Overexpression Effects Of Rice Rubisco Activase (OsRCA) On Rubisco Activity Sate And Photosynthesis In Maize

Maize is one of the most important food crops.Improving the utilization rate of maize light energy is of great significance to increase maize yield,meet market demand and ensure food security.Ribulose 1,5-bisphosphate carboxylase/oxygenase(Rubisco)is a key enzyme in photosynthetic carbon assimilation,and increase Rubisco activity can be an option to improve photosynthetic efficiency in C4 crops.Rubisco activase(RCA)can regulate the Rubisco activation state,influencing Rubisco activity and photosynthetic rate.However,the expression level of RCA in C4 maize was lower than that in C3 rice,and the affinity and specificity of Rubisco for CO2 was lower than that in rice.The aim of this study was to overexpress rice RCA(OsRCA)in maize to improve the activity of maize Rubisco and to analyze its effect on maize photosynthesis.The main results are as follows:1.The full-length cDNA of OsRCA was cloned from rice leaves(Oryza sativa L.ssp.japonica).OsRCA was connected to pCAMBIA3301-GFP vector driven by 35S promoter.We introduced the overexpression vector into maize inbred line B104 by Agrobacterium-mediated method.Three representative OsRCAOE lines(OsRCAOE2,OsRCAOE5 and OsRCAOE9)were screened out by PCR,qRT-PCR and Western-blot for subsequent study.2.The Rubisco activity of B104(WT)and OsRCAOE lines was determined.The results showed that the Rubisco initial activity and activation state of maize were enhanced after OsRCA overexpression,but the total activity was not significantly different.Meanwhile,Western blot and ELISA showed that OsRCA overexpression had no effect on the maize Rubisco content.3.The OJIP curve,820 nm reflection kinetics and delayed fluorescence analysis showed that there was no significant difference between WT and OsRCAOE lines,indicating that OsRCA overexpression did not significantly change the electron transport capacity of PSII and PSI on the acceptor side and the donor side,and the REDOX state of PSI under the light reaction of maize.The results of gas exchange parameters showed that,compared with WT,OsRCA overexpression enhanced the net photosynthetic rate of maize plants(Pn).Meanwhile,the fluorescence quenching and PSⅡ and PSⅠ energy conversion-related parameters of WT and OsRCAOE lines were analyzed.The results showed that,compared with WT,the photochemical quenching qP and PSⅡ photochemical energy conversion yield[Y(Ⅱ)]of OsRCAOE lines increased,while quantum production of non-regulatory energy dissipation at PSII[Y(NO)]decreased,indicating that OsRCA overexpression enhanced the photochemical efficiency and photoprotection of PSⅡ and inhibited the passive energy dissipation of maize.