Engineering of the cytosolic form of phosphoglucose isomerase into chloroplasts improves plant photosynthesis and biomass

Abstract

Starch is the most abundant carbohydrate synthesized in plant chloroplast as the product of photosynthetic carbon assimilation, serving a crucial role in the carbon budget as storage energy. Phosphoglucose isomerase (PGI) catalyzes the interconversion between glucose 6phosphate (G6P) and fructose 6-phosphate (F6P), which are important metabolic molecules in starch synthesis within chloroplasts and sucrose synthesis in cytosol.Here, we found that the specific activity of recombinantly purified PGI localized in cytosolic PGI (PGIc) was much higher than its plastidic isoenzyme counterpart (PGIp) originated from wheat, rice and Arabidopsis, with wheat PGIc having by far the highest activity. Crystal structures of wheat TaPGIc and TaPGIp proteins were solved and the functional units were homodimers.The active sites of PGIc and PGIp, constituted by the same amino acids, formed different binding pockets. Moreover, PGIc showed slightly lower affinity to the substrate F6P but with much faster turnover rates. Engineering of TaPGIc into chloroplasts of a pgip mutant of Arabidopsis thaliana (atpgip) resulted in starch overaccumulation, increased CO 2 assimilation, up to 19% more plant biomass and 27% seed yield productivity.These results show that manipulating starch metabolic pathways in chloroplasts can improve plant biomass and yield productivity.

A structural basis for the functional differences between the cytosolic and plastid phosphoglucose isomerase isozymes

“…In our previous work, the dimeric structures of TaPGIp and TaPGIc were first reported in plants. We described some general different structural features between this pair of isozymes [ 1 ], but the detailed structural divergence between these two proteins has not been described. Here, we present a detailed structural analysis of these two isomerase twins.…”

“…During glycolysis, phosphoglucose isomerase (PGI, EC 5.3.1.9) catalyzes the reversible isomerization of glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P). Two kinds of separately evolving PGI isoenzymes, plastidic (PGIp) and cytosolic (PGIc) PGIs, have been previously detected in different sublocations in higher plants [ 1 ]. The biochemical properties of these PGIs, such as catalyzing activity, thermal stability, and substrate turnover rate in vitro, are dramatically different [ 1 ].…”

“…Two kinds of separately evolving PGI isoenzymes, plastidic (PGIp) and cytosolic (PGIc) PGIs, have been previously detected in different sublocations in higher plants [ 1 ]. The biochemical properties of these PGIs, such as catalyzing activity, thermal stability, and substrate turnover rate in vitro, are dramatically different [ 1 ]. However, in vivo studies reveal that PGIc and PGIp are both involved in diverse mechanisms of glucose synthesis (sucrose, starch) [ 2 , 3 ].…”

“…In our previous work [ 1 ], three PGI crystal structures (TaPGIc, TaPGIc-G6P and TaPGIp) were solved for the first time in higher plants. We established that the TaPGI isozymes have different properties, including catalytic activity and substrate binding affinity, which can probably be ascribed to their location in different organelles.…”

Proteomics data analysis using multiple statistical approaches identified proteins and metabolic networks associated with sucrose accumulation in sugarcane

“…Glucose-6-phosphote isomerase catalyzes the inter-conversion of glucose 6-phosphate and fructose 6-phosphate, which plays an important role in sucrose synthesis. Over-expression of a wheat glucose-phosphate isomerase gene TaPGIc in Arabidopsis thaliana improved plant photosythesis, starch over-accumulation, biomass and yield [ 42 ].…”