The Molecular Mechanism Study On Chlorophyll Synthesis In The Yellow Leaf Rice

The polymorphism of plant leaf color has been widely applied in the field of garden aesthetics.Recently,field pictures which consist of a variety of leaf colors have become one of the hot spots in the area of sightseeing agriculture.The technique,with the leaf color used as a marked character in the hybrid rice male sterile lines,may become an important part in hybrid seed production during the current hybrid rice breeding realm.Its significance lay in the following aspects:first,in the preparation of hybridization breeding,the contaminating plants of non-male sterile lines can be removed from the rice nursery in the period of seedling based on the different leaf colors.Second,after the rice transplanting in the seed field,the seedling of shattering grain from the previous quarter could be identified in the period of seedling,which could eliminate the heavy work of removing the impurity in the male sterile line in the heading and flowering period,as well as improve the purity of the hybrid seeds.The rice sterile line KT27S with yellow leaf developed in our laboratory,is the first thermo-sensitive male sterile line approved by Hunan province.According to the previous studies,the male sterile line could grow normally.Meanwhile,in the condition of strong light,it can maintain higher photosynthetic rate than the normal green leaf rice without light saturation point or midday depression.The feature of pale yellow leaf was due to 50%decrease in chlorophyll content than that of the normal leaf.Nevertheless,the molecular mechanism of the decrease of chlorophyll content in yellowish male sterile line is still confusing.In this paper,we studied the biochemical mechanism of decrease in chlorophyll content and the change of the related genes with the yellow leaf KT27S as the experimental group while the H628S set as the control group.The aim of this study is to reveal the molecular mechanism of yellow leaf and promote its application.The main results are as follows:1.Based on the comparative analysis of the content of precursor substances in the pathway of chlorophyll biosynthesis,we may find that the content of ProtoIXfrom the yellow leaves much higher than the normal leaf.While the Mg-Proto,and the subsequent synthetized Pchlide,Ch1 a and Ch1 b are much lower than the normal group.As described in our survey,the key enzyme resulting in the reduction of chlorophyll synthesis in KT27S is the Magnesium chelatase,which may turn the protoporphyrin IX into magnesium protoporphyrin.2.The activity of magnesium chelatase in KT27S was 5.65 times lower than that of the control,the wild group(H628S).3.Magnesium chelatase is composed of three parts,the D,I,H subunit.Based on the gene cloning and sequencing of these 3 subunits,the Thymine in the 1883rd position of the D subunit mutated to Cytosine.While the amino acid L628 changed to S628.Furthermore,there are obvious changes insecondary structure from the D sub-unit.This conformational transition may impair activity of Magnesium chelatase to convert the ProtoIX into Mg-Proto.According to our survey,the molecular mechanism the yellow leaf is that the Thymine in the 1883rd position of the D sub-unit of the magnesium chelatase mutated to Cytosine.While the amino acid L628 changed to S628.This conformational transition may impair the activity of Magnesium chelatase to convert the Proto?into Mg-Proto and eventually results in decrease in chlorophyll biosynthesis.