Functional Analysis Of Lesion Mimic Gene Fd-GOGAT And Gene Mapping Of White Stripe Mutant K170 In Rice

This research contains two parts:The functional analysis of Fd-GOGAT and gene mapping of white stripe mutant K170 in Rice.Lesion is generated spontaneously in the absence of pathogen infection conditions in rice.The formation of lesion is closely related to the cell defense response,apoptosis and plant disease resistance.In the first part,the Fd-GOGAT gene has been previously isolated by map-based cloning from a spotted leaf 32(spl32)mutant.Based on this work,we did further research to find out the function of Fd-GOGAT in rice.Lack of Fd-GOGAT protein inhibited photorespiration and disturbed redox homeostasis in cells.The spl32 mutant appeared lesion because of oxidative stress.Results from our experiments were summarized as follows:1.Compared with the wild type,the spl32 mutant appeared necrotic spots on the five leaf stage and first appeared in the old leaves;then lesion began to spread the whole plants.From the tillering stage to the heading stage,lesion was even more serious.Chloroplast in the spl32 mutant was premature senescence and the formation of lesion was induced by light.Further,expressions of four pathogenesis-related(PR)maker genes were up-regulated and the enzyme activity of CAT and SOD were significantly increased in spl32 mutant.2.Fd-GOGAT,which caused the formation of lesion in spl32 mutant,was highly homologous to those in maize and sorghum and showed the highest expression level in the young leaves.3.Fd-GOGAT played an important role in photorespiration.GOGAT enzyme activity was decreased by 12.4%which caused the inhibition of photorespiration in spl32 mutant.Glycine from photorespiration was an important material for synthesis of glutathione(GSH),and then the synthesis of GSH was defected because of the reduced glycine content in spl32 mutant.GSH could scavenge oxygen free radicals in the cells,thus oxygen free radicals accumulated in spl32 mutant with the lesion mimic phenotype.4.Many amino acids were significantly decreased in spl32 mutant and this revealed that Fd-GOGAT plays an important role in amino acids metabolism.However,NADH-GOGAT2 played an important role in the non-photorespiration conditions.Then the expression of NADH-GOGAT2 was increased by 60 times than the wild type in spl32 mutant.Thus NADH-GOGAT2 could at least partially replace the function of Fd-GOGAT but is unable to completely replace Fd-GOGAT deficiencyLeaf is an exclusive place of photosynthesis in plants.Leaf color mutant in rice often leads to the chlorophyll content decreased and affects the synthesis and development of chloroplast.Thus it affects photosynthesis and crop yield.In the second part,the white stripes mutant K170 was used.We identified the genetic characteristic of the mutant phenotype in K170mutant and predicted candidate genes through fine mapping.The results were summarized as follows:1.Compared with the wild type,the mutant leaves showed white stripes in the seedling stage and turned green in the tillering stage.There are no normal chloroplasts and normal chloroplasts in K170 mutant through transmission electron microscopy.2.K170 was a single recessive gene.Molecular analysis of an F2 population and an F2:3 population from the cross K170 × Nanjingll(an indica rice variety)restricted the K170 locus between the InDel markers 3-21 and 3-22 on chromosome 3.Six insertion/deletion(InDel)markers were developed between these two markers.The K170 locus was further narrowed down to a 94-kb region,containing 8 putative open reading frames(ORF).3.The expression levels of photosynthetic system related genes were decreased but the expression levels of chloroplast synthesis related genes were increased in K170 mutant.