Genetic Analysis And Gene Mapping Of A Yellow-green Leaf Mutant Ygl10-2(t) In Rice

Rice(Oryza sativa L.)is the most important food crop in the world and provides food for more than half of the global population.With the increasing population of the world,the demand for rice yield is getting higher and higher.Photosynthesis is one of the key factors in determining yield level.Photosynthesis occurs mainly in the leaf organ and the photosynthetic efficiency is found to be largely affected by leaf color.Therefore,characterization and functional analysis for leaf color mutants are very important for us to understand the genetic mechanism underlying rice photosynthesis.In the present study,we characterized a yellow-green leaf mutant(temporarily named as ygll0?2(t))from an indica cultivar Shuhui 527 as genetic background.We performed genetic analysis,map-based cloning and functional analysis toward yg110-2(t).The results were as following:1.The phenotype observation and agronomic traits analysis showed that,the ygll0-2(t)mutant exhibits the yellow-green phenotype on the new leaf emerging since the 3?4th leaf stage,but truning dark gradually,similar with the wild type in terms of leaf colour.Agronomic traits investigation results indicated that most of agronomic traits significantly decreased,including but the length of the flag leaf,the width of the flag leaf,the number of primary branches,the number of secondary branches,the 1000-grain weight,the plant height,the number of full grains,the total number of grains and the seed setting rate,except for the number of main panicles and effective panicles,when compared to those of wild type.These results indicate that the mutation of ygll0-2(t)had a great effect on rice growth and development2.Photosynthetic pigment content measurements showed that,the total chlorophyll content and chlorophyll a,chlorophyll b and carotenoids of the mutants were statistically lower than the wild type at the whole growth duration.The total chlorophyll and chlorophyll a content decreased by 44.8%and 43.5%respectively,the chlorophyll b and carotenoids content decreased by 36%and 27.5%,respectively,at seedling stage.These results indicated that the synthesis of photosynthetic pigments was suppressed in the mutant3.The ultrastructural observation of chloroplast showed that,the chloroplast structure was abnormal and fewer number in the mutant,although some integral chloroplasts in few cells were observed.In addition,it was observed that the chloroplast in the mutant was irregular and the volume of chloroplast was slightly expanded with a less number of grana and irregular arrangement of layer.This indicates that the loss of gene function of YGL10-2(t)inhibits the normal development of chloroplasts.4.The fluorescence kinetics analysis showed that,in the mutant ygll0-2(t),the photochemical quenching(qP),non-photochemical quenching(NPQ),the actual photosynthetic efficiency of PS ?(Y II),and PS II electron transport rate(ETR)decreased by 12,1%,21%,28.4%and 28.7%,respectively,indicating that the mutation in YGL10-2(t)has the negative offect on plant photosynthesis with lower photosynthetic efficiency.5.Genetic analysis and gene mapping showed that,the phenotype of yellow green phenotype in the ygll0-2(t)mutant is controlled by a single recessive nuclear gene.The gene of YGL10?2(t)was located in a 104-kb region on the short arm of chromosome 10,suggesting it is a novel gene responsible for rice leaf color.6.Gene prediction showed that a total of 11 genes in the YGL10?2(t)anchored rangeand further sequencing results showed an 8-bp deletion occurred in thepromoter of LOC-Os10g10170 in the ygll0-2(t)mutant.It encodes encodes a pentatrioopeptide repeat(PPR)contyaining protein.The gene family is one of the largest families in plants,and is involved in the processing of organelles such as chloroplasts and mitochondria.Therefore,we tentatively designated the LOC-Os10g10170 gene as the candidate gene of YGL10-2(t).7.The expression pattern analysis was surveyed,the real-time PCR results that the LOC-Os10g10170 gene expressed in all tissues tested,with the highest level in leaves and with the lowest level in young panicles.However,the expression level in the mutant leaves was significantly decreased compared with the wild type.