A sorghum gigantea mutant attenuates florigen gene expression and delays flowering time

Authors: ABDUL-AWAL, S.M. - University Of California; Chen, Junping; Xin, Zhanguo; Harmon, Frank

Submitted to: Plant Direct
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2020
Publication Date: 11/13/2020
Citation: Abdul-Awal, S., Chen, J., Xin, Z., Harmon, F.G. 2020. A sorghum gigantea mutant attenuates florigen gene expression and delays flowering time. Plant Direct. 4(11). Article e00281. https://doi.org/10.1002/pld3.281.
DOI: https://doi.org/10.1002/pld3.281

Interpretive Summary: Flowering is an important physiological change for annual crop plants that represents an irreversible shift in development. Food production absolutely depends on flowering, while flowering is undesirable for promotion of biomass accumulation in forage and biofuel crops. The annual C4 grass sorghum is an important grain and subsistence crop, animal forage, and cellulosic biofuel feedstock that is tolerant of abiotic stresses and marginal soils. This work characterized a mutant in the sorghum GIGANTEA (SbGI) gene to identity flowering time genes and their regulatory relationships. This project discovered SbGI is an important upstream activator of other major floral regulators that themselves control florigen genes needed to trigger flowering. This study also discovered SbGI forms protein complexes with a flowering-associated of blue light photoreceptor. The hypothesis is SbGI protein regulates photoreceptor activity through this interaction. This work adds to the growing knowledge of flowering time pathways within of cereals and other grass crop species. From a practical standpoint, manipulation of how flowering genes like SbGI are expressed can be used for sorghum improvement as a grain crop, forage, or biofuel feedstock, as well as to ensure temperature sensitive phases of flowering and/or seed production occur before or after predictable stresses like periods of hot or cold weather. Finally, successful characterization of this gi mutant allele demonstrates the utility of sorghum mutant lines generated by USDA-ARS.

Technical Abstract: GIGANTEA (GI) is a conserved plant-specific gene that modulates a range of environmental responses in multiple plant species, including playing a key role in photoperiodic regulation of flowering time. The C4 grass Sorghum bicolor is an important grain and subsistence crop, animal forage, and cellulosic biofuel feedstock that is tolerant of abiotic stresses and marginal soils. To understand sorghum flowering time regulatory networks, we characterized the sbgi-ems1 nonsense mutation in the sorghum GIGANTEA (SbGI) gene from a sequenced M4 EMS-mutagenized BTx623 population. sbgi-ems1 plants flowered later than wild type siblings under both long-day or short-day photoperiods. Delayed flowering in sbgi-ems1 plants accompanied an increase in node number, indicating an extended vegetative growth phase prior to flowering. sbgi-ems1 plants had reduced expression of floral activator genes SbCO and SbEHD1 and downstream FT-like florigen genes SbFT, SbCN8, and SbCN12. Therefore, SbGI plays a role in regulating SbCO and SbEHD1 expression that serves to accelerate flowering. SbGI protein physically interacts with the sorghum FLAVIN-BINDING, KELCH REPEAT, F-BOX1-like (SbFFL) protein, a conserved flowering-associated blue light photoreceptor, and the SbGI-SbFFL interaction is stimulated by blue light. This work demonstrates SbGI is an activator of sorghum flowering time upstream of florigen genes under short- and long-day photoperiods, likely in association with the activity of the blue light photoreceptor SbFFL.