The plant hormone auxin plays a vital role in regulating many aspects of plant growth and development. Small auxin up-regulated RNAs (SAURs) are primary auxin response genes hypothesized to be involved in auxin signaling pathway, but their functions remain unclear. Here, a genome-wide search for SAUR gene homologues in Solanaceae species identified 99 and 134 members of SAUR gene family from tomato and potato, respectively. Phylogenetic analysis indicated that the SAUR proteins from Arabidopsis, rice, sorghum, tomato and potato were divided into four major groups with 16 subgroups. Among them, 25 histidine-rich SAURs genes with metal-binding characteristics were found in Arabidopsis, sorghum and Solanaceae species, but not in rice. Using tomato as a model, a comprehensive overview of SAUR gene family is presented, including the gene structures, phylogeny and chromosome locations. Quantitative real-time PCR analysis indicated that 11 randomly selected SlSAUR genes in tomato could be expressed at least in one of the tomato organs/tissues tested. However, different SlSAUR genes displayed distinctive expression levels. SlSAUR16 and SlSAUR71 exhibited highly tissue-specific expression patterns. Almost all of the detected SlSAURs showed an accumulating pattern of mRNA along tomato flower and fruit development. Some of them displayed differential response to exogenous IAA treatment. The abiotic (cold, salt and drought) stresses significantly modified transcript levels of SlSAURs genes. Most of them were down-regulated in response to abiotic stresses (drought, heat and salinity), but SlSAUR58, as a histidine-rich SAUR gene, was up-regulated after salt treatment, indicating that it may play a specific role in the salt signaling transduction pathway. Our comparative analysis provides some basic genomic information for the SAUR genes in the Solanaceae species and will pave the way for deciphering their function during plant development.
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