic AGP-L and AGP-S isoforms, respectively, suggesting that plastidial AGPase by itself is not sufficient to support the normal processes of starch biosynthesis in cereal endosperm [31][32][33][34].…”

“…It starts with individual chains as the first level, which are formed by ADP-glucose through (1→4)-α-glycosidic linkages. Those chains in amylopectin have been further denoted as C chains having the reducing end, A chains (degree of polymerization, DP, [6][7][8][9][10][11][12] carrying no branches, B1 chains (DP [13][14][15][16][17][18][19][20][21][22][23][24] carrying A chains, B2 chains (DP DOI 10.1515/amylase-2017-0006 [25][26][27][28][29][30][31][32][33][34][35][36] carrying B1 chains, B3 chains (DP > 36) carrying B2 chains, and so on (for a recent review, see [2]). Although still occasionally one finds statements to the contrary, amylose is not solely linear, but contains a small but significant number of long-chain branches [3].…”