Characterization And Gene Mapping Of A Green-revertible Albino(Albg) Mutant In Rice(Oryza Sativa L.)

Leaf is one of the main plant photosynthetic organs,the changes of chlorophyll content,the morphology,structure and number of chloroplast affect the photosynthesis,leading to the reduction of yeild in rice.Therefore,leaf color mutants are important resources for researches about mechanism of leaf photosynthesis,development of chloroplast and metabolic pathways of chlorophyll.An albino mutant,named as albg,was obtained by the mutagenesis from Nipponbare using Ethyl Methane Sulphonate(EMS)treatment in the research.Identification and gene maping of the albg gene is valueable for better understanding of the genetic and molecular mechanism of the leaf color.The main results were as follows:1.Albino leaves appeared in albg mutant gradually turned green,when leaves fully expanded before the three-leaf stage,finally albino phenotype disappeared at the six leaf stage,and the albg mutant was obviously thermo-insensitive.Additionally,the content of chlorophyll a,chlorophyll b and carotenoid in the mutant were significantly lower than that of the wild type at the three-leaf stage,and the results were verified by the SPAD value.No significant difference was found in the chlorophyll content between albg mutant and wild type when it was the six-leaf stage.Moreover,microscopic observation revealed that the mesophyll cells of the mutant lacked intact chloroplast structure at the three-leaf stage.2.Compared with the wild type,setting percentage and plant heights were significantly reduced in albg mutant,as well as the grains per panicle.However,there was no obvious difference in 1000-grain weight and number of productive tiller between albg mutant and wild type.3.There were 439 wild type plants and 162 Green-revertible Albino plants in the F2 population crossed by albg mutant and Nipponbare cultivar.Genetic analysis indicated that the segregation ratio of the wild type and albg mutation was 3:1(?2=1.12<?20.05=3.84),suggesting that the albg mutation was controlled by a single recessive nuclear gene.4.The supposed recessive gene was mapped in a 163.1 kb region between InDel(insertion-deletion)markers 3G5 and 3G3 on chromosome 3 by map-based cloning.In this region there was 28 candidate genes.Of them,Os03g0597200 encoded a pentatricopeptide repeat(PPR)protein.Sequence analysis showed that there was a G insertion at the 1387th base pair from initiation codon in the exon of the gene.The results indicated that Os03g059720 could be the target gene.5.It was predicted that the albg contains six PPR motifs.Sequence comparison indicated that the mutation was caused by base G insertion,leading to the complete change of amino acids sequence and eventual loss of protein function.We also analyzed the evolution of PPR gene families in rice.