Differential Proteomic Analysis Of Chloroplasts In Two Ecotypes Of Leymus Chinensis

According to the leaf color differentiation,Leymus chinensis is classified into two ecotypes as gray-green type(GG)and yellow-green type(YG).The GG and YG ecotypes display significant differences in photosynthetic physiological characteristics,and salt-alkali stress resistance,etc.However,the molecular mechanism of such differences remained to be elucidated.In this study,we used a proteomic approach to compare the chloroplast protein profiles,analyzed photosynthesis characterization of the GG and YG of Leymus chinensis,and the transcript levels of selected 9 protein-coding genes under salt and alkaline stress.1.The contents of chlorophyll a,chlorophyll b and chlorophyll a + b in leaves of GG was significantly higher than that in YG,but the chlorophyll a / b was the same between the two ecotypes.The diurnal variation of photosynthetic rate,transpiration rate and stomatal conductance of two ecotypes showed in a double-peak curve.The average daily photosynthetic rate and the photosynthetic rate at the time of 12 were significantly higher in GG than that in YG.Transpiration rate and stomatal conductance showed the similar between the two ecotypes,however,the transpiration rate at 12 and 14,and the stomatal conductance at 12 were markedly higher in GG than that in YG.2.The chloroplast from two ecotypes of Leymus chinensis was purified by Percoll density gradient,and the proteomic differences in chloroplasts were subjected to LC-MS/ MS based label-free quantitative proteomic analysis.In total,732 proteins were identified,57 of which were differentially accumulated proteins between two ecotypes of Leymus chinensis.Compared to YG,45 of the differential proteins were increased in in GG,whereas 12 proteins were decreased.3.Bioinformatic analysis showed that the functional categorization of identified differential proteins,including protein binding,transmembrane transport proteins,oxidoreductase activity,isomerase activity,transferase activity and hydrolase activity etc.The proteins involved in photosynthesis,protein localization,cell regulation,secondary metabolism,carbohydrate metabolism,etc.A protein-protein interaction network was generated using the STRING database.4.The 16 differential proteins were classified into seven metabolic pathways:(1)the photosynthetic pathway(8 proteins),including photosynthesis(PsbP,PsbQ,atpB,PsbB),photosynthetic antenna protein(LHCB1)and chlorophyll synthesis(HMBS,ChlM,FeCH);(2)the carbon metabolic pathways(MDH and rbcl);(3)Photosynthetic phosphorylation pathway(ndhB and atpB);(4)carotenoid synthesis pathway(LcyB);(5)redox proteins(Trx-m and PetH);(6)stress response(HSP70);and(7)signal recognition(SRP54).5.The results of qRT-PCR showed that selected 9 protein-coding genes of two ecotypes of Leymus chinensis had response to saline and alkali stress,however,the mRNA expression patterns differed.Changes in transcription level of candidate genes between the two ecotypes of Leymus chinensis suggested that may be related to the differentiation of the two ecotypes.These studies could provide insights into the molecular mechanisms of chlorophyll biosynthesis and photosynthesis alteration between the two ecotypes.