Comparative Proteomic Research Towards Molecular Basis Of Heterosis In An Elite Rice

Heterosis is a fundamental biological phenomenon,refers to the superiorperformance of hybrid in terms of increased yield,quality,growth vigor,speed ofdevelopment and resistance to climatic rigours relative to both parent lines.Theapplication of heterosis to agriculture has produced enormous social and economicbenefit,but the mechanism underlying heterosis remains elusive.Recently,manyresearches focus on the molecular basis of heterosis,several studies analyzed heterosisassociated gene expression pattern at the mRNA translation level,and nonadditive geneexpression was found in hybrids of different plants.But few studies were carried out at theprotein lever.To study gene expression pattern of hybrid rice at protein level,theproteome of embryo,leaf and root from an elite hybrid rice Shanyou63 and its parents wasanalyzed with 2-DE or DIGE,MALDI-TOF-MS and MALDI-TOF-MS/MS.Embryo proteins in mature seeds of elite hybrid rice shanyou 63 and its 3-lines(sterile line,maintainer line and restorer line) were separated with 2-DE.The number ofdetected protein spots was 965.7±19.2 (SD,n=3),964.7±16.7,961±18.7 and 982.7±19(n=6),from Zhenshan97A (sterile line,female parent),Zhenshan97B (maintainer line),Minghui63 (restorer line,male parent) and Shanyou63 respectively.No repeatabledifference was detected between Zhenshan97A and its isogene line Zhenshan97B.However,there were many differentially expressed proteins between Zhenshan97A andMinghui63,showing 19 reaptably differential protein spots detected only in Zhenshan97A,and 17 ones only in Minghui63.All of these differential proteins were expressed in hybrid.Furthermore,there were 21 protein spots with different abundance in parents.It isremarkable that the abundance of all those differentially expressed proteins in the hybridwere different from that of corresponding proteins expressed in its parents,and main ofthem were close to the mid-parent values,although some of them deviated relativelymid-parent predictions,exhibiting somewhat nonadditive expression.20 differentiallyexpressed proteins were analyzed through MALDI-TOF-MS/MS and database searching.Of the 9 identified proteins,dihydrolipoyl dehydrogenase and putative phosphoglyceratemutase involved in respiration metabolism,chitinase correlated to disease and defend, and others were putative globulin and putative LEA domain-containing protein.Morphological traits of aerial part in Shanyou63 and its parents was surveyed,different midparent heterosis(MPH) was found in plant height,leaf length and leaf wide atseedling stage,only leaf area showed a significant best parent heterosis(BPH) of 15.72 %.It suggested that multiplicative effect is a important factor in the formation of BPH of leafarea.Differentially expressed leaf proteins among the three lines were examined usingDIGE.Of the＞1677 protein spots reproducibly detected on each gel,23 protein spotswere found different accumulation among the three lines (ANOVA-1 analyzed,p＜0.01).Inthe hybrid,16 proteins were accumulated in a additive fashion in the hybrid compared tothe average of their parental lines,while the standard volume of 2 proteins showed anonadditive expression＞20%,while the other 5 protein spots showed a nonadditive withina range of 10-20%.22 of the differentially expressed proteins were identified by MALDI-TOF-MS anddatabase searching,included 2 respiration metabolism proteins,dihydrolipoyldehydrogenase and putative phosphoglycerate mutase;a ferredoxin--NADP reductaserevolving in photosynthetic electron transport chain;a Putative 3-beta hydroxysteroiddehydrogenase/isomerase may be an enzyme in steroid metabolism;a RPS5 containingprotein may revolve in gene expression and regulation;and 3 anti-oxidatant enzymes:GSH-dependent dehydroascorbate reductase 1,peptide methionine sulfoxide reductaseand a putative peptide methionine sulfoxide reductase.Differentially expressed root proteins among the three lines were examined with 2-DEand CBB staining。23 protein spots were found different accumulation among the threelines (Student's t-test,p＜0.05),4 of them showed a nonadditive expression＞20%,noprotein was found specially expressed in hybrid,but spot 19 showed a obvious decreasein F1.Using MALDI-TOF-MS/MS and database searching,all of the differentially expressedroot proteins were identified.8 of them was manifested involving in matter and energymetabolism,while 2 were related to signal transduction,and a kelch repeat containingprotein might involve in protein-protein interaction,possible related to epistasis. The puzzle of why dominance or over-dominance hypothesis cannot explain theheterosis mechanism properly was discussed.It is considered that global heterosis,suchas heterosis of yield,dose not necessarily be the result of local heterosis which could beexplained fully by these hypothesis.It is proposed that,among the local traits,there is amultiplicative relationship by which the heterosis of local traits was organized to formglobal heterosis.It is hold that multiplicative relationship and multiplicative effect wereimportant basis of global heterosis,and then some conclusion concerning breedingpractice were deduced.