Genetic analysis and molecular characterization of a novel maize Bt2 gene mutant

The research of the molecular mechanism underlying maize kernel development is particularly important for the genetic improvement of maize yield and quality traits. In this study, we characterized a new shrunken kernel mutant 5601 Q, which was generated by a random transposon insertion. Genetic analysis indicated that the kernel phenotype was stably controlled by a single recessive gene. F2 segregating population was constructed by crossing 5601 Q into B73 inbred line, and the mutant gene was located in the genetic interval of 60.19–62.58 Mb on chromosome 4. Sequence annotation showed that the BRITTLE ENDOSPERM2（Bt2） gene, previously reported to be involved in maize kernel development, was located in this region. Maize Bt2 gene encoded the small subunit of ADP-glucose pyrophosphorylase（AGPase）, the first rate-limiting enzyme in the starch biosynthetic pathway of higher plants. Compared with wild type, 100-grain weight and starch content of mutant 5601 Q decreased significantly, but the soluble sugar content increased dramatically 4.67 times. We confirmed that 5601 Q was a new allele mutant of Bt2 by allelic test of Bt2 mutant 1774 and 5601 Q. Sequencing analysis revealed that Mutator 19 transposon was inserted in the 2 nd exon of Bt2 gene. In summary, our results indicated that the shrunken kernel in 5601 Q was caused by the loss-of-function of Bt2 gene, which provided a new germplasm resource to elucidate the mechanism of maize Bt2 gene in endosperm storage substance accumulation.