Map-based Cloning And Functional Analysis Of The Rice Mutant Gene OsPPR3Controlling White Stripes Leaf

Leaf colour mutants are ideal materials for the studies of chlorophyll biosynthesis andregulation mechanism, photosystem structure and function. It also has been widely used inhybrid rice as a trait marker．In this study, we identified a radiation-induced mutant fromindica rice cultivar,93-11, designated Osppr3, which exhibits White Stripes leaf phenotypeand on the basis of its phenotypic analysis, some studies were done in physiology and cellmorphology. Through a map-based cloning approach, the OsPPR3gene was isolated the mainresults were as follows:1. Under natural condition, the mutant Osppr3showed the white stripes only at the initialthree leaves and exhibited normal leaves from the four-leaf stage. Additionally, the content ofchlorophyll a, chlorophyll b and β-carotenoid was significantly lower at the white stripeleaves of the mutant than that of the wild type, but the ratio of chlorophyll a to chlorophyll bwas similar. Moreover, microscopic observation revealed that the cells within the white stripeslacked intact chloroplast structure.2. Genetic analysis indicated the mutant was controlled by a single recessive nucleusgene. To map the target gene, we generated F2mapping population derived from a cross of theOsppr3mutant and cultive“ReYan2”. We mapped the mutants gene to an interval betweenmarkers LS01（9cM） and LS11（1.2cM）on Chromosome1. To narrow down the search fora candidate gene affected in Osppr3, a larger F2mapping population were used forfine-mapping. Finally the target gene locus was located in a79kb DNA region on a singleBAC, B1064G04. There are5genes code were predicted in the website. Comparison of thesequences revealed that only the gene Os01g37870have a mutantion,6bases deletion aboutcDNA sequence, which results in two conservation amino acids（Alanine and glutamic acid）.Therefore, we tentatively designated the Os01g37870（named OsPPR3）as the Osppr3gene.3. Complementary experiment revealed introduction of exogenous OsPPR3into theOsppr3can restore the phenotype of mutant and OsPPR3gene located at the chloroplast PPRdomain had a high degree of identity among species. Expression analysis showed the normallevel of OsPPR3gene in the mutant. However, the gene rbcL, which affecting chlorophyIIsynthesis and development of chloroplast,and the gene psaA（A1）, encoding a reaction centerprotein, had been impacted and influenced to some extent. Futhermore, Osppr3exhibitedhypersensitivity to ABA and Nacl concentrations, suggesting the possible roles of OsPPR3gene in regulation of Nacl and abscisic acid signal transduction.