Changes in SBPase activity influence photosynthetic capacity, growth, and tolerance to chilling stress in transgenic tomato plants.

Fei Ding,Shuoxin Zhang,Xizhen Ai,Meiling Wang

doi:10.1038/srep32741

Abstract

Sedoheptulose-1, 7-bisphosphatase (SBPase) is an important enzyme involved in photosynthetic carbon fixation in the Calvin cycle. Here, we report the impact of changes in SBPase activity on photosynthesis, growth and development, and chilling tolerance in SBPase antisense and sense transgenic tomato (Solanum lycopersicum) plants. In transgenic plants with increased SBPase activity, photosynthetic rates were increased and in parallel an increase in sucrose and starch accumulation was evident. Total biomass and leaf area were increased in SBPase sense plants, while they were reduced in SBPase antisense plants compared with equivalent wild-type tomato plants. Under chilling stress, when compared with plants with decreased SBPase activity, tomato plants with increased SBPase activity were found to be more chilling tolerant as indicated by reduced electrolyte leakage, increased photosynthetic capacity, and elevated RuBP regeneration rate and quantum efficiency of photosystem II. Collectively, our data suggest that higher level of SBPase activity gives an advantage to photosynthesis, growth and chilling tolerance in tomato plants. This work also provides a case study that an individual enzyme in the Calvin cycle may serve as a useful target for genetic engineering to improve production and stress tolerance in crops.

Highlights

The Calvin cycle is the primary pathway for photosynthetic carbon fixation in C3 plants and takes place in the stroma of chloroplasts
Sequence alignment analysis revealed that SlSBPase shared 81%, 84%, 79% and 78% homology to SBPase amino acid sequences of Arabidopsis thaliana, Cucumis sativus, Oryza sativa and Triticum aestivum, respectively (Fig. 1c), indicating that the evolution of SBPase is highly conservative
In parallel with the decreases in photosynthetic rate, chilling stress induced great reductions in RuBP regeneration rate in all plants, a relatively higher RuBP regeneration rate was maintained in SBPase sense plants with higher levels of SBPase activity (Fig. 7d). These results indicate that changes in SBPase activity may affect photosynthetic capacity by altering the capacity for RuBP regeneration in tomato plants, consistent with a previous report that decreases in SBPase activity in transgenic tobacco plants limit carbon assimilation by reducing the capacity for RuBP regeneration[33]

Summary

Introduction

The Calvin cycle is the primary pathway for photosynthetic carbon fixation in C3 plants and takes place in the stroma of chloroplasts. The enzyme sedoheptulose-1, 7-bisphosphatase (SBPase: EC 3.1.3.37) functions at the branch point where assimilated carbon may either go to the regenerative phase to produce the CO2 acceptor molecule RuBP in the cycle or be exported from the cycle for sucrose or transitory starch biosynthesis. Overexpression of SBPase protects transgenic rice against salt stress and high temperature stress by providing more regeneration of the CO2 acceptor molecule RuBP in the stroma[21,22] All these lines of evidence suggest that SBPase plays a critical role in control over carbon flow in the Calvin cycle. This work provides a case study that an individual enzyme in the Calvin cycle is a useful target for genetic engineering to improve production and stress tolerance in horticultural plants

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Conclusion