Gene Mapping And Functional Analysis Of Maize Albino Mutant

As an important food and cash crop in the world,Maize（Zea mays L.）is widely used in feed,processing and food industries.In recent years,corn production in China has been hovering around 270 million tons,to further increase the yield to meet the growing market demand,still need to strengthen scientific and technological innovation to support,so how to improve the corn yield related research is very important.As the unique photosynthetic site of green plants,chloroplast is an important place for the synthesis of starch and sugar.The abnormal development of chloroplast structure will seriously affect the photosynthetic efficiency,and even cause the complete loss of photosynthetic capacity.In this study,a novel maize albino（alb）mutant was isolated and identified from maize B73 EMS mutagenic mutant library,and the preliminary gene mapping and functional analysis of alb mutant were carried out.The specific research contents and conclusions are as follows:1.The phenotype identification and genetic analysis results of alb showed that the phenotype of alb was complete albino at seedling stage and gradually died after growth to trifoliate stage.In the middle stage of growth,some plants of the F₂segregation population of alb showed white-green variegation phenotype.Compared with B73,the chlorophyll contents were extremely significantly reduced,and almost no chlorophyll a（chl a）and chlorophyll b（chl b）were detected in alb.In addition,F₂segregation population of alb existed a ratio of green seedling:albino seedling=3:1,indicating that the albino phenotype of alb was caused by a single recessive nuclear gene mutation.2.Gene mapping of alb was performed by MutMap method,and the result shown that the coding sequence of Zm00001eb049810（Zm MGR5）existed c.1022T>A|p.Met341Lys non-synonymous mutation,and Zm MGR5 was the candidate gene to control albino phenotype of alb.A Zm MGR5 allele mutant mgr5-1（c.1582C>T|p.Gln528*）from Maize EMS Mutagenic Mutant Database（MEMD）was used to perform the identification of genotype and phenotype,the results showed albino phenotype and white-green variegation phenotype were isolated from mgr5-1,and albino genotype was mgr5-1-/-,the white-green variegation genotype was mgr5-1+/-.3.ZmMGR5 encodes a Mg²⁺transporter with transmembrane domains and a pair of CBS domains which are the typical domains of the MGRs family of proteins.Phylogenetic analysis and sequence alignment showed that the sequences of MGR5protein were highly conserved,and the methionine at position 341 of ZmMGR5protein was completely conserved among plant species.The subcellular localization result showed that Zm MGR5 protein was localized on the chloroplast.The tissue-specific expression analysis of Zm MGR5 showed that Zm MGR5 was widely expressed in maize tissues,and the highest expression was found in leaves.However,the expression of Zm MGR5 in leaves did not change significantly under Mg²⁺deficiency condition,indicating that Zm MGR5 was not stimulated by the external low Mg environment.The result of electron microscopy showed that chloroplast development and biogenesis were seriously affected in the mesophyll cells of alb.Compared with B73,there was no complete chloroplast in the mesophyll cells of alb,including chloroplast membrane and thylakoid.4.Transcriptome sequencing was performed on the leaves of alb and B73,and GO and KEGG enrichment analysis of differentially expressed genes was carried on.The results suggested that in cellular component the chloroplast membrane including chloroplast envelope and thylakoid membrane related genes,were significantly down-regulated in alb.Genes involved in photosynthesis-related pathways including LHCs,photosystemⅠ,photosystemⅡ,photosynthetic electron transport chain and carbon fixation were significantly down-regulated.The expression of genes involved in the downstream pathways of photosynthesis,such as starch and carbohydrate metabolism,was also significantly down-regulated in alb,indicating that chloroplast development,photosynthetic pathway and a series of other reactions in chloroplast were seriously affected in the alb.In addition,genes related to plant hormone metabolism and signal transduction pathway,such as cytokinin and auxin,which are involved in chloroplast development,are down-regulated,thus affecting chloroplast development.In conclusion,this paper conducted a detailed study on a new maize albino mutant,and the candidate gene of albino phenotype was identified.the enriched pathways of differentially expressed genes were identified in alb through transcriptomics,which laid a theoretical foundation for further research on the development mechanism and gene regulation of chloroplast.