Sorghum bicolor INDETERMINATE1 is a conserved primary regulator of flowering

Authors: DE RISEIS, SAMUEL - University Of California Berkeley; Chen, Junping; Xin, Zhanguo; Harmon, Frank

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2023
Publication Date: 12/13/2023
Citation: De Riseis, S., Chen, J., Xin, Z., Harmon, F.G. 2023. Sorghum bicolor INDETERMINATE1 is a conserved primary regulator of flowering. Frontiers in Plant Science. 14. Article 1304822. https://doi.org/10.3389/fpls.2023.1304822.
DOI: https://doi.org/10.3389/fpls.2023.1304822

Interpretive Summary: The agricultural products of cereals largely depend on the production of seeds, which requires plants to form flowers. The timing of when plants begin to make flowering is tightly regulated and linked to both internal and external signals to the plant. Manipulation of genes that control flowering behavior in the cereal sorghum is a potential approach to adapt agriculture to different environments, but flowering genes and their interaction are incompletely understood in this plant. This work describes the identification and characterization of two previously unknown mutants that affect the same gene, known as INDETERMINATE1 (ID1). Changing ID1 function in corn or rice severely delays or blocks flowering, respectively. These sorghum ID1 mutants also cause later flowering, indicating a broad requirement for ID1 genes in the flowering of grasses used for agriculture. Overall, this study gives insight into the genes needed for grass plants to flower and, therefore, produce seeds.

Technical Abstract: A fundamental developmental switch for plants is transition from vegetative to floral growth, which integrates external and internal signals. Indeterminate (Id1) family proteins are zinc finger transcription factors that activate flowering in grasses regardless of photoperiod. Mutations in maize Id1 and rice Id1 (RID1) cause very late flowering. RID1 promotes expression of the flowering activator genes Early Heading Date1 (Ehd1) and Heading date 1 (Hd1), a rice homolog of CONSTANS (CO). Mapping of two recessive late flowering mutants from a pedigreed sorghum EMS mutant library identified two distinct mutations in the Sorghum bicolor Id1 (SbId1) homolog, mutant alleles named sbid1-1 and sbid1-2. The weaker sbid1-1 allele caused a 35 day delay is reaching boot stage in the field, but its effect was limited to 6 days under greenhouse conditions. The strong sbid1-2 allele delayed boot stage by more than 60 days in the field and under greenhouse conditions. When sbid1-1 and sbid1-2 were combined, the delayed flowering phenotype remained and resembled that of sbid1-2, confirming late flowering was due to loss of SbId1 function. Evaluation of major flowering time regulatory gene expression in sbid1-2 showed that Id1 is needed for expression of floral activators, like SbCO and SbCN8, and repressors, like SbPRR37 and SbGhd7. These results demonstrate a conserved role for SbID1 in promotion of flowering in sorghum, where it appears to be critical to allow expression of most major flowering regulatory genes.