Abstract
Sedoheptulose-1,7-bisphosphatase (SBPase) is an enzyme in the Calvin–Benson cycle and has been documented to be important in carbon assimilation, growth and stress tolerance in plants. However, information on the impact of SBPase on carbon assimilation and nitrogen metabolism in tomato plants (Solanum lycopersicum) is rather limited. In the present study, we investigated the role of SBPase in carbon assimilation and nitrogen metabolism in tomato plants by knocking out SBPase gene SlSBPASE using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) gene editing technology. Compared with wild-type plants, slsbpase mutant plants displayed severe growth retardation. Further analyses showed that knockout of SlSBPASE led to a substantial reduction in SBPase activity and as a consequence, ribulose-1,5-bisphosphate (RuBP) regeneration and carbon assimilation rate were dramatically inhibited in slsbpase mutant plants. It was further observed that much lower levels of sucrose and starch were accumulated in slsbpase mutant plants than their wild-type counterparts during the photoperiod. Intriguingly, mutation in SlSBPASE altered nitrogen metabolism as demonstrated by changes in levels of protein and amino acids and activities of nitrogen metabolic enzymes. Collectively, our data suggest that SlSBPASE is required for optimal growth, carbon assimilation and nitrogen metabolism in tomato plants.
Highlights
The Calvin–Benson cycle is the primary pathway of photosynthetic carbon fixation in higher plants
We have previously investigated the importance of tomato SBPase gene SlSBPASE (Solyc05g052600) in the photosynthetic carbon assimilation and growth in tomato plants [23]
Our previous studies on SBPase using either SBPase overexpressing or antisense transgenic tomato plants have exhibited a critical role of SBPase in photosynthetic carbon assimilation [23,24]
Summary
The Calvin–Benson cycle is the primary pathway of photosynthetic carbon fixation in higher plants. The cycle is central to plant metabolism, providing intermediates for biosynthesis of sucrose, starch, isoprenoid and shikimic acid [1]. There are a total of 11 different enzymes that catalyze 13 reactions, which are divided into three distinct phases, including carboxylation of ribulose-1,5-bisphosphate (RuBP), reduction of 3-phosphoglycerate and regeneration of the CO2 acceptor RuBP [2]. The enzyme sedoheptulose-1,7-bisphosphatase (SBPase) catalyzes the dephosphorylation of sedoheptulose-1,7-bisphosphate to sedoheptulose-7-phosphate, acting in the regeneration of CO2 acceptor molecule RuBP in the Calvin–Benson cycle. Like other enzymes in the Calvin-Benson cycle, SBPase is activated via ferredoxin/thioredoxin system in response to light [5,6]
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