Molecular Basis of Soybean Stem Architecture

Soybean stem growth habit is an important morphological trait, which affect soybean yield potential and adaptability. Recently, we have identified two genes, Dt1, and Dt2, that control the stem growth habit in soybean, a critical agronomic trait that affects the plant’s yield potential and adaptability, and analyzed functional conservation and divergence between these genes and their duplicates. We found that the Dt1 is the functional counterpart of the Arabidopsis TFL1 – a floral suppressor gene primarily expressed in shoot apical meristems (SAMs) to prevent their switching from vegetative to reproductive state and thus produces indeterminate stems. The three Dt1 paralogs generated by the two rounds of WGDs in soybean were functionally diverged from Dt1 due to their sequence divergence in promoter regions, instead of protein-coding regions. In addition, our data revealed that Dt2 was a dominant MADS domain factor gene homologous to the Arabidopsis floral meristem (FM) identity gene AP1. However, unlike AP1, whose expression is limited to FMs in which the expression of TFL1 is repressed, Dt2 appears to be able to express in SAMs to repress the expression of Dt1 to promote early conversion of the SAMs into reproductive inflorescences, resulting in semi-determinate stems. We demonstrated that Dt2 was a recent gain-of-function mutation in its cis-regulatory region, which re-shaped the regulatory networks in semi-determinate soybean.