Comprehensive Analysis Of The Stress Associated Protein(SAP) Gene Family In Tamarix Hispida And The Function Of ThSAP6 In Salt Tolerance

Stress associated protein(SAP)is a type zinc finger protein-containing A20/AN1 domains that participates in various biotic and abiotic stress responses in plants.SAP participates in a series of physiological reactions by interacting with DNA or proteins as a transcription factor.However,little is known about the SAP gene family and their functions in Tamarix hispida.In this study,we isolated and characterized 11 SAPs from T.hispida.It is predicted that the number of amino acids encoded by these ThSAP genes is between 167-293,the estimated the molecular weight is about 18.24-32.23 kDa,and the theoretical isoelectric point(pI)is 6.86-9.14.The expression patterns of ThSAPs were analyzed under various stresses(salt and drought)and phytohormone treatment(SA,ABA and MeJA)using real-time quantitative reverse transcription polymerase chain reaction(RT-qPCR).Most ThSAPs exhibited transcriptional responses to abiotic stresses and phytohormones.Among these ThSAPs,ThSAP6 was significantly induced in all tissues by salt stress,indicating that it may play an important role in the response to salt stress of T.hispida.Therefore,we choose ThSAP6 for further research.ThSAP6 was fused to GFP under the control of CaMV 35S promoter,and was introduced into onion epidermal cells by particle bombardment.The results showed that ThSAP6 is a nuclear protein.The yeast two-hybrid system was used to identify the transcriptional activation activity and transcriptional activation domain of ThSAP6 protein,and it was determined that it has the activity of transcriptional activation and the transcriptional activation domain was conferred by the C-terminal,located at the 143-189 aa.It can be preliminarily determined that ThSAP6 protein functions as a transcription factor.Gain-and loss-of-function analyses revealed that ThSAP6 was a positive regulator of salt stress response.Overexpression of ThSAP6 in T.hispida increased antioxidant enzymes activity and proline content and decreased reactive oxygen species(ROS)accumulation and cell membrane damage under salt stress,while the opposite physiological changes were observed in ThSAP6-RNAi(RNA interference)lines.Arabidopsis thaliana was transformed by the plant overexpression vector and the transgenic lines of Arabidopsis were obtained.It found that the germination rate.root length,fresh weigh,growth status and physiological indicators of the transgenic lines were better than wild type plants.These indicated that ThSAP6 gene can significantly enhance the stress resistance of the plants by improving the ability to remove reactive oxygen species(ROS).