Functional Study of a DREB homologous gene SsDREB from Suaeda salsa L. Screening of Promoter-Binding Factors of Tobacco PMT Gene Using a Modified Yeast Surface Display System Cloning and Function Analysis of ThDREB2B Gene Encoding a Putative DRE-binding Transcription Factor from Thellungiella halophila ThERF1 regulates its target genes via binding to a novel cis-acting element in response to salt stress