Szeluga, N. | Search bioRxiv

bioRxiv2025

Redesigning petal shape, size, and color in soybean reveals unexpected phenotypes for floral organ development

Soybean (Glycine max) has not yet benefited from large-scale hybrid breeding efforts due to its small, self-fertilizing flowers that are difficult to emasculate, and limited attractiveness to pollinators. This study explores targeted floral trait engineering to enhance pollinator attraction, aiming to overcome barriers to soybean hybridization. We generated a high-resolution floral organ expression atlas and H3K4 trimethylation ChIP-Seq dataset to identify candidate genes involved in petal development, nectar sugar content, and petal pigmentation. Using CRISPR-based activation and repression systems, we modified the expression of AINTEGUMENTA (GmANT), BIGPETAL (GmBPE), and SUCROSE TRANSPORTER2 (GmSUC2). Contrary to expectations based on Arabidopsis homologs, transcriptional activation of GmANT_B and repression of GmBPE led to reduced, rather than increased, petal size, highlighting divergent regulatory mechanisms in soybean. Complementation of the W1 gene that controls petal pigmentation successfully converted white petals to purple, with preliminary evidence indicating that this color conversion may increase pollinator visitation. These results underscore the complexity of floral development in soybean and provide foundational tools and resources for future efforts to engineer reproductive traits for hybrid seed production.

plant biology↗

bioRxiv2023

Introduction of Barnase/Barstar in soybean produces a rescuable male sterility system for hybrid breeding

Hybrid breeding for increased vigor has been used for over a century to boost agricultural outputs without requiring higher inputs. While this approach has led to some of the most substantial gains in crop productivity, breeding barriers have fundamentally limited soybean (Glycine max) from reaping the benefits of hybrid vigor. Soybean makes inconspicuous flowers that self-fertilize before opening, and thus are not readily amenable to outcrossing. In this study, we demonstrate that the Barnase/Barstar male sterility/male rescue system can be used in soybean to produce hybrid seeds. By expressing the cytotoxic ribonuclease, Barnase, under a tapetum-specific promoter in soybean anthers, we are able to completely block pollen maturation, creating male-sterile plants. We show that fertility can be rescued in the F1 generation of these Barnase-expressing lines when they are crossed with pollen from plants that express the Barnase inhibitor, Barstar. Importantly, we found that the successful rescue of male fertility is dependent on the relative dosage of Barnase and Barstar. When Barnase and Barstar were expressed under the same tapetum-specific promoter, the F1 offspring remained male-sterile. When we expressed Barstar under a relatively stronger promoter than Barnase, we were able to achieve a successful rescue of male fertility in the F1 generation. This work demonstrates the successful implementation of a biotechnology approach to produce fertile hybrid offspring in soybean.

plant biology↗