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Plant height is an important index for the ideal maize breeding, which not only affects the mechanical harvest of maize, but also closely relates to the lodging resistance and the biological yield of maize. In this study, a plant height reducing mutant-1 (phr-1) was obtained by using low-dose fast neutron (4.19 Gy) irradiation to mutate the maize inbred line KWS39 at the low ear position. Phenotypic traits were investigated and analyzed in the field, and candidate genes were identified by mining and functional annotation of genes in the target region based on the B73 reference genome using the extreme trait pool sequencing analysis (BSA-seq) and the method of target region recombination exchange identification with F2 segregation population of phr-1xB73. These results indicated that there might be a variation site in Bin1.06 interval on chromosome 1, and the target region was precisely located between two markers, Umc1122 and Umc1583a, with a 600 kb interval by using the large segregation population and polymorphic markers. Brachytic2 (BR2), encoding a sugar protein regulating the polar transport of auxin in maize stems, is a known gene controlling plant height in this region. The sequencing of candidate genes revealed that phr-1 was a new allelic mutation of br2-1, with a 165 bp insertion in the fourth exon of the BR2 gene resulting in the amino acid at position 547 changing to a stop codon and premature protein translation termination. The mutation site and variation mode of phr-1 were completely different from those of br2-1 single base mutation site. The allelic hybridization experiment confirmed that the PHR1 candidate gene is a new allelic mutation of the BR2 gene. This study provides new germplasm resources for maize BR2 gene in plant height genetic improvement. [ABSTRACT FROM AUTHOR]

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