Cloning And Analysis Of The Ainbino Cotyledons(al)Mutant Gene In Cucumber(Cucumis Sativus L.)

Leaf color mutants are mostly formed by silencing or inactivation of genes that control chlorophyll synthesis and chloroplast development,which directly or indirectly affect the synthesis and degradation of chlorophyll and lead to changes in leaf color.this study used a forward genetic approach to the phenotypic identification,gene mapping and gene function analysis of a cucumber(Cucumis sativus L.)whitening mutant albino cotyledons(al).The results show that:1.Cucumber al mutants are different from the reported cucumber leaf color mutants.After the seed germination of the mutant,the color of the unearthed cotyledons was light yellow,and then gradually completely albino.Cotyledon stage can grow normally and die before entering true leaf stage.The contents of chlorophyll a and chlorophyll b in the mutant were significantly lower than those of wild-type plants and chloroplasts could not be observed in cotyledon cells.The net photosynthetic rate was significantly lower than that of wild-type near zero,which resulted in the effects of photosynthesis could not maintain its normal growth;2.Provided glycogen culture to al mutants and found that the mutants could maintain growth on this medium.The content of reducing sugar and soluble sugar in cotyledon and true leaf of cucumber wild type(WT)was significantly lower than that of al mutant under the condition of sugar culture;3.Genetic analysis of al mutants showed that the phenotype was consistent with Mendelian gene-controlled genetic rule,indicating that albino traits were quality traits controlled by a pair of recessive nuclear genes.The al gene was located in the range of about 66 kb on chromosome 7 of cucumber by means of BSA mixing pool,molecular marker localization and genome sequencing.Ten genes were found to be related to chloroplasts by gene prediction function annotation analysis.It was suggested that Csa7G071680 might be a candidate gene for controlling albino traits and named Cs TIC21,The sequence and alignment Cs TIC21 wild-type and mutant gene coding regions revealed a single nucleotide mutation(G-T)in the fourth exon of the candidate gene,resulting in the change of the encoded amino acid from glycine to tryptophan;4.The function of the candidate gene Cs TIC21 was analyzed by VIGS technique.The homologous gene Nt TIC21 of the candidate gene was silenced in tobacco.The results showed that the new leaves of the silent plant yellowed relative to the wild type.It was speculated that the candidate gene Cs TIC21 related to chlorophyll synthesis and chloroplast development of the al mutant.Further study of the cucumber albino mutant showed that the expression of key genes regulating chlorophyll synthesis and chloroplast formation changed.These findings are helpful for further elucidating the regulatory mechanisms affecting chloroplast development of cucumber and are of great significance for studying photosynthesis mechanism,genetics and breeding.