HD1

HD1, or Heading Date 1, is a gene in rice (Oryza sativa) that plays a central role in controlling flowering time in response to day length. It encodes a transcription factor related to the CONSTANS family and contains domains that enable light- and circadian-regulated gene expression.

Functioning within the plant’s photoperiodic network, HD1 regulates the expression of Hd3a, a rice ortholog of FLOWERING LOCUS T. The effect of HD1 on flowering is day-length dependent: under short-day conditions it tends to promote Hd3a expression and flowering, while under long-day conditions it can contribute to repression of Hd3a, especially in conjunction with other regulators such as Ghd7. This dual activity helps rice adapt its flowering time to different latitudes and growing seasons.

Genetic and breeding significance arises from natural and induced variation at the HD1 locus. Different HD1 alleles can alter photoperiod sensitivity, enabling the development of cultivars that flower earlier or with reduced day-length dependence. Such variation is valuable for expanding the geographic range of rice cultivation and optimizing planting schedules.

Discovery and context place HD1 within a broader flowering-time network that includes other genes such as Hd3a, Ghd7, and Ehd1. HD1 is the rice homolog of Arabidopsis CONSTANS and is studied to understand how photoperiod signals are integrated to regulate flowering.

Note: HD1 can refer to other concepts in different fields; this article focuses on the HD1 gene in rice.