Inducement And Identification Of An Endosperm Mutant In Maize

Physical and chemical mutagenesis has been proved to be effective in inducement of useful mutants with novel gene alleles and increase of genetic diversity for enrichment of ger/minlasm resources in crops. However, the low mutagenesis frequency along with limited desired mutants for selection has greatly affected its application, especially that mutagenesis is usually used to treat mature seed. Induced mutagenesis is a random process, and it is rather difficult to screen the desired mutants, without precise information at the molecular level for phenotypic changes. On the other hand, the recent advances of plant molecular genetics and functional genomics have facilitated screening and identification for the desired mutants.To screen a workable dosage combination of gamma-ray and NaN3 for mutation inducement, maize calli were treated with different dosages of 60Co gamma-ray and NaN3. The results indicated that the combination of 20 Gy of gamma-ray and 1 mmol/L of NaN3 is the most effective for mutation inducement of maize calli.Three endosperm mutant lines with " super sweet" phenotype were derived from the mutated offspring. To identify the probable mutated gene of the endosperm mutant lines by complementation test, straight and reciprocal crosses were made between the homozygous M5 plant lines of mutants "sm-1", "sm-2" and "sm-3", and the inbred lines with sweet genotypes susu (sweet), sh2sh2 (super sweet), btlbtl (brittle sweet) and bt2bt2 (brittle sweet), respectively. The results of the complementation test showed that the mutations in mutants "sm-1", "sm-2" and "sm-3" are probably involved in gene sh2.By DNA sequence analysis, their mutation site was found involved in exon 14 of gene sh2, that encodes adenosine diphosphate glucose pyrophosphorylase. For their highly consistent phenotypes of agronomic characteristics, and distinguished molecular mechanism to the previous mutants of gene sh2, these three mutant lines are regarded as a novel multiallelic mutant of gene sh2.Complementation test has been widely used in microbial genetics to determine whether two recessive mutations take place in the same gene (cistron). In higher plants, this simple method has been seldom used because it is usually unavailable to find appreciate mutations complementary to the mutant to be identified. For endosperm mutations in maize, however, a wide spectrum of different endosperm mutations have been collected. It is helpful to screen preliminary candidate site for random mutagenesis by complementation test before complicated molecular procedures.