Preferential induction of <i>Dt2</i> gene in the absence of <i>E1</i> function enhances semi-determinate stem growth in soybean

Suitable plant architecture is key to maximizing crop yield. Stem growth habit is a crucial characteristic of soybean plant architecture. Here, we investigated the combined effect of the Dt2 gene (producing semi-determinate growth habit) and a loss-of-function e1-nl allele of the floral repressor E1. Comparisons among near-isogenic lines with different maturity genotypes indicated that the loss or repression of E1 function enhanced the effect of Dt2 on main stem node numbers. Dt2 expression in stem tips was upregulated in early growing stages under long-day conditions (LD) by the Dt2 and e1-nl alleles in an additive manner. Additionally, an Arabidopsis APETALA1 ortholog was highly upregulated in a Dt2/e1-nl line. The electrophoretic mobility shift assay revealed that the E1 DNA-binding domain bound to several genomic sites harboring key polymorphisms differentiating Dt2 from dt2 alleles. One of these sites had different transcription activities between Dt2 and dt2 alleles, and these activities were repressed by E1. Together, our data suggest that the Dt2 allele confers semi-determinacy by being preferentially induced when released from the repression by E1. The allelic combination of Dt2 and e1-nl confers a distinct semi-determinate phenotype, which would facilitate the use of the Dt2 allele, particularly under LD at high latitudes.