Isolation and analysis of cDNA clones encoding the large subunits of ADP-glucose pyrophosphorylase from tomato

Abstract

Three cDNAs encoding different isoforms of ADP-glucose pyrophosphorylase large subunits were isolated and characterized from tomato plants. Three clones, designated AgpL1, AgpL2, and AgpL3 were 2019, 2105, and 1850 bp, respectively. Each of the clones had a long, uninterrupted open reading frame (ORF) with a start codon at the 5`` region and different copies of polyadenylation signal at the 3`` region, deriving 57-58 kDa polypeptide. The ORFs of AgpL1, AgpL2, and AgpL3 consist of 1554, 1572, and 1548 nucleotides, respectively. Genomic DNA blot analysis suggests that AgpL1 and AgpL2 may be single-copy genes, and AgpL3 be a double-copy gene. The identities between the deduced amino acid sequences of the isoforms were 67 % (AGPL1-AGPL2), 61% (AGPL1-AGPL3), and 61% (AGPL2-AGPL3). Tomato AGPL1, AGPL2, and AGPL3 showed the highest identities with potato AGPS (98%), AGPS2 (96%), and AGPS3 (96%), respectively. Phylogenetic analysis revealed that the three isoforms were diverged into different branches on molecular evolution of plant AGP large subunits. The highest expression of AgpL1 occurred in stems and weak expression in roots. Accumulation of AgpL1 transcripts was found even in unpollinated ovaries and sustained at the early stage of fruit development. AgpL2 was expressed in roots and in fruits of all developmental stages investigated, but the expression levels were relatively lower. AgpL3 was exclusively expressed in leaves, whereas AgpL1 and AgpL2 transcripts were not detected in leaves. The present study suggests that the three isoforms of tomato AGP large subunits are organ-specific in their expressions.