Genome-wide identification and characterization of small auxin-up RNA (SAUR) gene family in plants: evolution and expression profiles during normal growth and stress response

Abstract

AbstractBackgroundAuxin is critical to plant growth and development, as well as stress responses.Small auxin-up RNA(SAUR) is the largest family of early auxin responsive genes in higher plants. However, the function of fewSAURgenes is known owing to functional redundancy among the many family members.ResultsIn this study, we conducted a phylogenetic analysis using protein sequences of 795 SAURs fromAnthoceros angustus,Marchantia polymorpha,Physcomitrella patens,Selaginella moellendorffii,Ginkgo biloba,Gnetum montanum,Amborella trichopoda,Arabidopsis thaliana,Oryza sativa,Zea mays,Glycine max,Medicago truncatulaandSetaria italica. The phylogenetic trees showed that the SAUR proteins could be divided into 10 clades and three subfamilies, and that SAUR proteins of three bryophyte species were only located in subfamily III, which suggested that they may be ancestral. From bryophyta to anthophyta,SAURfamily have appeared very large expansion. The number ofSAURgene in Fabaceae species was considerably higher than that in other plants, which may be associated with independent whole genome duplication event in the Fabaceae lineages. The phylogenetic trees also showed thatSAURgenes had expanded independently monocotyledons and dicotyledons in angiosperms. Conserved motif and protein structure prediction revealed that SAUR proteins were highly conserved among higher plants, and two leucine residues in motif I were observed in almost all SAUR proteins, which suggests the residues plays a critical role in the stability and function of SAUR proteins. Expression analysis ofSAURgenes using publicly available RNA-seq data from rice and soybean indicated functional similarity of members in the same clade, which was also further confirmed by qRT-PCR. Summarization of SAUR functions also showed that SAUR functions were usually consistent within a subclade.ConclusionsThis study provides insights into the evolution and function of theSAURgene family from bryophyta to anthophyta, particularly in Fabaceae plants. Future investigation to understand the functions ofSAURfamily members should employ a clade as the study unit.