Physiological Characteristics And Candidate Genes Analysis Of Leaf Late Etiolation Mutant Lle Of Rice

Rice is one of the main food crops in China,more than 50%of my country’s population feeds on rice as the staple food.Therefore,the increase in rice production can well solve the problem of food security in my country.Leaf is an important place for rice photosynthesis.About 90%of the yield of rice is determined by the photosynthesis capacity of the leaves,Leaves play an important role in the growth and development of rice.Therefore,the use of rice leaf color mutants to study the regulation and molecular mechanisms of photosynthetic pigment synthesis and metabolism and photosynthesis is of great significance for promoting rice variety improvement and high and stable yield.In this study,a leaf late etiolation mutant（lle）was obtained from the natural variation of Dongjing japonica rice and named as leaf late etiolation mutant（lle）.The phenotype,photosynthetic characteristics,physiological characteristics,cytological level and BSA sequencing of the lle mutant lle were determined and analyzed.The main results are as follows:（1）The yellow leaf phenotype of the leaf late etiolation mutant（lle）appeared at the seedling stage.The yellowing of the leaves in the middle and late stages became more and more obvious,and the degree of yellowing of the leaves in the late stage was significantly different than that of the wild type（WT）.According to the results of the photosynthetic pigment content,the total chlorophyll content of the leaf late etiolation mutant（lle）was reduced by 8.25%,17.32%and 34.31%in the early,middle and late growth stages,respectively,compared with the WT.The difference between the two is extremely significant.Compared with the WT,the total amount of chlorophyll in the three parts of the mid-term mutant（lle）first leaf,second leaf and third leaf was extremely significantly reduced;compared with the WT,the lle mutant first leaf and second leaf had a significant decrease in total chlorophyll.Chl a/b increased compared with the WT,and the difference was extremely significant.（2）The measurement results of chlorophyll fluorescence kinetic parameters showed that the maximum photochemical efficiency（Fv/Fm）,photochemical quenching coefficient（q P）and fluorescence quantum yield（Yield）of the lle mutant were not significantly different from the WT,but not the photochemical quenching coefficient.（NPQ）and electron transfer rate（ETR）are significantly higher than the WT.According to the results of photosynthesis parameters,the net photosynthetic rate（Pn）,stomatal conductance（Gs）and transpiration rate（Tr）of the lle mutant were reduced by 7.6%,17.74%and 27.94%,respectively,compared with the WT.The difference was extremely significant.The intercellular CO₂concentration（Ci）of lle is higher than that of the WT,but the difference is not significant.（3）The protective enzyme activity results showed that the protective enzyme activities such as superoxide dismutase activity（SOD）,peroxidase activity（POD）and catalase activity（CAT）of the lle mutant increased by 12.13%and 38.85%,respectively And 8.51%,the MDA content increased by 11.58%,both showing a significant difference.（4）Observed by transmission electron microscope,the chloroplasts of the lle mutant are irregular in shape,and the number is reduced to a certain extent,the thylakoid structure is not clear,the arrangement is loose and irregular,and there are many more osmophiles.The analysis of agronomic traits showed that the plant height,effective ear number and grains per ear of the lle mutant were reduced by 14.74%,13.73%and 23.93%respectively compared with the WT,which was extremely significant;in terms of ear length,it was reduced compared with the wild type.16.38%,the difference is significant;there are differences in other agronomic traits,but the difference is not significant.（5）Genetic analysis showed that the later leaf yellowing traits are controlled by a pair of recessive nuclear genes.According to the results of BSA sequencing analysis,the amount of effective data obtained by sequencing the four samples is sufficient,the sequencing quality is high,and the GC distribution is normal.The comparison rate of the four samples is between 97.08%～99.51%,the average coverage depth is between24.52X-28.19X,and the 1X coverage is above 91.77%.Based on the algorithm of SNP-index and In Del-index,the target interval is finally located on chromosome 8,which contains a total of 15 candidate genes.According to ANNOVAR’s annotation analysis,we speculate that the gene LOC＿Os08g17080 involved in encoding the PPR repeat domain protein on chromosome 8 is a candidate gene,which may be a new leaf yellowing mutant gene.