Objective By detecting the natural variation of Auxin Up-regulated F-box protein2 (AUF2) gene and exploring the elite alleles associated with agronomic traits in order to provide theoretical references for molecular marker assisted breeding of flowering Chinese cabbage.

Method PCR amplification and sequencing was used to detect the natural variations in AUF2 gene among 156 flowering Chinese cabbage accessions. By using the mixed linear model (MLM) of Tassel 5.0 software, the correlation between the variation sites of AUF2 gene and six agronomic traits of flowering Chinese cabbage was analyzed, including plant height, single plant weight, maximum leaf length, maximum leaf width, maximum petiole length and chlorophyll content (SPAD), and the polymorphic sites significantly associated with agronomic traits would be identified. Then, elite alleles and excellent haplotypes were determined.

Result Through sequencing analysis, a total of 34 mutation sites were detected in the 2 996 bp amplification region of AUF2 gene, including 36 haplotypes. The AUF2 gene showed high nucleotide diversity (π = 0.00503) and haplotype diversity (Hd = 0.780). Among them, 2 InDels and 26 SNPs were in the 1 498 bp upstream non-conding region, and 1 InDel and 5 SNPs were in the 960 bp coding region. No mutation sites were detected in the 538 bp downstream non-conding region. Neutral test analysis showed that Tajima's D value, Fu and Li's D^* value, and Fu and Li's F^* value of the AUF2 gene were positive, and deviated significantly from neutral evolutionary model. One plausible reason was that flowering Chinese cabbage population was subject to balancing selection. The association analysis showed that 4 SNPs were significantly associated with at least one of the four agronomic traits, including single plant weight, maximum leaf length, maximum leaf width and maximum petiole length. The phenotypic variation of a given trait explained by each associated SNP ranged from 5.04% to 6.52%. The haplotype Hap2, which contained elite alletes of the four SNPs mentioned above, could significantly raise the single plant weight, and remarkably increase the length of the maximum petiole.

Conclusion There are abundant variations in the AUF2 gene, which has a significant impact on the agronomic traits of flowering Chinese cabbage. These elite alleles and excellent haplotypes of AUF2 gene will benefit the genetic improvement of flowering Chinese cabbage.