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

摘要

Sorghum Ma₆, a strong repressor of flowering in long days (LDs), was identified as the CONSTANS, CO-like, and TOC1 (CCT)-domain protein encoded by SbGhd7. Sorghum Ghd7 increases photoperiod sensitivity and delays flowering by inhibiting expression of the floral activator SbEhd1 and genes encoding FT. SbGhd7 expression is light-dependent and gated by the circadian clock. In LDs when flowering is repressed, SbGhd7 mRNA abundance peaks in the morning and evening. In short days (SDs) when floral initiation occurs, the evening phase of SbGhd7 expression occurs in darkness, reducing SbGhd7 mRNA abundance. In energy sorghum hybrids, dominant alleles of SbGhd7 and SbPRR37 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 SbGhd7 and SbPRR37 flower in 60 to 80 d. Recessive alleles of SbGhd7 and SbPRR37 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 ghd7-1 and prr37-1 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 SbGhd7 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.