Soybean Protein Quality and Quantity: Genetic Control and Environmental Influences

Soybean [Glycine max (L.) Merr.] is a crucial global crop, serving as a primary source of high-quality plant protein. Its nutritional value is underscored by a nearly complete amino acid profile, though it is inherently deficient in sulphur-containing amino acids. As the demand for sustainable and health-promoting plant-based proteins surges, enhancing soybean seed protein content and quality has become a major breeding objective. However, this goal is challenged by a well-documented negative correlation between protein and oil content, as well as the significant influence of environmental factors on seed composition. This review synthesises recent advances in deciphering the genetic, molecular and physiological mechanisms governing protein accumulation. We explore the roles of key biosynthetic pathways, transcription factors and transporter genes, and discuss how their interplay with environmental cues-such as photoperiod, temperature, water availability and nutrient supply-shapes the final protein profile. A special emphasis is placed on the unique potential and challenges of cultivating high-protein soybeans in a low-latitude, distinct agro-climatic zone. By integrating genetic insights with an understanding of genotype-by-environment interactions, this work aims to provide a comprehensive theoretical framework for breeding next-generation soybean varieties with superior protein quality and stable yield under dynamic climatic conditions.