Ghd7 (Ma6) Represses Sorghum Flowering in Long Days: Ghd7 Alleles Enhance Biomass Accumulation and Grain Production

Abstract

Sorghum , a strong repressor of flowering in long days (LDs), was identified as the CONSTANS, CO-like, and TOC1 (CCT)-domain protein encoded by Sb. Sorghum Ghd7 increases photoperiod sensitivity and delays flowering by inhibiting expression of the floral activator Sb and genes encoding FT. Sb expression is light-dependent and gated by the circadian clock. In LDs when flowering is repressed, Sb mRNA abundance peaks in the morning and evening. In short days (SDs) when floral initiation occurs, the evening phase of Sb expression occurs in darkness, reducing Sb mRNA abundance. In energy sorghum hybrids, dominant alleles of Sb and Sb act in additive fashion to delay floral initiation for ∼175 d until daylengths decrease below 12.3 h. In contrast, photoperiod-insensitive grain sorghum genotypes containing recessive alleles of Sb and Sb flower in 60 to 80 d. Recessive alleles of Sb and Sb are present in historically important sorghum germplasm introduced into the United States in the 1800s that was used to produce early flowering grain and sweet sorghum. Recessive alleles and are present in maturity standards such as SM100, and in BTx406, a genotype used in the Sorghum Conversion Program to convert late-flowering photoperiod-sensitive sorghum accessions into early flowering photoperiod-insensitive germplasm useful for grain sorghum breeding. The results show that alleles of Sb confer differences in photoperiod sensitivity and flowering times that are critical for production of late-flowering high-biomass energy sorghum and early flowering grain sorghum.