Genome-Wide Identification, Evolutionary Characterization, and Salt-Stress Expression Profiling of Antimicrobial Peptide Gene Families in the Xerophytic Recretohalophyte Reaumuria soongarica

Background/Objectives: Antimicrobial peptides (AMPs) contribute to plant innate immunity and abiotic-stress adaptation, but their repertoires remain poorly characterized in extremophytic plants. We aimed to define AMP gene families and their expression under Na2SO4 treatment in the xerophytic recretohalophyte Reaumuria soongarica. Methods: Six canonical AMP families were screened using hidden Markov model and homology searches, domain verification, gene-model and transcript-support assessment, nsLTP boundary curation, phylogenetic and synteny analyses, and reanalysis of public RNA-sequencing data from 0, 200, and 400 mM Na2SO4 treatments. Results: We identified 73 candidates: 15 defensins, 18 Snakin/GASA genes and 40 nsLTPs, including seven previously unannotated, transcript-supported models. RsLTP20 was reported separately as a reference-dependent C4-like candidate. Four sequence and alignment strategies supported two defensin, one Snakin/GASA and three nsLTP local groups. No tested promoter pattern was significantly enriched after multiple-testing correction. At 400 mM Na2SO4 relative to the control, 18 of the 66 catalogue members represented in the quantification reference were differentially expressed (12 upregulated and six downregulated; BH-adjusted p < 0.05 and |log2 fold change| > 1). Comparison with 38 Tamarix austromongolica candidates identified 27 reciprocal-best-hit pairs; genomic collinearity supported 25 direct candidate pairs. A separate Arabidopsis comparison recovered 26 candidate-anchored pairs. Conclusions: This curated catalogue defines conservative phylogenetic groups and provides candidates for experimental analysis of stress adaptation and peptide function.