| Summary: | Brassinosteroid (BR) is an important steroid hormone that regulates plant development, abscisic acid (ABA) signaling, and responses to abiotic stress. We previously demonstrated that BEH3 (BES1/BZR1 Homolog 3) of <i>Arabidopsis</i> <i>thaliana</i> regulates dehydration and ABA responses by mediating proline metabolism. Furthermore, BEH3 negatively regulates BR-mediated hypocotyl elongation in dark-grown seedlings. However, the roles of <i>BEH3</i> ortholog genes in the osmotic stress response of plants have remained largely unknown. Here, <i>GmBEH3L1</i> (<i>Glycine max BEH3-Like 1</i>), a soybean (<i>G.</i> <i>max</i>) ortholog of the <i>BEH3</i> gene of <i>A. thaliana</i>, was isolated and functionally characterized. <i>GmBEH3L1</i> is induced by ABA, dehydration, and drought conditions. The <i>GmBEH3L1</i>-overexpressing transgenic lines (<i>GmBEH3L1</i>-OE/<i>beh3</i>) with the <i>beh3</i> mutant background have ABA- and dehydration-sensitive phenotypes during early seedling growth, implying that GmBEH3L1 is involved in both osmotic stress and ABA sensitivity as a negative regulator in <i>A. thaliana</i>. Consistent with these results, <i>GmBEH3L1</i>-OE/<i>beh3</i> complemental lines exhibit decreased expression levels of ABA- or dehydration-inducible genes. Under darkness, <i>GmBEH3L1</i>-OE/<i>beh3</i> complemental lines display a short hypocotyl length compared to the <i>beh3</i> mutant, indicating that GmBEH3L1 is linked to BR signaling. Together, our data suggest that GmBEH3L1 participates negatively in ABA and dehydration responses through BR signaling.
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