Fine Mapping and Identification of Ub4 As a Candidate Gene Associated with Tassel Branch Number in Maize (zea Mays L.)

The tassel branch number in maize is an important agronomic trait and it has been increasingly investigated in maize breeding programs. In this study, we isolated a pair of sister lines (Lx1 and Lx2) associated with the tassel branch trait. Lx1 showed unbranched tassel phenotype whereas Lx2 had 5–8 tassel branches. Genetic analysis showed that the unbranched tassel trait was controlled by a recessive gene designated as unbranched tassel 4 ( ub4 ). An F 2 population comprising 6782 individuals was developed to fine map ub4 . Finally, ub4 was mapped to an 88.2-kb region on chromosome 6, which harbored five candidate genes. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that the unique Zm00001d038546 gene in this region exhibited significantly different expression between Lx1 and Lx2. Sequence analysis of Zm00001d038546 from Lx1 showed that an 8-bp deletion in the third exon generated a premature stop codon, thereby leading to the termination of transcription. Moreover, Zm00001d038546 co-segregated with ub4 according to an InDel marker (InDel546) within the 8-bp deletion among the 1671 individuals without tassel branches in the F2 population. Therefore, Zm00001d038546 was considered as the most likely candidate gene for ub4 . These findings might be useful for reducing tassel branches and increasing grain yield in the maize breeding.