Genome-Wide Characterization, Evolutionary Analysis of ARF Gene Family, and the Role of SaARF4 in Cd Accumulation of Sedum alfredii Hance

Auxin response factors (ARFs) play important roles in plant development and environmental adaption. However, the function of ARFs in cadmium (Cd) accumulation are still unknown. Here, 23 SaARFs were detected in the genome of hyperaccumulating ecotype of Sedum alfredii Hance (HE), and they were not evenly distributed on the chromosomes. Their protein domains remained highly conservative. SaARFs in the phylogenetic tree can be divided into three groups. Genes in the group Ⅰ contained three introns at most. However, over ten introns were found in other two groups. Collinearity relationships were exhibited among ten SaARFs. The reasons for generating SaARFs may be segmental duplication and rearrangements. Collinearity analysis among different species revealed that more collinear genes of SaARFs can be found in the species with close relationships of HE. A total of eight elements in SaARFs promoters were related with abiotic stress. The qRT-PCR results indicated that four SaARFs can respond to Cd stress. Moreover, that there may be functional redundancy among six SaARFs. The adaptive selection and functional divergence analysis indicated that SaARF4 may undergo positive selection pressure and an adaptive-evolution process. Overexpressing SaARF4 effectively declined Cd accumulation. Eleven single nucleotide polymorphism (SNP) sites relevant to Cd accumulation can be detected in SaARF4. Among them, only one SNP site can alter the sequence of the SaARF4 protein, but the SaARF4 mutant of this site did not cause a significant difference in cadmium content, compared with wild-type plants. SaARFs may be involved in Cd-stress responses, and SaARF4 may be applied for decreasing Cd accumulation of plants.