Artificial selection for determinate growth habit in soybean

Area of Science:

• Plant genetics and molecular biology
• Crop domestication and evolution
• Agronomy and agricultural science

Background:

• Determinacy is a key agronomic trait in soybean (Glycine max) domestication, distinguishing cultivars into indeterminate and determinate growth habits.
• The wild progenitor, Glycine soja, exhibits an indeterminate growth habit, while soybean cultivars show segregation in a monogenic pattern between determinate (dt1/dt1) and indeterminate (Dt1/Dt1) genotypes.
• Understanding the genetic basis of determinacy is crucial for crop improvement and understanding domestication processes.

Purpose of the Study:

• To identify the gene responsible for soybean determinacy and its evolutionary relationship with homologous genes in other species.
• To investigate the role of human selection in the diversification of soybean growth habits.
• To elucidate the functional conservation and divergence between soybean and Arabidopsis floral meristem genes.

Main Methods:

• Positional cloning and gene identification to pinpoint the Dt1 locus.
• Comparative genomics to identify homologs in Arabidopsis thaliana.
• Functional analysis using transgenic Arabidopsis mutants to assess gene complementation.
• Genetic diversity assessment using simple sequence repeat (SSR) markers and allelic variation analysis in soybean landraces.

Main Results:

• The soybean Dt1 gene was identified as GmTfl1, a homolog of Arabidopsis terminal flower 1 (TFL1).
• Four distinct single-nucleotide substitutions in GmTfl1, each causing an amino acid change, are associated with the transition from indeterminate to determinate phenotypes in soybean.
• Genetic analysis suggests that human selection for determinacy occurred early in the radiation of Chinese soybean landraces.
• GmTfl1 functionally complements the determinate phenotype in Arabidopsis tfl1 mutants, indicating conserved function, while its homeolog shows signs of sub- or neo-functionalization.

Conclusions:

• GmTfl1 is the primary gene controlling soybean determinacy, evolving from an ancestral TFL1-like gene.
• Human selection played a significant role in shaping soybean growth habits through targeted mutations in GmTfl1 during early domestication.
• Differential functionalization of GmTfl1 and its homeolog contributes to the genetic diversity of soybean growth habits.