Analysis Of Yellowing Mechanism Of Yixuan Dahongmei Mutant YX-yl

Chlorophyll is the main pigment of photosynthesis.The changes of chlorophyll content directly affects the leaf color,which is associated with crop yield.In this study,the yellowing mutant YX-yl,mutated by EMS chemical mutagenesis,was analyzed from the aspects of agronomic traits,pigment contents,chloroplast ultra structures and chlorophyll precursors.Furthermore,the yellowing mechanism was also studied by transcriptome sequencing at the molecular level.The main results are as follows:The yellowing mutant YX-yl is a short plant with slender stem and lower yield.During the whole growth period,the leaves of the plant showed a yellow-green phenotype and poor photosynthetic capacities.The content of chlorophyll a,chlorophyll b and the carotenoids in leaves of YX-yl were less than the contents of wild type.The results of chlorophyll precursors analysis showed that the chlorophyll biosynthesis in YX-yl was hindered by the step of which porphobilinogen conversing to protoporphyrin IX.Through observing the ultra structure of chloroplasts in leaves,it was found that the chloroplasts of YX-yl were accumulated at one end of the cell.In addition,the chloroplast structure of YX-yl was obviously degraded.The whole chloroplast structure was blurred,and the chloroplast membrane could not be clearly identified.The number of grana in the chloroplast was small and scattered,and the number of matrix lamellae constituting the grana was also small.The transcriptome of the yellowing mutant YX-yl was sequenced and compared with the wild type.Nine chlorophyll-related genes with significant different expressing profiles were selected,which were c59782.graph_c1,c58359.graph_c0,c60440.graph_c0,c60651.graph_c0,c61687.graph_c1,c61835.graph_c0,c61963.graph_c0,c64963.graph_c0 and c65342.graph_c0,respectively.These genes are located in chloroplast,chloroplast membrane,chloroplast thylakoid membrane and chloroplast matrix,and mainly involved in chlorophyll biosynthesis and the regulation of its redox-related enzymes.Based on the above results,it was hypothesized that the different expression of some genes between the yellowing mutant YX-yl and the wild type led to the changes in the chloroplast structure and the activities of some enzyme in chlorophyll synthesis pathway.Finally,it led to a yellowing phenotype in mutant YX-yl that has lower chlorophyll contents.