Temporally extended gene expression of the ADP-Glc pyrophosphorylase large subunit (AgpL1) leads to increased enzyme activity in developing tomato fruit

Abstract

Tomato plants (Solanum lycopersicum) harboring the allele for the AGPase large subunit (AgpL1) derived from the wild species Solanum habrochaites (AgpL1 ( H )) are characterized by higher AGPase activity and increased starch content in the immature fruit, as well as higher soluble solids in the mature fruit following the breakdown of the transient starch, as compared to fruits from plants harboring the cultivated tomato allele (AgpL1 ( E )). Comparisons of AGPase subunit gene expression and protein levels during fruit development indicate that the increase in AGPase activity correlates with a prolonged expression of the AgpL1 gene in the AgpL1 ( H ) high starch line, leading to an extended presence of the L1 protein. The S1 (small subunit) protein also remained for an extended period of fruit development in the AgpL1 ( H ) fruit, linked to the presence of the L1 protein. There were no discernible differences between the kinetic characteristics of the partially purified AGPase-L1(E) and AGPase-L1(H) enzymes. The results indicate that the increased activity of AGPase in the AgpL1 ( H ) tomatoes is due to the extended expression of the regulatory L1 and to the subsequent stability of the heterotetramer in the presence of the L1 protein, implying a role for the large subunit not only in the allosteric control of AGPase activity but also in the stability of the AGPase L1-S1 heterotetramer. The introgression line of S. lycopersicum containing the wild species AgpL1 ( H ) allele is a novel example of transgressive heterosis in which the hybrid multimeric enzyme shows higher activity due to a modulated temporal expression of one of the subunits.

Gene and Metabolite Regulatory Network Analysis of Early Developing Fruit Tissues Highlights New Candidate Genes for the Control of Tomato Fruit Composition and Development

“…Both the nutritional and the sensorial attributes are built throughout the successive phases of fruit development, namely cell division, cell expansion, and ripening. While the fruitripening process is obviously important (Giovannoni, 2001), there is also a growing body of evidence that supports the key role of early fruit development for the acquisition of several fruit quality traits, including the accumulation of sugars and organic acids (Guillet et al, 2002;Lemaire-Chamley et al, 2005;Petreikov et al, 2006), the determination of cell wall and texture characteristics (Chaïb et al, 2007), and the cuticle biosynthesis (Mintz-Oron et al, 2008). In the growing fruit, these processes mainly take place during the cell expansion phase, which sustains fruit growth by allowing a large increase in fruit cell volume linked with membrane and cell wall/synthesis and the con-comitant accumulation of water, mineral ions, and metabolites in the vacuoles, thereby conferring its fleshy characteristics to the fruit.…”

Overexpression of the phosphoenolpyruvate carboxykinase gene (<i>SlPEPCK</i>) promotes soluble sugar accumulation in fruit and post-germination growth of tomato (<i>Solanum lycopersicum</i> L.)

“…Prior to the constructions, a whole cDNA sequence of SlPEPCK (accession no. AY007226, Bahrami et al 2001) was cloned by RT-PCR using total RNA extracted from tomato fruit with gene-specific primers as follows: FW 5′-CAC CAT GGC GTC GAA CGG AGT C-3′ and RW 5′-TTA GAA GTT TGG ACC AGC TGC C-3′, and transferred Petreikov et al 2006) was used as an internal standard with the following primers: FW 5′-CAC CAT TGG GTC TGA GCG AT-3′ and Rev 5′-GGG CGA CAA CCT TGA TCT TC-3′. The SlPEPCK cDNA sequence (Bahrami et al 2001) was amplified using the following sequence of the primer set FW 5′-GAA TAC AAG AAG ACC GAG GTA-3′ and Rev 5′-CTC AAA ATT CTT CCT AAA TAG G-3′.…”

Isolation and characterisation of the ADP-glucose pyrophosphorylase small subunit gene (AgpS1) promoter in tomato (Solanum lycopersicum L.)

“…It has been reported that starch accumulation during early development in tomato fruit affects the sugar level of redripe fruit (Baxter et al 2005;Petreikov et al 2006;Yin et al 2010). ADP-glucose pyrophosphorylase (AGPase,EC2.7.7.27) catalyses the first regulatory step in starch biosynthesis in plants (Lin et al 1988;Müller-Röber et al 1992;Stark et al 1992;Tsai and Nelson 1966): the synthesis of ADP-glucose from glucose-1-phosphate and ATP (Preiss 1988).…”

“…In tomato, one gene encoding the small subunit and three genes encoding the large subunit have been identified thus far (Chen et al 1998;Park and Chung, 1998), with AgpS1 and AgpL1, encoding a small and large subunit, are predominantly expressed and are responsible for starch accumulation in early developing fruit (Park and Chung 1998;Petreikov et al 2006;Yin et al 2010). It has been reported that plant AGPase genes are regulated at the transcriptional level by phosphate, nitrate and sugars (Li et al 2002;Müller-Röber et al 1990;Nielsen et al 1998;Scheible et al 1997;Sokolov et al 1998).…”