Genome-wide identification, characterization, evolutionary analysis, and expression profiling of the FCS-like zinc finger (FLZ) gene family in soybean (Glycine max L.) under abiotic stresses.

Drought and salinity limit soybean yield. Despite their role in the SnRK1 energy-sensing complex, a systematic study of FCS-Like Zinc Finger (FLZ) proteins in soybean has not been reported. We performed a genome-wide identification of the GmFLZ gene family, identifying 40 members distributed across 18 of the 20 soybean chromosomes. Phylogenetic analysis of 87 FLZ proteins from Glycine max, Arabidopsis thaliana, and Oryza sativa revealed four major evolutionary clades, suggesting that diversification predates the separation of monocots and dicots. Structural analysis identified ten conserved motifs, with Motifs 1 and 2 present in all family members. Gene duplication analysis identified 304 paralogous pairs, most arising from segmental duplication. Ka/Ks analysis indicated localized positive selection in six gene pairs and purifying selection in 97.9% of pairs. Tissue-specific expression profiling across nine tissues showed that GmFLZ5, GmFLZ15, GmFLZ25, and GmFLZ34 had the highest expression levels detected across the GmFLZ family, with GmFLZ5 the most highly expressed member in leaves, nodules, and stem and showing moderate expression in pod, root, and root hairs, whereas GmFLZ18, GmFLZ23, and GmFLZ37 showed root-preferential expression. RT-qPCR validation under drought (20% PEG-6000) and salt (200 mM NaCl) treatments in the Giza 5 cultivar showed that 36 and 34 of the 40 GmFLZ genes, respectively, exhibited at least a two-fold change in expression, with GmFLZ21 and GmFLZ35 among the most strongly induced under salt stress. These findings provide an evolutionary and functional framework for the GmFLZ family and identify candidate genes for future functional studies in soybean stress tolerance.