Photoprotective effects of high level expression of C₄ phosphoenolpyruvate carboxylase in transgenic rice during photoinhibition

Abstract

With untransformed rice cv. Kitaake as control, the characteristics of carbon assimilation and photoprotection of a transgenic rice line over-expressing maize phosphoenolpyruvate carboxylase (PEPC) were investigated. The PEPC activity in untransformed rice was low, but the activity was stimulated under high irradiance or photoinhibitory condition. PEPC in untransformed rice contributed by about 5-10 % to photosynthesis, as shown by the application of the specific inhibitor 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)propenoate (DCDP). When maize PEPC gene was introduced into rice, transgenic rice expressed high amount of maize PEPC protein and had high PEPC activity. Simultaneously, the activity of carbonic anhydrase (CA) transporting CO 2 increased significantly. Thus the photosynthetic capacity increased greatly (50 %) under high CO 2 supply. In CO 2 -free air, CO 2 release in the leaf was less. In addition, PEPC transgenic rice was more tolerant to photoinhibition. Treating by NaF, an inhibitor of phosphatase, showed that in transgenic rice more phosphorylated light-harvesting chlorophyll a/b-binding complexes (LHC) moved to photosystem 1 (PS1) protecting thus PS2 from photo-damage. Simultaneously, the introduction of maize PEPC gene could activate or induce activities of the key enzymes scavenging active oxygen, such as superoxide dismutase (SOD) and peroxidase (POD). Hence higher PS2 photochemical efficiency and lower superoxygen anion (O 2˙-) generation and malonyldiadehyde (MDA) content under photoinhibition could improve protection from photo-oxidation.

Photosynthetic characteristics of hybrid rice with phosphoenolpyruvate carboxylase gene

“…Moreover, the photosynthetic characteristics and the tolerance to photoinhibition and photo-oxidation in JAAS45 were similar to those of the male parent. On the other hand, we also found that JAAS45, similar to PEPC transgenic rice, possesses a limiting C 4 -like cycle with primitive CO 2 concentrating mechanism (Jiao et al 2003). All this suggests that the PEPC transgenic rice can transfer over-expression of PHOTOSYNTHETIC CHARACTERISTICS OF HYBRID RICE WITH PHOSPHOENOLPYRUVATE CARBOXYLASE GENE PEPC activity and the C 4 photosynthetic characteristics into conventional rice.…”

“…Till now, only a few systematic studies on photosynthetic characteristics of transgenic rice with maize phosphoenolpyruvate carboxylase (PEPC) have been carried out. They show that such transgenic rice expresses high PEPC activity similar to that in maize (Chi et al 2001) and has better photosynthetic capacity with enhanced tolerance to photo-oxidation (Jiao et al , 2005, as compared with untransformed rice cv. Kitaake.…”

“…Kitaake. Use of radioactive methods proved that a greater amount of CO 2 was fixed in their primary C 4 photosynthates, indicating the existence of a primitive CO 2 concentrating mechanism (Jiao et al 2003). Moreover, the stable PEPC transgenic rice germplasm has been obtained by systematic selection and identification under natural conditions .…”

CO₂ sequestration in plants: lesson from divergent strategies

“…Also, the properties of PEPCase in C 4 plants are modified compared to the C 3 form, such that the mutants lacking it, are unable to assimilate atmospheric CO 2 (Dever et al 1995, Cholett et al 1996. Since PEPCase has a high affinity for CO 2 , overexpression of the enzyme is considered to be a promising approach to enhance the efficiency of carbon fixation (Miyao and Fukayama 2003, Jiao et al 2005, El-Sharkawy 2009.…”

“…Similarly, overexpression of PEPCase and PPDK in rice improved its photosynthetic capacity with enhanced tolerance to photo-oxidation and produced 22-24% more grains (Jiao et al 2002). Transgenic rice overexpressing PEPCase was shown to be more tolerant to photoinhibition that could improve protection from photooxidation (Jiao et al 2005, Zhang et al 2009). …”