Functional characterization of SAUR genes in plant growth and development
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SAUR (small auxin up RNA) family of genes is one of the three early auxin responsive genes, expression of which is induced within minutes of auxin application. SAUR genes have been identified from several different model plants as well as economically important agricultural crops. The Arabidopsis genome contains more than 72 SAUR genes, spread across the five chromosomes and grouped into three clades. These genes code for relatively smaller proteins with a high degree of sequence similarity. Among more than 72 genes, functions of only a few of the genes have been identified. In the present study, four different SAUR genes from clade III were selected to examine their role in plant growth and development. Intracellular localization studies with GFP tagged proteins indicated that all the four SAUR proteins localized to the nucleus, cytoplasm, and the plasma membrane. Results indicate that these SAUR proteins positively regulate cell elongation probably by activating plasma membrane (PM) localized H+-ATPases. These SAUR genes were also found to be negative regulators of polar auxin transport and ethylene responses. Moreover, overexpression lines and loss-of-function mutants of SAURs display altered response to abiotic stress induced by salinity, abscisic acid and osmotic stress. Taken together, data presented here indicate that all four SAUR genes play an essential role in plant growth and development, as well as in plant responses to environmental stresses.