Functional Study Of Auxin-responsive Genes TaSAUR78 And TaSAUR75 From Wheat (Triticum Aestivum L.) In Abiotic Stresses

High salt,drought and freezing are the major environmental factors that influence the growth of plant and account for significant reduction in the yields of crops.Wheat is one of the most widely cultivated and consumed food crops in the world.However wheat is sensitive to abiotic stress such as salt,drought.Therefore,it is essential to explore the key stress-tolerant genes and understand the molecular mechanism of abiotic stress tolerance in wheat.SAURs are the biggest family of early auxin response genes,which are small and sensitive to external stimulus.Former studies show that SAURs distribute widely in plants and regulate plant development and growth.It is reported that SAURs respond to abiotic stresses,but there are few reports about roles of SAURs in plant tolerance to abiotic stress.In this research,the functional study of auxin-responsive genes TaSAUR78 and TaSAUR75 in abiotic stresses was carried out to provide the candidate genes for crop breeding for abiotic stress tolerance.The main results were listed as follows:1.It was found that there were 274 TaSAURs in wheat through whole genome analysis.2.In this study,we cloned a novel SAUR gene,TaSAUR78,from wheat.By Y2H and BiFC validation,we found that TaSAUR78 interacts with TaVDAC1.Salinity stress decreases expression of TaSAUR78 and increases expression of TaVDAC1.Subcellular localization analysis showed that TaSAUR78 and TaVDAC1 may both function in the cytoplasm and nucleus.Overexpression of TaSAUR78 enhances tolerance to salt,drought and freezing stresses and up-regulates the expression of the stress relavant genes in transgenic Arabidopsis.Overexpressing TaSAUR78 reduces the accumulation of H₂O₂ in transgenic Arabidopsis under salt stress.Overexpression of TaVDAC1enhances tolerance to salt stress,while decreasing tolerance to drought and freezing stress in transgenic Arabidopsis.Expressions of stress relavant genes in TaSAUR78 are different from stress relavant genes in TaVDAC1 overexpression lines.TaSAUR78 overexpression decreases accumulation of H₂O₂ in plants after stress treatment,while TaVDAC1 overexpression increases the accumulation of H₂O₂ in plants after stress treatment.These results suggest that TaSAUR78 improves plant tolerance to abiotic stress by regulating TaVDAC1.This study generated valuable information on the functions of TaSAUR78 and TaVDAC1 in multiple abiotic stresses,which may facilitate the deployment of these genes to enhance crop tolerance to abiotic stresses in the future.3.We also identified another novel SAUR gene,TaSAUR75,in wheat.Expression of TaSAUR75was decreased in the roots of four varieties of wheat under salinity stress.A subcellular localization analysis suggested that TaSAUR75 may activate its targets in both the cytoplasm and nucleus of wheat protoplasts.Overexpression of TaSAUR75 in Arabidopsis enhanced drought and salinity tolerance.Furthermore,overexpression of TaSAUR75 enhanced plant cell tolerance to drought and salinity stress and maintained a higher chlorophyll content in leaves compared to that of wild-type plants after NaCl treatment.In addition,transcript levels of abiotic stress relavant genes were higher in TaSAUR75 plants than in the wild-type controls under drought and salinity stresses.These results suggested that the TaSAUR75 gene may function to positively modulate salinity and drought tolerance and have potential applications in molecular breeding of abiotic stress tolerance in crops.