Physiological Characteristics Analysis Of Leaf Chlorosis Mutant Lcm4 And Mapping Of Mutant Gene In Chinese Cabbage

Chinese cabbage(Brassica rapa L.ssp.pekinensis)is a traditional and widely cultivated vegetable in China.Leaf is an important product organ and is also the main part for photosynthesis of Chinese cabbage.Leaf color is an important agronomic and commercial character of Chinese cabbage and the study on its leaf color has important theoretical significance and production value.Leaf color mutants have become important models for studying physiological and metabolic processes.lcm4(leaf chlorosis mutant 4)is a stably inherited leaf color mutant obtained by mutagenizing Chinese cabbage DH line 'FT' seeds with EMS.In this paper,the growth and development characteristics and photosynthetic physiological characteristics of lcm4 were analyzed,its genetic rule was clarified,and the candidate mutant genes were predicted.The main research results are as follows:1.Since the seedling stage,the yellow leaf mutant lcm4 showed obvious yellowing phenotype and showed yellowing during the whole growth period.Compared with the wild type 'FT',lcm4 can grow normally,but the dry weight at seedling stage was significantly lower than ‘FT',and the plant size was smaller.2.The content of photosynthetic pigments(Chla,Chlb,Car)in mutant leaves were significantly lower than those in 'FT'.The decrease of photosynthetic pigment has a certain effect on its photosynthesis.The main photosynthetic parameters(Pn,Gs,Tr)of lcm4 were lower than that of 'FT'.In addition,the decrease of main chlorophyll fluorescence parameters(Fo,Fm,Fo',Fm',Fv/Fm)indicates that the ability of light transfer and utilization of lcm4 was also affected.3.The ultrastructure of chloroplasts in leaves was observed by transmission electron microscopy.The chloroplasts in 'FT' leaves were normal in shape,well-structured and well-developed,while the chloroplast structure in lcm4 leaves was degraded,the thylakoid structure was impaired,the osmiophilic granules were increased,and the development of the whole chloroplast is hindered.4.Genetic analysis showed that yellow mutant trait was controlled by a single recessive nuclear gene(lcm4).Bra A01g009960.3C,encoding a Mg-chelatase I subunit,was predicted as a mutated gene by modified Mut Map method and KASP genotyping.There was a single nucleotide change on chromosome A01 at 5094365bp(C?T),resulting in early termination of translation.5.The transcriptomes of lcm4 and 'FT' leaves were deeply sequenced,and 105 differentially expressed genes(DEGs)were detected.A total of 13 GO terms and 2 KEGG Pathway were enriched.In addition,it was found that the pathways related to leaf color include porphyrin and chlorophyll metabolism,phenylpropane biosynthesis,plant hormone signal transduction,etc.Nine differentially expressed genes were selected for q RT-PCR,and the results of RNA-Seq were generally verified.