Genome-wide identification of the Glycine max (soybean) aspartate kinase (AK) gene family and functional analysis of the GmAK6 gene in seed amino acid metabolism.

INTRODUCTION: Aspartate kinase (AK) functions as a key regulatory enzyme in seed development and amino acid metabolism in plants. Although soybean (Glycine max) is a model high protein crop rich in essential amino acids, systematic characterization of its AK gene family remains limited. METHODS: To identify AK family genes at the genome wide level and analyze their functions, we performed a comprehensive bioinformatic analysis of the soybean genome, including phylogenetic reconstruction, promoter cis element prediction, transcriptomic profiling, and subcellular localization via GFP fusion assays. Functional validation was conducted using GmAK6 overexpressing transgenic soybean lines, with amino acid profiles quantified by HPLC. RESULTS: A total of 16 GmAK genes were identified, unevenly distributed across 10 chromosomes, with segmental duplication as the primary evolutionary driver of family expansion. Promoter analysis revealed that nearly half of the cis acting elements are associated with phytohormone signaling (e.g., jasmonic acid, abscisic acid) and abiotic stress responses (e.g., wounding, low temperature). Transcriptomic data showed distinct spatiotemporal expression patterns, with GmAK5 and GmAK6 significantly upregulated during seed development. GmAK6 was localized to chloroplasts. Amino acid profiling of GmAK6 overexpressing seeds demonstrated increased accumulation of methionine, threonine, and cysteine, alongside reduced levels of glutamate and proline. DISCUSSION: These results suggest that GmAK6 plays a regulatory role in amino acid metabolism during seed development and highlight the functional importance of AK genes in soybean.