Development Of Plant Mutants Based On MNU Mutagenesis Of Pollen Germ Cells Of Maize And Characterization Of Their Characters

Maize(Zea mays L.)is a major food crop and is widely used in many fields such as agriculture,feed and energy.With the shift of life sciences to the era of post-genomic researches,maize sciences has begun to enter the functional genomic studies for revealing the expression of functional genomes and their mechanisms regulating characters,the cultivation of maize cultivars is also tending to achieve diversified breeding objectives.Researches for maize genome have shown that there are about 32,000 genes in maize.For a long time,the development and utilization of maize mutants have promoted the identification and functional analysis of some genes,but the biological functions of most maize genes are still unknown.One of the main reasons resulting in this situation is the insufficiency of genic-mutant materials due to the lower efficiency of maize mutagenesis.In recent years,the technology for N-methyl-N-nitrosourea(MNU)mutagenesis on the mature pollen germ cells of maize has been established in our laboratory.The mutagenesis technology in our laboratory has the significantly improved efficiency of broad-spectrum induction of genic mutations,compared with the reported ethylmethylsulfone(EMS)mutagenesis on maize.Expressions of plant types characters in maize carry the basic functions for morphogenesis and biological-yield formation of maize.About 400 functional genes regulating the expressions of plant characters in maize have been registered in the Maize Genetics and Genomics Database(https://www.maizegdb.org).In order to provide the various genic-mutant materials for identifying the unknown genes regulating the expressions of plant characters in maize,in this study,33 maize mutants including lethal seedling,culm,leaf and spike types of mutants were created,and 16 homozygous mutants(named ZMPM series)were obtained and characterized,screening characters of the M2-M3 plant populations derived by the MNU treatment of pollen germ cells of the wild type maize inbred line,A378.Compared with the A378,the homozygous mutants showed various alterations characters for plant appearance,tissues and cells.The ZMPM1,a tillering mutant,showed the attributes including the double-branch tillering,internode number reduction,dwarfing,stem coarsening,leaf widening,densification of thick wall cells of internode,ear minifying,growth period extension.The ZMPM2,ZMPM3,ZMPM4,ZMPM5,ZMPM6,ZMPM7 and ZMPM8 all were all the significantly dwarfed mutants with single,showing the attributes including the decreased number and length of internodes,internode cells flattening and ear height reduction;among them,ZMPM2 also has the characteristics of ear size and 100-grain weight increase,while other dwarfing nutants had smaller ears but had no significant effect on 100-grain weight.The ZMPM9,ZMPM10 and ZMPM11 were the thin culm mutants,showing the attributes including the diameter decrease and number increase of vascular bundles,and the smaller ears.The ZMPM12,ZMPM13,ZMPM14,ZMPM15 and ZMPM16 were the mutant with small leaf angles,showing the attributes including the significant decrease of leaf opening,increase of parenchymal cell layers in mesophyll,enlargement of large vascular bundles in leaf veins,and extension of growth period.The other 17 mutant lines showed mainly returning wild type,seedling lethality,abnormal tassels or non-single gene types mutations;among them,the mutant lines of seedling lethality and abnormal tassels can only exist in heterozygous genotypes,and the characters of non-single gene types mutant lines need to be homogenized through phenotypic isolation of the next generation.Among the mutants obtained in this study,the thin stem mutants are the novel type mutant materials not been reported,and the tillering,dwarfing and small leaf angle mutants have the novel characteristics of appearance or histiocytes of plants.In the future,the mutants can be applied to the maize researches for genetics and breeding including genetic analysis,proteomic characterization,transcriptome or c DNA identification,gene cloning or coding protein analysis and new variety cultivation.Their application isexpected to promote the identification of unknown functional genes regulating plant character expression in maize,and the cultivation of high-yield maize varieties with lodging resistance,dense-planting tolerance and mechanical adaptability.