Genetic analysis and molecular characterization of a novel maize <italic>Bt2 </italic>gene mutant

Abstract

<p id="C3">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 <italic>5601Q</italic>, 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 <italic>5601Q</italic> 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 <italic>BRITTLE ENDOSPERM2 </italic>(<italic>Bt2</italic>) gene, previously reported to be involved in maize kernel development, was located in this region. Maize<italic> Bt2</italic> 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 <italic>5601Q</italic> decreased significantly, but the soluble sugar content increased dramatically 4.67 times. We confirmed that <italic>5601Q</italic> was a new allele mutant of <italic>Bt2</italic> by allelic test of <italic>Bt2</italic> mutant <italic>1774 </italic>and<italic> 5601Q</italic>. Sequencing analysis revealed that <italic>Mutator 19 </italic>transposon was inserted in the 2nd exon of <italic>Bt2</italic> gene. In summary, our results indicated that the shrunken kernel in <italic>5601Q </italic>was caused by the loss-of-function of <italic>Bt2 </italic>gene, which provided a new germplasm resource to elucidate the mechanism of maize <italic>Bt2 </italic>gene in endosperm storage substance accumulation.