Identification of the soybean small auxin upregulated RNA ( SAUR ) gene family and specific haplotype for drought tolerance

Plants possess inherent mechanisms of dynamic responses to escape and/or adapt to adverse environmental stress. Small auxin upregulated RNA ( SAUR ) genes are a group of early auxin-responsive genes that play a crucial role in higher plant normal growth and environmental stimuli. The systematic analysis of the SAUR gene family and its corresponding impact under environmental pressure is worthy of careful discussion. In this study, the physicochemical properties, gene structure, phylogenetic analysis, cis -acting element, and selection pressure of Glycine max SAURs were analyzed using bioinformatics, expression profiles, and quantitative real-time PCR applied to assay the expression pattern of GmSAUR . In particular, haplotype analysis was used to obtain the candidate superior alleles of drought tolerance lost during domestication of wild soybean. A total of 253 GmSAUR genes were identified. These genes were not randomly distributed across the soybean chromosomes, as many of them were arranged in clusters on chromosomes 6, 9, and 12. Tandem duplication events and segmental duplication events may contribute to the expansion of the GmSAUR gene family. The phylogenetic analysis exhibited the 516 SAUR proteins from G. max , Arabidopsis thaliana , Populus trichocarpa , and Zea mays that could be divided into 13 groups, 11 of which contained GmSAUR members, in which 2 distinct groups formed soybean-specific clades. Gene structural analysis showed that 217 GmSAURs lack introns. Expression profiles based on RNA-Seq data revealed possible functional divergence among members of the GmSAURs . Six GmSAURs were found to be induced under dehydration stress based on RNA-Seq and qRT-PCR analyses. The π ratio (π G.max /π G.soja ) of GmSAUR genes from 302 soybean accessions showed that 13 members had strong selection signals during domestication. Interestingly, one haplotype in the GmSAUR299 promoter was identified that may be associated with soybean drought tolerance. This paper provides a new insight into future evolutionary and functional study of the soybean SAUR gene family and the genetic improvement of soybean.