Phenotypic characterization and genetic mapping of the dwarf mutant m34 in maize

Plant height is one of the most important agronomic traits associated with yield in maize. In this study, a gibberellins (GA)-insensitive dwarf mutant, m34, was screened from inbred line Ye478 by treatment with the chemical mutagen ethylmethanesulfonate (EMS). Compared to Ye478, m34 showed a dwarf phenotype with shorter internodes, and smaller leaf length and width, but with similar leaf number. Furthermore, m34 exhibited smaller guard cells in internodes than Ye478, suggesting that smaller cells might contribute to its dwarf phenotype. Genetic analysis indicated that the m34 dwarf phenotype was controlled by a recessive nuclear gene. An F₂ population derived from a cross between m34 and B73 was used for mutational gene cloning and this gene was mapped to a chromosome region between umc2189 and umc1553 in chromosome 1 bin1.10, which harbored a previously identified dwarf gene ZmVP8. Sequencing analysis showed a nucleotide substitution (G1606 to A1606) in the sixth exon of ZmVP8, which resulted in an amino acid change (E531 to K531) from Ye478 to m34. This amino acid change resulted in an α-helix changing to a β-sheet in the secondary protein structure and the ‘SPEC’ domain changed to a ‘BOT1NT’ domain in the tertiary protein structure. Taken together, these results suggested that m34 is a novel allelic mutant originally derived from Ye478 that is useful for further ZmVP8 functional analysis in maize.