Genome-Wide Characterization and Salt-Responsive Expression Divergence of Chromosome Group 2 and Group 6 TaBADH Genes in Wheat

Betaine aldehyde dehydrogenase (BADH) catalyzes the final step in glycine betaine biosynthesis, but the evolutionary divergence and differential salt responsiveness of BADH homeologs in bread wheat remain unclear. We identified six TaBADH genes and analyzed their phylogenetic relationships, conserved motifs, gene structures, promoter cis-acting elements and synteny. RNA-seq and qRT-PCR were used to compare expression in salt-tolerant Jimai 60 and salt-sensitive Chinese Spring under 200 mM NaCl, and BADH activity, glycine betaine, H2O2 and malondialdehyde (MDA) were measured during treatment. The genes separated into chromosome group 2 and group 6 clades with distinct structural and transcriptional patterns. TaBADH-2B encoded a shorter protein and lacked several conserved motifs. Group 6 genes showed stronger salt-responsive expression in Jimai 60, with TaBADH-6D displaying the strongest and most sustained induction. Jimai 60 also showed higher BADH activity and glycine betaine accumulation and lower H2O2 and MDA contents at later time points. Expression of TaBADH-6D improved E. coli growth under 200 mM NaCl. These findings identify homeolog-specific divergence within the BADH wheat family and support TaBADH-6D as a candidate for plant-level functional validation.